Gsm Training

Fixed Network Planning In GSM Networks V-1.1

Course Information n

Course Title – Fixed Network Planning (GSM Version)

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Duration – 5 Days

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Target Audience – GSM Network Engineers

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Pre-requisite – Familiarity with – Basic Math and Probability, – Basic GSM Parameters and – RF Network Planning

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Instructor: Dr. Kamran Etemad

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Introduction Introduction & & Background Background Check Check n n n

Introduction Backgrounds Concerns& Interests

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Scope Scope of of the the Course Course

GSM Protocol Channelization, Network Elements (Review)

Call Flows and Signaling Protocols

Configuration & Planing

Traffic Theory

Network Dimensioning

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Outline Outline n

Chapter 1: – Introduction, GSM Protocol, Network Elements and RF Planning

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Chapter 2: – Call Flows and Signaling Network and Protocols

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Chapter 3: – Fundamentals of Traffic Models and Erlang Calculations

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Chapter 4: – Network Dimensioning

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Chapter 5: – Network Configuration & System Expansion

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Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

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Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

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Introduction: Introduction: GSM GSM History History n

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Global System for Mobile (GSM) is a second generation cellular system standard that was developed to solve the fragmentation problems of the first cellular systems in Europe. GSM is the world's first cellular system to specify digital modulation and network level architectures and services. Before GSM, European countries used different cellular standards throughout the continent, and it was not possible for a customer to use a single subscriber unit throughout Europe.

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GSM GSM in in the the World World n

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GSM was originally developed to serve as the panEuropean cellular service and promised a wide range of network services through the use of ISDN. GSM's success has exceeded the expectations of virtually everyone, and it is now the world's most popular standard for new cellular radio and personal communications equipment throughout the world. It is predicted that by the year 2000, there will be between 20 and 150 million GSM subscribers worldwide. Recently, GSM has changed its name to the Global System for Mobile Communications for marketing reasons. The setting of standards for GSM is currently under the aegis of the European Technical Standards Institute (ETSI). 8

Some Some of of GSM GSM System System Features Features n

Some of the important features of GSM: – Good subjective speech quality – Message Security – Maximum flexibility to provide services that are compatible with ISDN. – High data rate transfer, short bursts, slow frequency hopping, – Open-network architecture. – Use of the SIM (Subscriber Identity module) – Support international roaming. – Low terminal and Service Costs. 9

GSM GSM Services Services n

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Services are defined as anything the end user explicitly sees as worth paying for. Services are classified into three groups: – Tele-services, – Bearer Services – Supplementary Services.

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Tele -Services Tele-Services n

Speech Services – Telephony (+Voice Mail) – Emergency Calls

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Data Services – FAX group 3, alternate speech then fax – FAX group 3 automatic

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Short Message Service (SMS) – SMS is similar to the paging service, but much more comprehensive, allowing bi-directional messages, store-and-forward delivery, and acknowledgment of a successful delivery. 11

Additional Additional Data Data Services Services n

14.4 Circuit Switched – requires new channel coding – standardization – New Abis data framing

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High Speed Circuit Switched Data (HSCSD) General Packet Radio Service (GPRS)

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SMS SMS n

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Part of Tele-services described by GSM provides a mean for the Mobile Subscriber to send and receive short messages (<160 characters) via the Mobile unit. These services are – SMS point to point services » SMS Mobile Originating SMS-MO/PP » SMS Mobile Terminating SMS-MT/PP

888888

– SMS Cell Broadcast SMS-CB n

These services are provided by the Short Message Service Center (SM-SC). 13

Supplementary Supplementary services services n

These services are provided by the MSC/VLR but managed by the HLR – – – – – – –

Call Forwarding Unconditional (CFU) Call Forwarding Busy (CFB) Barring of Outgoing call Barring of incoming call Call Waiting Conference call Call Transfer

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Bearer Bearer Services Services n

PAD , Asynchronous access to PAD – 300 bps

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Packet Data, Synchronous access to PSPDN – 2.4,4.8 9.6 bps

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Alternate Speech/Data Unrestricted Digital Information (UDI) Asynchronous 300,1.2,2.4,4.8,9.6 bps Synchronous 1.2,2.4,4.8,9.6 bps

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GSM GSM Spectrum Spectrum Allocation Allocation Reverse Link Spectrum 880 MHz

50 frequencies

890 MHz

124 frequencies

Forward Link Spectrum 925 MHz

960 MHz

935 MHz 50 frequencies

915 MHz

124 frequencies

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Absolute Absolute Radio Radio Frequency Frequency Channel Channel

BTS TX

MS TX 200 kHz

200 kHz

45 MHz (890+n x 0.2)MHz

(935+n x 0.2) MHz

ARFCN = Absolute Radio Frequency Channel Number MS Transmit Frequency (MHz) = 890.0 + [(ARFCN)x(.2)] BTS Transmit Frequency (MHz) = 935.0 + [(ARFCN)x(.2)] 17

Physical Physical vs. vs. Logical Logical Channels Channels RF F5 Channels F4 F3 F2 F1 T0 T1 T2 T3 T4 T5 T6 T7 Time Slots n

n

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The combination of a TS number and an ARFCN constitutes a physical channel for both the forward and reverse link. Channelization is accomplished by the notion of virtual circuits or logical Channels. Each physical channel in a GSM system can be mapped into different logical channels at different times. 18

FDMA -TDMA FDMA-TDMA n n

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The frame duration is 4.645 ms divided among eight time slots. Each of these timeslots is a physical channel occupied by an individual user. Each timeslot, or physical channel, carries control and traffic data in a burst form. The time duration of an individual channel is 3/5200 sec(=0.577 ms).

RF Channels

200KHz

4.615msec Frame

Frequency

Time

T0 T1 T2 T3 T4 T5 T6 T7 T0 T1 T2 T3 T4 T5 T6 T7

Time Slot: 156.25bits 576.92µ µs

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Staggering Staggering TDMA TDMA Frames Frames n

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At the BTS, TDMA frames on all radio frequency channels, in the downlink as well as on the uplink, are aligned. However, the start of an uplink TDMA frame is delayed with respect to downlink by a fixed period of three timeslots. Staggering TDMA frames allows the same time slot number (TN) to he used in both the down and uplinks while avoiding the requirement for mobile to transmit and receive simultaneously. The TN within a frame is numbered from 0 to 7, and each TN can he referenced by a unique TN.

T0 T1 T2 T3 T4 T5 T6 T7

T0 T1 T2 T3 T4 T5 T6 T7 20

GSM GSM Burst Burst Types Types 1 TDMA frame =8 time slots (4.615 msec) n

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Each user transmits a burst of data during the time slot assigned to it.

0

1

2

3

4

5

6

7

Each TDMA time slot may carry one of five possible These data bursts may bursts. have one of five specific formats used for various – Normal Burst control and traffic – Frequency Correction Burst bursts. – Synchronization Burst – Random Access Burst – Dummy Burst 21

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

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n n n

Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

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Logical Logical Channels Channels n

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In a GSM system no RF carrier and no slot is dedicated a priori to an exclusive logical use. Channelization is accomplished by the data communications notion of virtual circuits or logical channels. According to the functions performed the channels are divided into two Logical Channels. – Traffic Channels (TCH) – Control Channels (CCH)

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GSM GSM Traffic Traffic Channels Channels n

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Full Rate – Full-Rate Speech Channel(TCH/FS) – Full-Rate Data Channel

Traffic Channels 2 half-rate channel users would share the same time slot, but would alternately transmit during every other frame.

There are two types of TCHs that are differentiated by their traffic rates and are defined as follows.

» 9.6kbps (TCH/F9.6) » 4.8kbps (TCH/F4.8) » 2.4kbps (TCH/F2.4) n

Half Rate – Half-Rate Speech Channel(TCH/HS) – Half-Rate Data Channel » 4.8kbps (TCH/H4.8) » 2.4kbps (TCH/H2.4)

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GSM GSM Control Control Channels Channels n

Broadcast CHannel (BCH) » Broadcast Control CHannel (BCCH) » Frequency Correction CHannel(FCCH) » Synchronization CHannel(SCH)

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Common Control CHannel (CCCH) » Paging CHannel(PCH) » Random Access CHannel(RACH) » Access Grant CHannel(AGCH)

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Dedicated Control CHannel (DCCH) » Stand-alone Dedicated Control Channel(SDCCH) » Slow Associated Control CHannel(SACCH) » Fast Associated Control CHannel(FACCH) 25

Broadcast Broadcast Control Control CHannel CHannel n

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The BCCH carrier broadcasts continuously for the MS to measure and average the signal strengths from a site, to identify the BTS with the best serving potential. At any base station, only one RF channel or carrier transmits the BCCH data: this RF channel is called the BCH carrier. The BTS will never reduce the power transmitting the BCH carrier because the MS’s need to measure the signal strengths from this frequency broadcasting at its maximum power or highest potential. The BTS must fill every timeslot on the BCCH carrier with a burst and if it has no “real” data to send to the MSs, the BTS will send a dummy burst.

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FCCH FCCH and and SCH SCH n

Frequency Correction Channel: – This logical channel is used for initial carrier acquisition or synchronization of the base station for the mobile unit

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Synchronization Channel: – The Frequency correction channel helps the mobile unit to get an estimate of the carrier frequency. For further tuning, and proper frame synchronization, the SCH is used.

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Common Common Control Control CHannel CHannel n

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CCCHs are the most commonly used control channels and are used to page specific subscribers, assign signaling channels to specific users, and receive mobile requests for service. Common Control Channel: The CCCH logical channel consists of: – Random Access Channel (RACH) in the Reverse direction. » The RACH is a reverse link channel used by MS to acknowledge a page from the PCH, and is also used by mobiles to originate a call.

– Paging Channel (PCH) or the Access Grant Channel (ACGH) in the Forward direction.

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Dedicated Dedicated Control Control CHannels CHannels n

Dedicated Control CHannel (DCCH) – Stand-alone Dedicated Control Channel(SDCCH) – Slow Associated Control CHannel(SACCH) – Fast Associated Control CHannel(FACCH)

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Like traffic channels – they are bi-directional and – have the same format and function on both the forward and reverse links. – may exist in any time slot and on any ARFCN except TS0 of the BCH ARFCN. 29

Stand Stand Alone Alone Dedicated Dedicated CCH CCH n

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SDCCH carries signaling data following the connection of the mobile with the base station, and just before a TCH assignment is issued by the base station. The SDCCH ensures that the mobile station and the base station remain connected while the base station and MSC verify the subscriber unit and allocate resources for the mobile. SDCCHs may be assigned their own physical channel or may occupy TS0 of the BCH if there is low demand for BCH or CCCH traffic. 30

Slow Slow Associated Associated CCH CCH n n

SACCH is always associated with a traffic channel or a SDCCH and maps onto the same physical channel. On the forward link, the SACCH is used to send slow but regularly changing control information to each mobile on that ARFCN, such as – power control instructions – specific timing advance instructions

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The reverse SACCH carries information about the received signal strength and quality of the TCH, as well as BCH measurement results from neighboring cells. 31

Fast Fast Associated Associated CCH CCH n

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FACCH carries urgent messages, and contains essentially the same type of information as the SDCCH. A FACCH is assigned whenever a SDCCH has not been dedicated for a particular user and there is an urgent message (such as a handoff request). The FACCH gains access to a time slot by stealing frames from the traffic channel to which it is assigned. This is done by setting two special bits, called stealing bits, in a TCH forward channel burst. If the stealing bits are set, the time slot is known to contain FACCH data, not a TCH, for that frame. Speech Frames FACCH Frames

Speech Frames 32

Signaling Signaling Outside Outside aa Call Call (TCH/8) (TCH/8) n

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In order to increase system efficiency when it comes to signaling transactions, an additional type of channel has been introduced. Its rate is very low and only has specified usage for signaling and short message transmission. This channel is referred as TCH/8. If a TCH/H is considered as half a TCH/F, then this is one-eighth of a TCH/F. A TCH/8 message is sent over one time slot for every other 8 frames.

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Cell Cell Broadcast Broadcast Channel Channel n

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Cell Broadcast Short message requires the means to transmit around one 80 octet message every two seconds from the network toward the mobile stations in idle mode. This corresponds to half the capacity of a downlink TCH/8. In each cell where this service is supported. a special channel a CBCH (Cell Broadcast Channel ) is used (or broadcasting messages. A CBCH is derived from a TCH/8. Some special constraints exist for the design of this channel. because of the requirement that it can be listened to in parallel with the BCCH information and the paging messages 34

Higher Higher Order Order Frame Frame n

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Higher order frames called multiframe, consist of 26 frames and have a duration of 120 ms (26 x 4.615 ms). This multiframe consists (of 26 TDMA) frames and carries a traffic channel TCH SACCH and FACCH. Similarly, a 51 -frame multi frame has a duration of 235.363 ms (51 x 4.615 ms). One superframe consists of 51 traffic multiframes or 26 control multiframes and consists of 51 x 26 TDMA frames with a total duration of 6.12 sec (51 x 120 ms). A 26 TDMA frame multiframe supports traffic and associated control channels, and a 51 TDMA frame multiframe supports Broadcast Control (BCC) and Stand Alone Dedicated Control Channels. The highest order frame is called a hyperframe and consists of 2,048 superframes, or 2,715,648 frames (2048 x 51 x 26). 35

Frame Frame Structure Structure Hierarchy Hierarchy 1 hyperframe = 2048 superframe = 2,715,648 frames (3hr, 28 min, 53 sec, 760 msec)

0

1

0 1

2

.........

2

50

2

25

1

2

3

1

2

25

1 superframe = 26 multiframes (6.12 sec)

0

1 26-frame multiframes (120 msec)

0

0

OR

1 superframe = 51 multiframes (6.12 sec)

0 1

2047

1

2

50

1 51-frame multiframes (235.4 msec)

4

5

6

7

1 TDMA frame = 8 time slots (4.615 msec)

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Structure Structure of of Control Control Multiframes Multiframes 235 ms = 51 FRAMES R R R R R R R R ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... R 0 1 2 3 4 5 6 7 8 9 ................................................................ 50 Uplink Direction --- All Frames/Slots Belong to the Rach

235 ms = 51 FRAMES F S B B B B C C C C F S C C C C C C C C F S C ... ... ..I 0 1 2 3 4 5 6 7 8 9 ................................................................ 50 Down Link Direction Frame/Slot Usage Is As Shown

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Inter -BTS Synchronization Inter-BTS Synchronization n

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Intercell-Synchronization impacts the quality of service in the area of handover performances. This notion of Synchronization includes also the desynchronization of the cells as we will see that full synchronization can be very detrimental to some aspects of system performance. Best performance is obtained when time bases in neighbor cells are synchronized so that burst emissions are synchronous, but de-synchronized so that in particular multiframes are not synchronous.

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Inter -BTS Synchronization Inter-BTS Synchronization n

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Synchronization between cells, if limited to bursts. can also be useful for pre-synchronization. It improves the search time for neighbor cells, though not in an obvious way. In fact all-clock phasing is the worst possible case for pre-synchronization performance. The best scheme for pre-synchronization is when cell clocks are organized to minimize the probability of simultaneity between FCCH. SCH or BCCH bursts in two adjacent cells.. This kind of "offset" synchronization is of course more complex to implement than an all-clock phasing synchronization. 39

GSM GSM Physical Physical Channels Channels Mobile Frequency (MHz) Total Spectrum (MHz) Number of Carriers Peak Power (mobile) Mean Power (mobile) n

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GSM DCS-1800 PCS-1900 Rx: 935-960 Rx: 1805-1880 Rx: 1930-1990 Tx: 890-915 Tx: 1710-1785 Tx: 1850-1910 2 x 25 2 x 75 2 x 60 124 372 300 8 ch./carrier 8 ch./carrier 8 ch./carrier .8-20 W .25-1 W .25-1 W .1-2.5 W .03-0.25 W .03-0.25 W

The most important difference between the DCS and GSM system is the frequency of operation and number of voice channels. DCS is restricted and optimized to two hand portable mobile power classes of the 1 Watt and .25 Watt peak power where as GSM mobile power is much higher..

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GSM GSM Physical Physical Layer Layer Parameters Parameters Multiple Access Method Duplex Method Carrier Spacing Modulation Modulation Rate Speech Codec Data Rate after Channel Coding Data Rate after Speech Coding Total Channel Bit Rate

GSM/DCS TDMA/FDM FDD 200 khz GMSK 271 kbps RPE-LTP 22.8 kbps 13 kps 270.833kbs

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Review of Functionalities Information Destination Source Source Decoder Decoder Secure, Reliable, Digital Memoryless Channel Insecure, Unreliable Digital Memoryless Channel Insecure, Unreliable Digital Fading Channel

Channel ChannelDecoder Decoder Decryption Decryption Deinterleaver Deinterleaver Demodulator Demodulator

Insecure Analog Fading Channel

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GSM GSM Speech Speech Coding Coding n

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The GSM speech coder is based on the Residually Excited Linear Predictive Coder (RELP) The coder provides 260 bits for each 20 ms blocks of speech, which yields a bit rate of 13 kbps. GSM voice coder uses – Voice Activity Detector (VAD) – Discontinuous Transmission (DTX) – Comforting Noise Subsystem (CNS)

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Provisions for incorporating half-rate coders are included in the specifications.

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CELP CELP based based Vocoders Vocoders

LPC filter Coef. Speech Analysis

M Pitch Parameters (Gain and Lag) U X Excitation Parameters (Index and Gain)

Channel Coder

Code Excited Linear Predictive (CELP) Coder Speech Synthesis

Excitation Pitch Try to imitate Vocal Cords

Vocal Tract Filter

Synthesized Speech

Tries to imitate Vocal Tract 44

Channel Channel Coding Coding

Speech Coder

Channel Encoder

Interleaver

CRC

Traffic Blocks

+

Convolutional Traffic Encoder

Frames Tail Bits

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Selective Selective Channel Channel Coding Coding n

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Not all 260 bits at the output of speech coder have the same importance as far as voice quality is concerned, In the order of their significance: Class 1a: 50 bits – protected with 3 CRC bits – If in error, entire block is ignored and interpolation is used

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Class 1b: 132 bits – (Class 1a+ CRC) + Class 1b + 4 tail bits are encoded, – using a convolutional encoder of rate 1/2 & constraint length 5 – The result is 378 bit

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Class 2: Remaining: 78 bits – are transmitted with no protection 46

Summary Summary of of Channel Channel Coding Coding 260 Voice bits/20msec Class 1a 50 bits

Class 1b 132 bits

Class 1a CRC 50 bits 3 bits

Class 1b 132 bits

Class 2 78 bits

4 Tail bits

No Coding

1/2 Rate Convolutional Encoder 378 Channel Encoded Bits

Class 2 78 bits

456bits Interleaving with degree 8 456=57*8 Channel bits/20msec=28.8kbps

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Diagonal Diagonal Block Block Interleaving Interleaving n

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Interleaving is used to randomize bursty errors due to fading effects. If a burst is lost due to interference or fading, channel coding ensures that enough bits will still be received correctly to allow the error correction to work. A1 A2 A3 A4 A5 A6 A7 A8

A1 B3

i

A2 B4

i+1

A3 B5

A4 B6

A5 B7

A6 B8

A7 B1

i+2

i+3

i+4

i+5

i+6

A8

i+7

Frame Number 48

Ciphering Ciphering n

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Ciphering modifies the contents of the eight interleaved blocks through the use of encryption techniques known only to the particular mobile station and base station. Security is further enhanced by the fact that the encryption algorithm is changed from call to call. Two types of ciphering algorithms, called A3 and A5, are used in GSM to prevent unauthorized network access and privacy for the radio transmission respectively. 49

Coding Coding for for Control Control Channels Channels n

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GSM control channel messages are defined to be 184 bits long. These bits are encoded using a shortened binary cyclic fire code, followed by a half-rate convolutional coder. The resulting 456 encoded bits are interleaved onto eight consecutive frames in the same manner as TCH speech data.

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Modulation Modulation n n n n

The modulation scheme used by GSM is 0.3 GMSK GMSK is a special type of digital FM modulation. The channel data rate of GSM is , 270.833 kbps, The MSK modulated signal is passed through a Gaussian filter to smooth the rapid frequency transitions which would otherwise spread energy into adjacent channels. 0100 1101.....

Mapping bit streams to waveforms 51

Slow Slow Frequency Frequency Hopping Hopping n

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Under normal conditions, each data burst is sent over the same time slot of a specific RF carrier. But – under sever fading conditions in a cell a low frequency hopping may be implemented to combat the multipath or interference effects. – Frequency hopping is carried out on a frame-by-frame basis. – Frequency hopping is completely specified by the service provider.

F1

F2 T=1

F3

F4 T=2

F5

F6

F7

F8

T=3 52

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

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Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM

n n n

Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

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System System Architecture Architecture n

A GSM system is basically designed as a combination of three major subsystems: – the Network Switching SubSystem (NSS) or (SSS) – the Radio Subsystem (RSS), or Base Station Subsystem (BSS) – the Operation Support Subsystem (OSS).

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The Mobile Station (MS) is usually considered to be part of the RSS.

Base Station Subsystem

Network Switching Subsystem Operation Support Subsystem

Public Networks

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Network Network Architecture Architecture Base Station BTS Subsystem

BTS MS

BSC

Network Switching Subsystem

EIR

IWF

ISDN

BTS

MSC

BTS BTS

MS

EC

Public Networks

BTS

BSC

HLR

VLR

OMC

PSTN AUC

Data Networks

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The The Radio Radio subsystem subsystem n

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The radio subsystem includes the equipment and functions related to the management of the connections on the radio path, including the management of handovers. It mainly consists of a BSC, BTS, and the MS. The GSM system is realized as a network of radio cells. Each cell has a BTS with several transceivers. A group of BTSs are controlled by one BSC. BSC and BTS together are known as a BSS, which is viewed by the MSC through a single interface as being the entity responsible for communication with MSs in a certain area. 56

Network Network Subsystem Subsystem n

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The network subsystem includes the equipment and functions related to end-to-end calls, management of subscribers, mobility, and interface with the fixed PSTN. The network and the switching subsystem together include the main switching functions of GSM as well as the databases needed for subscriber data and mobility management Network Switching Subsystem In particular, the switching subsystem consists of – – – – – – – –

Mobile Switch Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR), Authentication Center (AUC), and Equipment Identity Register (EIR) Echo Canceller (EC) InterWorking Function (IWF) ......

EIR

EC

IWF

MSC HLR

VLR

AUC

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Operation Operation Support Support Subsystem Subsystem n

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The Operational and Maintenance Center (OMC) subsystem includes the operation and maintenance of GSM equipment and supports the operator network interface. It is connected to all equipment in the switching system and to the BSC. OMC performs GSM's administrative functions (for example, billing) within a country. One of the OMC's most important functions is the maintenance of the country's HLR.

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GSM GSM Hierarchical Hierarchical Network Network Structure Structure n

In the GSM system, the network is divided into the following partitioned areas. – – – – –

GSM service area; PLMN service area; MSC service area; Location area (LA); Cells GSM Service Area PLMN

MSC Service Area

LA

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GSM GSM Service Service Area Area & & PLMN PLMN n

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The GSM service area is the total area served by the combination of all member-countries where a mobile can be serviced. The next level is the PLMN service area. There can be several within a country, based on its size. – The links between a GSM/ PLMN network and other PSTN, ISDN, or PLMN networks will be on the level of international or national transit exchanges. – All incoming calls for a GSM/PLMN network will be routed to a Gateway MSC. – Call connections between PLMNs, or to fixed networks, must be routed through certain designated MSCs called a gateway MSC. 60

MSC MSC Service Service Area Area & & Location Location Area Area n

In one PLMN there can be several MSC/VLR service areas. – MSC/VLR is a sole controller of calls within its jurisdiction. The mobile location can be uniquely identified since the MS is registered in a VLR, which is generally associated with an MSC. – There are several LAs within one MSC/VLR combination. – A LA is a part of the MSC/VLR service area in which a MS may move freely without updating location information to the MSC/VLR exchange that controls the LA.

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Lastly, a LA is divided into many cells. – A cell is an identity served by one BTS. The MS distinguishes between cells using the Base Station Identification Code (BSIC) that the cell site broadcasts over the air 61

MS MS Functions Functions n

A list of relevant MS functions includes – – – – – – –

Voice and data transmission; Frequency and time synchronization; Monitoring of power and signal quality of the surrounding cells for optimum handover; Provision of location updates; Equalization of multipath distortions; Display of short messages up to 160 characters long; Timing advance.

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MS MS Identification Identification n

GSM uses a number of descriptors to identify subscribers, equipment, and fixed stations/areas. Many are temporary and used to maintain the confidentiality of fixed identities. An understanding of these descriptors is essential when considering GSM exploitation. – – – –

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International Mobile station Equipment Identity (IMEI) Mobile Subscriber ISDN Number (MSISDN) International Mobile Subscriber Identity (IMSI) Temporary Mobile Subscriber Identity (TMSI)

In general, identities are used in the interfaces between the MSC and the MS, while numbers are used in the fixed part of the network, such as, for routing. 63

n

n

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By making a distinction between the subscriber identity and the mobile equipment identity, a GSM PLMN can route calls and perform billing based on the identity of the subscriber rather than the mobile unit being used. This can be done using a removable Subscriber Identity Module (SIM). The smart card SIM is portable between Mobile Equipment (ME) units.

SIM

SIM SIM Card Card

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SIM SIM (cont.) (cont.) n

The contents of the SIM card are as follows. – Removable plastic card or the SIM module; – Unique mobile subscriber ID through IMSI and ISDN numbers; – PIN; – Authentication key Ki and A3, AS, and A8 algorithms.

n

n

The SIM is a removable SC, the size of a credit card, and contains an integrated circuit chip with a microprocessor, random access memory (RAM), and read-only memory (ROM). A smart card (SC) is one possible implementation of a SIM; the other implementation can be the module mounted on the mobile equipment. 65

IMEI IMEI n

The IMEI is the unique identity of the equipment used by a subscriber by each PLMN and is used to determine – authorized (white), – unauthorized (black), and – malfunctioning (gray) GSM hardware.

n

n

In conjunction with the IMSI, it is used to ensure that only authorized users are granted access to the system. An IMEI is never sent in cipher mode by a MS 66

IMSI IMSI n n

International Mobile Subscriber Identity An IMSI is assigned to each authorized GSM user. It consists of a – a mobile country code (MCC), – a mobile network code (MNC), and – a PLMN unique mobile subscriber identification number (MSIN).

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The IMSI is not hardware-specific. Instead, it is maintained on a SC by an authorized subscriber and is the only absolute identity that a subscriber has within the GSM system. The IMSI shall not exceed 15 digits.

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TMSI TMSI n

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TMSI is a temporary identification number that is assigned by the serving MSC/VLR combination. It is assigned only after successful subscriber authentication. Since the TMSI has only local significance (that is, within the VLR and the area controlled by the VLR), the structure of this can be chosen by each administration in order to meet local needs. The TMSI is mainly used for security reasons to avoid broadcasting the IMSI over the RF air interface, thereby making it harder for eavesdroppers. The TMSI is supposed to be changed on a per-call basis as recommended by GSM specific actions. 68

MS -ISDN MS-ISDN n

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Mobile Station ISDN Number: The MS international number must be dialed after the international prefix in order to obtain a mobile subscriber in another country. The MSISDN number is composed of – the country code (CC) followed by – the National Significant Number (N(S)N), which shall not exceed 15 digits.

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The Mobile Station Roaming Number (MSRN): is allocated on a temporary basis when the MS roams into another numbering area. The MSRN number is used by the HLR for rerouting calls to the MS.

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Base Base Station Station System System n

n

The BSS is a set of BS equipment (such as transceivers and controllers) that is in view by the MSC through a single A interface as being the entity responsible for communicating with MSs in a certain area. The function split is basically between a transmission equipment, the BTS, and a managing equipment at the BSC. – A BTS comprises radio transmission and reception devices, up to and including the antennas, and also all the signal processing specific to the radio interface. – A BSC is a network component in the PLMN that functions for control of one or more BTS. It is a functional entity that handles common control functions within a BTS.

n

The interface between the BSC and a remote BTS is a standard interface termed the A-bis. BSC BTS

70

Base Base Transceiver Transceiver Subsystem Subsystem n

n

A BTS is a network component that serves one cell and is controlled by a BSC. BTS is typically able to handle three to five radio carriers, carrying between 24 and 40 simultaneous communications. Um

TRXn TRXn-1 TRX2 TRX1

BSC

Abis

BCF BTS

71

BTS BTS Functions Functions n

A list of functions performed by BTS is as follows. – BTS Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna; – Transcoding and rate adaptation; – Time and frequency synchronization signals transmitted from BTS; – Voice communication through full rate or half rate (future date) speech channel; – Received signal from mobile is decoded, decrypted and equalized before demodulation; – Frequency hopping controlled such that no two MSs in the same BSC area are hopped together; – Random access detection; – Timing advance; – Uplink radio channel measurements. BTS

72

Transcoder /Rate Adapter Transcoder/Rate Adapter Unit Unit n

n

The Transcoder/Rate Adapter Unit (TRAU) is the equipment in which coding and decoding is carried out as well as the rate adaptation in case of data. The transcoder takes 13-Kbps speech or 3.6/6/12-Kbps data and multiplexes four of them to convert into standard 64-Kbps data. – First, the 13 Kbps or the data at 3.6/6/12 Kbps are brought up to the level of 16 Kbps by inserting additional synchronizing data to make up the difference between a 13-Kbps speech or lower rate data, and then four of them are combined in the transcoder to provide 64 Kbps. – Then, up to 30 such 64-Kbps channels are multiplexed onto a 2.048 Mbps if a CEPT1 channel is provided on the A-bis interface.

4 x Coded Speech Channels

TRAU

64 Kbps 73

TRAU TRAU (cont.) (cont.) n

Depending on the relative costs of a transmission plant for a particular cellular operator, there may be some benefit, for larger cells and certain network topologies, in having the transcoders either at the BTS, BSC, or MSC location. – If the transcoder is located at MSC, they are still considered functionally a part of the BSS. This approach allows for the maximum of flexibility and innovation in optimizing the transmission between MSC and BTS. – If the transcoder/rate adapter is placed outside the BTS (part of BSC or MSC), the A-bis interface can only operate on a 16-Kbps channel within the BSS. Four traffic channels can then be multiplexed on one 64-Kbps circuit. Thus, the TRAU output data rate is 64 Kbps. 74

TRAU TRAU Location Location To MS

BTS

To MS

BTS

To MS

BTS

RF Air Interface

TRAU

BSC

A-bis Interface

BSC

MSC

To Fixed Networks

TRAU

MSC

To Fixed Networks

BSC

TRAU

To Fixed Networks

A Interface

13 kbps encoded voice / 12 kbps data

16 kbps transmission

MSC

64 kbps transmission Physical site 75

Base Base Station Station Controller Controller n

n

The BSC is connected to the MSC on one side and to the BTSs on the other. The BSC performs the Radio Resource (RR) management for the cells under its control.

BTS MSC BTS

BSC

76

BSC BSC Functions Functions n

The functions of BSC are as follows. RR management for BTSs under its control; Intercell handover; Reallocation of frequencies among BTSs; Power management of BTSs; Time and frequency synchronization signals to BTSs; Time delay measurement of the received signals from MSs with respect to BTS clock; – Controls frequency hopping; – Performs traffic concentration to reduce the number of lines from BSC to MSC and BTSs; – Provides interface to the Operations and Management for BSS. – – – – – –

77

BTS -BSC Connections BTS-BSC Connections TRX Abis

BTS1

BCF

B S C

Abis

Abis

Abis

TRX TRX TRX

TRX TRX TRX TRX

BCF BTS4

TRX TRX TRX BCF

BTS2

TRX TRX TRX BCF BTS378

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

n

n n n

Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

79

Mobile Mobile Switch Switch Center Center (MSC) (MSC) n

n

n

n

The main role of the MSC is to manage the communications between the GSM users and other telecommunications network users. The basic switching function is performed by the MSC, whose main function is to coordinate setting up calls to and from GSM users. The MSC has interfaces with the BSS on one side (through which MSC VLR is in contact with GSM users) and the external networks on the other (ISDN/PSTN/PSPDN) An MSC is generally connected to several BSSs, which provide radio coverage to the MSC area. MSC is also connected to other GSM PLMN entities such as other MSCs and HLR through a fixed network.

EIR

EC

IWF

MSC HLR

VLR

AUC

80

MSC MSC (cont.) (cont.) n

n

n

The MSC provides the interface between the fixed and mobile networks. The MSC is the telephone switching office for mobileoriginated or terminated traffic. The MSC controls the call setup and routing procedures in a manner similar to the functions of a land network end office. The MSC provides

EIR

EC

IWF

MSC HLR

VLR

AUC

– call setup, – routing, and – handover between BSCs in its own area and to/from other MSC; – an interface to the fixed PSTN; – and other functions such as billing. 81

MSC MSC Functions Functions n

Some of functions performed by MSC –

Paging;

–

Coordination of call set up from all MSs in its jurisdiction; Dynamic allocation of resources; Handover management; Reallocation of frequencies to BTSs in its area to meet heavy demands;

– – – n

n

Specifically, the call-handling function of paging is controlled by MSC. MSC coordinates the set up of calls to and from all GSM subscribers operating in its area. The dynamic allocation of access resources is done in coordination with the BSS. More specifically, the MSC decides when and which types of channels should be assigned to which MS. The channel identity and related radio parameters are the responsibility of the BSS. 82

MSC MSC Functions Functions (cont.) (cont.) n

Some of other functions performed by MSC – – – – – – –

Location registration; Billing for all subscribers based in its area; Encryption; Signaling exchange between different interfaces; Synchronization with BSSs; One MSC may interface several BSSs Some other network elements are:

83

Visitor Visitor Location Location Register Register n

n

n

The VLR Constitutes the database that supports the MSC in the storage and retrieval of the data of subscribers present in its area. The VLR supports a mobile paging and tracking subsystem in the local area where the mobile is presently roaming. A VLR may be in charge of one or several MSC LAs.

84

VLR VLR and and Location Location Updating Updating n

n

n

When a mobile subscriber roams from one LA to another, their current location is automatically updated in their VLR. If the old and new LAs are under the control of two different VLRs, the entry on the old VLR is deleted and an entry is created in the new VLR by copying the basic data from the HLR. The subscriber's current VLR address, stored at the HLR, is also updated. This provides the information necessary to complete calls to roaming mobiles. LAI LAI-2 1

MSC1

MSC2

6

VLR1

VLR2

3 4

Delete This MS From Database

2

HLR

5

Delete This MS to Database

85

Location Location Update Update n

n

n

n

n

MS must request a location update when an optional timer expires. This periodic updating increases the accuracy of the data in the VLR. The BTS broadcasts the timer on the BCCH to tell the MS how often to update locations within a LAI. The MS must go from the idle mode to the dedicated mode and back to the idle mode to complete a location update. SDCCH is the channel that the MS and BTS use for a location update. The MS does not update locations during a call. 86

Data Data in in VLR VLR n

Data stored in VLR are as follows. – – – – – – – – –

IMSI MSISDN MSRN TMSI The LA where the MS has been registered Supplementary service parameters MS category Authentication key, query and response obtained from AUC ID of the current MSC 87

VLR VLR Functions Functions n

VLR – – –

– –

Works with the HLR and AUC on authentication; Relays cipher key from HLR to BSS for encryption/decryption; Controls allocation of new TMSI numbers; a subscriber's TMSI number can be periodically changed to secure a subscriber's identity; Supports paging; Tracks state of all MSs in its area. 88

Home Home Location Location Register Register n

n

n

n

The HLR is the reference database that permanently stores data related to a given set of subscribers. Various identification numbers and addresses as well as authentication parameters, services subscribed, and special routing information are stored. Current subscriber status, including a subscriber's temporary roaming number and associated VLR if the mobile is roaming, are maintained. Location registration is performed by HLR.

89

HLR HLR Functions Functions n

n

n

n

n

n

The HLR provides data needed to route calls to all MS-SIMs home based in its MSC area, even when they are roaming out of area or in other GSM networks. The HLR provides the current location data needed to support searching for and paging the MS-SIM for incoming calls, wherever the MS-SIM may be. The HLR is responsible for storage and provision of SIM authentication and encryption parameters needed by the MSC where the MS-SIM is operating. It obtains these parameters from the AUC. The HLR maintains records of which supplementary services each user has subscribed to and provides permission control in granting access to these services. Both the HLR and the VLR can be implemented in the same equipment in an MSC (collocated). A PLMN may contain one or several HLRs.

90

HLR HLR Data Data n

Based on described functions, different types of data are stored in HLR. – Some data are permanent; that is, they are modified only for administrative reasons, – while others are temporary and modified automatically by other network entities depending on the movements and actions performed by the subscriber. – Some data are mandatory, other data are optional.

91

HLR HLR Data Data (Permanent) (Permanent) n

n

n n n n

n

IMSI: It identifies unambiguously the MS in the whole GSM system; International MS ISDN number: It is the directory number of the mobile station; MS category specifies whether a MS is a pay phone or not; Roaming restriction (allowed or not); Closed user group (CUG) membership data; Supplementary services related parameters: Forwarded-to number, registration status, no reply condition timer, call barring password, activation status, supplementary services check flag; Authentication key, which is used in the security procedure and especially to authenticate the declared identity of a MS. 92

HLR HLR Data Data (Temporary) (Temporary) n

The temporary data consists of the following. – – – – – – –

n

LMSI (Local MS identity); RAND/SRES and Kc; data related to authentication and ciphering; MSRN; VLR address, which identifies the VLR currently handling the MS; MSC address, which identifies the MSC area where the MS is registered; Roaming restriction; Messages waiting data (used for SMS);

Temporary data changes from call to call. The HLR interacts with MSCs mainly for the procedures of interrogation for routing calls to a MS and to transfer charging information after call termination.

93

Authentication Authentication Center Center

n

n

n

Authentication information and ciphering keys are stored in a database within the AUC, which protects the user information against unwanted disclosure and access. The HLR is also responsible for the "authentication" of the subscriber each time he makes or receives a call. The AUC, which actually performs this function, is a separate GSM entity that will often be physically included with the HLR. Being separate, it will use separate processing equipment for the AUC database functions. 94

Authentication Authentication Concept Concept

Number Shared Secret Data

Authentication Algorithm

No Matched ?

At Mobile Unit

AIR Interface

At Serving System Random

Authentication Algorithm

Shared Secret Data

Authentication Response

Yes Access Denied

Access Granted.

95

Authentication Authentication Process Process n n n

n

n n

n

A PIN number is used to activate the MS. MS sends its IMSI The network sends back a randomly generated number (RAND). MS computes the Signed Response (SRES) using an authentication algorithm (A3), the Key which is like a shared secret data, and RAND. MS send the SRES to the network The network computes SRES independently and compare is with the received SRES from mobile. A match indicates an authorized user whereas a mismatch results in failed authentication and no service. 96

Key Key Exchange Exchange n

n

n

n

n

In the authentication procedure, the key is never transmitted to the mobile over the air path, only a random number is sent. In order to gain access to the system, the mobile must provide the correct Signed Response (SRES) in answer to a random number (RAND) generated by AUC. Also, K1 and the cipher key Kc are never transmitted across the air interface between the BTS and the MS. Only the random challenge and the calculated response are transmitted. Thus, the value of Ki and Kc are kept secure. The cipher key, on the other hand, is transmitted on the SS7 link between the home HLR/AUC and the visited MSC, which is a point of potential vulnerability. On the other hand, the random number and cipher key is supposed to change with each phone call, so finding them on one call will not benefit using them on the next call. 97

Equipment Equipment Identity Identity Register Register n

n

n

EIR is a database that stores the IMEI numbers for all registered ME units. EIR database stores the ME identification and has nothing to do with the subscriber who is receiving or originating a call. There are three classes of ME that are stored in the database, and each group has different characteristics. – – –

White List: contains those IMEIs that are known to have been assigned to valid MSs. Black List: contains IMEIs of mobiles that have been reported stolen. Gray List: contains IMEIs of mobiles that have problems (for example, faulty software, wrong make of the equipment). This list contains all MEs with faults not important enough for barring. 98

Interworking Interworking Function Function (IWF) (IWF) n

n

n

A GSM system provides a wide range of data services to its subscribers and interfaces with the various forms of public and private data networks currently available. It is the job of the IWF to provide this interfacing capability. Networks to which IWF presently provides interface are as follows. – PSTN; – ISDN; – Circuit-switched public data networks (CSPDN); – Packet-switched public data networks (PSPDN). 99

Echo Echo Canceller Canceller (EC) (EC) n n

The EC is used on the PSTN side of the MSC for all voice circuits. The EC is required at the MSC PSTN interface to reduce the effect of GSM delay when the mobile is connected to the PSTN circuit.

PLMN 4 wire circuit

BSS

MSC

MS

EC

4w to PSTN 2w Hybrid bridge

Land telephone

100

Echo Echo Canceller Canceller (Cont.) (Cont.) n

n

n

Normally this delay would not be an annoying factor to the mobile, except when communicating to PSTN as it requires a two-wire to four-wire hybrid transformer in the circuit. Due to the presence of this hybrid, some of the energy at its four-wire receive side from the mobile is coupled to the four-wire transmit side and thus retransmitted to the mobile. This causes the echo The resulted echo does not affect the land subscriber but is an annoying factor to the mobile. The standard EC cancels about 70 ms of delay.

101

Some Some Other Other Network Network Elements Elements n

Gateway MSC is the anchor MSC which has direct signaling interaction with PSTN. – It is the gateway of the GSM network to/from outside network.

GMSC

MSC MSC

n

n

P S T N

Message Center (MC): or Voice Mail Services (VMS), which handles voice mail messaging and stores/forwards voice mails. Billing Center (BC): Keep track of charges for all mobile in the network. 102

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

n

n n n

Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

103

Operations Operations & & Maintenance Maintenance Center Center n

n

n

The main purpose of the OMC is to perform all operations and maintenance functions on elements of the GSM PLMN system. The OMC uses a separate Telecommunications Management Network (TMN) to communicate with the various components of the GSM system. In general, it is done through leased lines on the PSTN or other fixed networks. The OMC message and data transfers can either be carried by SS7 or X.25 protocols.

104

Intra -Network OMC Intra-Network OMC Connections Connections

Base Station Subsystem

BTS

Public Networks

Network Switching Subsystem

EIR

EC

ISDN

IWF

MSC

BSC

PSTN

MS HLR

AUC VLR

Data Networks

X.25

OMC 105

OMC OMC Functions Functions n

n

Maintenance functions cover both technical and administrative actions to maintain and correct the system operation, or to restore normal operations after a breakdown, in the shortest possible time. the following network functions are performed. – – – – – – – –

Supports for maintenance; X.25 interface; Alarm handling; Fault management; Performance management; Software version and configuration control; Network status; Traffic collection from network. 106

OMC OMC (cont.) (cont.) n n

n

n

n

A mobile call trace facility can also be invoked. The performance management functions include collecting traffic statistics from the GSM network entities and archiving them in disk files or displaying them for analysis. Because a potential to collect large amounts of data exists, maintenance personnel can select which of the detailed statistics to be collected based on personal interests and past experience. The OMC provides system change control for the software revisions and configuration data bases in the network entities. Software loads can be downloaded from the OMC to 107 other network entities or uploaded to the OMC.

Network Network Management Management Center Center n

The salient characteristics and features of the NMC are as follows. – Single NMC per network; – Provides traffic management for the whole network; – Monitors high-level alarms such as failed or overloaded nodes; – Performs responsibilities of an OMC when it is not staffed; – Provides network planners with essential data for network performance.

n

The NMC is generally connected to the PLMN subsystems through leased lines via PSTN. 108

OMC OMC vs. vs. MNC MNC n

n

n

OMC is a regionalized management center, OMC is used for monitoring and controlling the daily activities of the system operations, OMC is used by network operators

n

n

n

while NMC is the global management center. while NMC is for the long-term planning.

while NMC is used by network managers and network planners.

109

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

n

n n n

Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

110

GSM GSM Interfaces Interfaces GSM Um Radio Air Interface

Abis Interface

A Interface

SS7

BTS

MS

BSC

BTS

MSC

PSTN

BTS n

There are three dominant interfaces, namely, an interface between MSC and the Base Station Controller (BSC), an A-bis interface between BSC and the Base Transceiver Station (BTS), and an Urn interface between the BTS and MS.

111

Abis Abis Interface Interface n

n

n

All the data, both signaling and user data, move between the base station (the BTS part) and the BSC on the Abis interface. The Abis is implemented when the BTS and BSC are located at different sites. If both are positioned at the same location, even in the same cabinet or rack, different solutions are possible, depending on the manufacturer. Due to its late and initially fragmented standardization, the Abis interface appeared in a variety of different interpretations and implementations. This led to incompatibilities among network components from different manufacturers. So, if network operators decided to buy a BSC from one supplier, they had little choice but to buy BTSs from the same supplier 112

BTS -BSC Connections BTS-BSC Connections TRX Abis

BTS1

BCF

B S C

Abis

Abis

Abis

TRX TRX TRX

TRX TRX TRX TRX

BCF BTS4

TRX TRX TRX BCF

BTS2

TRX TRX TRX BCF BTS3113

Digital Transmission Links n

Hierarchy Digital Transmission adopted by CEPT are – – – – – –

E0 E1 E2 E3 E4 E5

64Kbps 2.048Mbps 8.4Mbps 34.3Mbps 139.2Mbs 565.1Mbps

1VC 30E0 4 E1 16E1 64E1 256E1

114

Abis Abis Interface, Interface, Time Time Slots Slots n

n

n

In a manner similar to the air interface, the Abis interface also uses a layered structure, Layers 1, 2, and 3. Though the three layers in the Abis have identical functions to those on the Um interface, their details are somewhat different. Layer 1 on the Abis is also the physical layer on which we find the digital data (speech and signaling) moving between the base station and the BSC at a rate of 2,048 kbps. It makes use of a TDMA structure using 32 time slots, each at a rate of 64 kbps.

115

E1 E1 or or PCM30 PCM30 Link Link n

Due to its structure and speech coding, the 2-Mbps link is also referred to as a PCM3O link. – –

–

TS0

PCM stands for the type of modulation used on Layer 1, pulse code modulation, and the number 30 indicates that out of the 32 time slots 30 are used for user data communication between the base station and its controller. The other two time slots, indicated by the shaded squares in Figure are dedicated to synchronization tasks (on TS 0) and the signaling required between the base station and the BSC simply to maintain Layer 2 of the Abis link (on TS 16).

TS1

.....

TS15

TS16

TS17

.....

TS30

TS31 116

TS TS mapping mapping between betweenAbis Abis and and Um Um TS 0 TS 1

Um

TS 2 TS 3 TS 4 TS 5 TS 6 TS 7

Abis S

T T T T T T T T

16 kbps Subslots

TRX 117

Subslots Subslots in in PCM30 PCM30 n

n

n

TS0

In addition to the allocation of time slots on the 2Mbps frame, the specifications allow a further variation. A 64-kbps channel may be subdivided into four subslots of 16 kbps each. Such a subslot is not only addressed by its time slot number (in the Abis sense), but also by its subslot number. The subslot may be used for signaling purposes or traffic channel assignments. TS1

.....

TS15

TS16

T T T T 1 1 1 1

TS17

.....

TS30

TS31

118

The A interface n

n

n n

n

The A interface is the interface signaling protocol between BSC and MSC. The A interface defines the messages between the BSC and the MSC, and messages to/from MS. Uses 64Kbps E0 channels Uses the SS7 lower layer protocol stack for carriage protocol (MTP and SCCP, to be discussed later) Two message sets are defined for this purpose – DTAP (Direct Transfer Application Part) – BSSMAP (BSS Management Part) – These protocols will be described later

119

Chapter Chapter 1. 1. n n

Introduction, Course Overview and Objectives Review of GSM Protocol – – – –

n

n n n

Spectrum and Physical Channels Frame and Time Slot Structure Logical Channels GSM Coding and Modulations

Network Elements and Architecture – BSS – NSS – OAM Fixed Network Connections Overview of RF network Planning Section Summary and Discussions

120

Network Network Planning Planning n

The problem of planning a wireless network can be formalized as follows: Given – the subscribers’ density and their statistical behavior, – terrain and propagation environment characteristics – and available bandwidth as input data, – minimize the cost of radio and network infrastructure with respect to radio coverage and cell layout, channel reuse and frequency plan, – subject to quality of service constraints.

n

This problem is quite complex and is typically addressed through decomposition. 121

Design Design Considerations Considerations n

Implementation Issues – Cost and Time to Market – Resources – Expansion Provisions

n

Performance Issues – Coverage – Grade of Service – Quality of Service

122

Coverge Coverge Issues Issues n n n n

n n

RF Channel Characterization Receiver Sensitivity Coverage Design Parameters Coverage Simulations and Performance analysis Field Verification Handoff Provisioning

123

Traffic Traffic and and Capacity Capacity Issues Issues n

Subscriber Forecast, – Expected Service Penetration – Subscriber Distribution Maps

n

Traffic Modeling, – – – –

n n n

Traffic Types Access Pattern Average Load per Call Grade of Service

Air Interface Capacity Hardware Limitations Backhaul and Fixed Network Impact 124

Quality Quality of of Service Service Issues Issues n

Inter-cell and Intracell interference Issues in – TDMA Networks – CDMA Networks

n

Interference Management – Interference Avoidance Techniques – Channel Assignment » FCA » DCA

– Interference Cancellation Techniques – Interference Averaging Techniques 125

Design Design Process Process n

n

Network Planning is typically addressed through decomposition. The main steps characterizing the mobile network planning procedure include traffic and mobility model, radio coverage and cell dimensioning, frequency plan, distribution, switching, and signaling and database network planning. – As the planning phases are strictly dependent on each other, an iterative approach is typically used. – – – –

126

RF RF Design Design Preparation Preparation n n n n

RF design Starts with some preparation, Selecting the vendor Setting Design Objectives and Standards Setting up required databases – Terrain, Morphology, Road Maps, Demographics, Client Preferred site locations,

n n

Antenna’s and Hardware related specifications Estimating required Resources – RF engineers (man-hours) – Measurement Tools – Software Tools 127

Predesign Predesign Measurements Measurements n

n

n

Measurement tools should be used to characterize the propagation environment in various areas within the market. Fine tune the parameters of the propagation model used by the software tool; e.g. Correction Factors, path Loss Slope ... Optional ( if time and money restrictions permit) – Penetration Losses (In-building, In-car,..) – Fading and Delay spread statistics. 128

Paper Paper Design Design (LBA) (LBA) n

Link Budget Analysis (LBA) is a spread-sheet type analysis of losses and gains in the forward and reverse radio paths. – – – – –

n

LBA has the following objectives: Estimating Maximum allowable path loss Balancing forward and reverse link foot prints Defining coverage thresholds for various coverage classes determining typical transceiver parameters

LBA also provides us with estimates of cell radius and cell count, which together can define a first cut cell layout.

129

Maximum Maximum RF RF Path Path Loss Loss PABS

Path Loss Down Link

RXMS Sensitivity

PAMS

Path Loss Up Link

RXBS Sensitivity 130

LBA LBA Inputs Inputs n

Base and Mobile Receiver Sensitivity Parameters – Minimum Acceptable Signal to Noise Ratio – Environmental/Thermal Noise Assumption – Receiver Noise Figure

n

n

n n

n

Antenna Gain at Base and Mobile Station Hardware Losses (Cable, Connectors, Combiner,....) Target Coverage Reliability Propagation Characteristics of the Channel Receiving Environment

LBA

131

LBA LBA Outputs Outputs

n

LBA

Coverage Design Thresholds – In-Building – In-Car – On-Street

n n

n n

Base Station ERP Maximum Allowable Path Loss Cell Size Estimate Cell Count Estimate 132

Cell Cell Size/Count Size/Count Estimation Estimation n

Objective: – To determine the size and number of cells required to provide coverage for a given area.

n

Required Input: – Maximum Allowable Path Loss (MAPL) – Propagation Loss Model – Market Boundaries

133

Cell Cell Size/Count Size/Count Estimation Estimation Link Budget Analysis Max Allowable Path Loss

Market Boundaries

Field Tests Path Loss Model

Cell Radius Estimate

Cell Count Estimate 134

Cell Cell Size Size Estimatation Estimatation n

Using Hata’s Empirical Formula PL

=

69.55 + 2616 . log10 f c

−

13.82 log10 hb

+

( 44.9 − 6.55 log10 hb ) log 10 R − a ( hm ) Solve it backward to Cell radius estimate based on Hata’s formula:

MAPL− 69.55 − 2616 . log10 fc + 13.82log10 hb + a(hm ) log10 R = 44.9 − 6.55log10 hb

135

Cell Cell Count Count Estimation Estimation

136

Simulations Simulations & & Implementation Implementation n

n n n

n

Initial Design consists of the following major steps, Coverage Analysis Site Selection considering Capacity Analysis Capacity Analysis Interference avoidance Interference Analysis through careful frequency & planning Frequency Planning These steps usually involve iterations. Implementation – Any change in site configuration to alleviate a capacity or interference problem may violate coverage rules and objectives.

Optimization 137

Radio Radio Coverage Coverage Design Design n

n

For radio coverage and cell dimensioning, the previous traffic data are considered together with the propagation issues. The main factors affecting the electromagnetic coverage forecast are: – Terrain configuration, – Mobility and Fading effects. – Land use, vegetation, and urbanization density – Penetration losses associated with receiving environments, buildings and vehicles.

138

Traffic Traffic Analysis Analysis n n

n

n

As for the traffic modeling, the PCS service area must be characterized based on subscribers' density and distribution. Geographical maps or territorial databases are utilized to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution. In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.

139

Joint Joint Radio Radio & & Traffic Traffic Design Design n

n

In principle radio coverage and traffic distribution are to be considered jointly. However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity requirements deriving from the traffic forecasting.

n

n

These two very strictly dependent steps are iterated until a satisfactory solution is derived. The factors conditioning the resulting cell layout come from either propagation or traffic constraints, depending on the most critical conditions. 140

Frequency Frequency Planning Planning & & FCA FCA n

n

Once the cell layout and the cell dimensioning (in terms of channels) are identified, a frequency plan is to be evaluated by keeping the relevant quality of service above an assigned threshold. A formal description of the frequency planning task in a Fixed Channel Assisgnment (FCA) system follows: – minimize the overall bandwidth (union of used frequencies Fi ) – subject to (C/I)i > (C/I)0 for all i’s. Fi is the set of frequencies assigned to cell i and (C/I) 0 represents the minimum allowed carrier to interference threshold (the quality of service measure). 141

Channel Channel Assignment Assignment n

Channel assignment is the problem of – allocating enough channels or frequencies to each base station to meet its capacity needed, subject to – maintaining a minimum C/I for all points within the service area.

n

The channel assignment can be – Fixed – Semi_fixed – Dynamic

142 142

Fixed Fixed Assignment Assignment n

n

In fixed assignment, channels are permanently allocated to each cell to meet a pre-determined GOS. Fixed assignment can be based on: – Uniform reuse pattern if traffic is uniformly distributed among cells. – Non-uniform based on estimated traffic in each cells coverage area.

Frequency planning is a search for the assignment that causes minimum intercell co-channel and adjacent channel interference. Question: What is Semi-Fix Channel Assignment? n

143 143

Dynamic Dynamic Channel Channel Assignment Assignment n

n

n

In DCA the allocation of channels is changed adaptively according to the dynamics of the call traffic. DCA relies on periodic uplink and/or down link measurements of multiple channels to find the one which causes least amount of interference. DCA maximizes the bandwidth utilization by effectively – maximizing the number of channel reuses and – minimizing the number of idle channels

n

DCA algorithms may be centralized or distributed.

144 144

Implementation Implementation & & Optimization Optimization n

n

n

n

Once all the coverage, capacity and interference objectives are met site acquisition and candidate site evaluation starts. For time and cost considerations, in some design projects client prefers to perform an extensive initial site acquisition and evaluations. System implementation and optimization requires both drive tests and simulations. At this phase iterations on coverage, capacity and interference analysis and frequency plan, similar to previous phase, is performed but now based on real and feasible sites. 145

Chapter Chapter 1: 1: Review Review and and Discussions Discussions

Introduction & Review of GSM Channelization Network Elements & RF Planning

146

GSM GSM Signaling Signaling Protocols Protocols MS

Application

OSI Layers

CC MM RR

BTS

Um Interface

BSC

A-bis Interface

Relay Anchor HLR/ GMSC PSTN/ MSC/VLR MSC/VLR AuC SMS Gateway ISDN A Interface

B Interface

RIL3-CC

C,D Interface

MAP/D

MAP/C

RIL3-MM RIL3-RR

RSM

BSSMAP

TUP ISUP

MAP/E MAP/G

Presentation Session Transport

Network Data Link LAP-Dm Physical Radio

LAP-D CEPT0

SCCP

SCCP

SCCP

SCCP

MTP3

MTP3

MTP3

MTP3

MTP3

MTP2

MTP2

MTP2

MTP2

MTP3

MTP1

MTP1

MTP1

MTP1

MTP1

147

Functional Functional Planes Planes Operator n

n

n

In the telecommunications domain. a powerful method to obtain a functional grouping is to use the Open System Interconnection model. Functions are grouped in functional planes, represented as stacked one upon the other. The lowest plane, devoted to the physical transmission of information between distant entities, relies on physical hardware media. whereas the highest one represents the view of external users. Each plane (or layer) provides services to the next layer up, these services being themselves enhancements of the services provided by the next layer below.

OAM

User

CM MM RR

Transmission

148

Transmission Transmission n

n

n

At the bottom lies the basis of any telecommunications system, i.e. the transmission plane. It provides transmission means for the communication needs of the users as well as for information transfer between the co-operating machines. Transmission layer includes both physical and link layer functionalities. Transmission is a domain for very short time scale events. from microseconds (e.g.. bit modulation) to seconds (for message transmission).

Operator

OAM

User

CM MM RR

Transmission

149

Transmission Transmission (cont.) (cont.) n

Some of the GSM machines are concerned with transmission only. – An obvious example is the transcoder and rate adapter unit (TRAU). which is only concerned in adapting speech or data representations. – But most other transit exchange machines also play a more or less complex role in transmission. The mobile station obviously does so, and so does the BSC. the MSC and the interworking function (IWF) which may all be along the transmission path between two users. – Conversely. some of the machines have no relation to transmission except for the minimum needs concerning signaling with the other machines. These include the data bases (HLR. VLR. EIR and the OSS in general. 150

Operator

User

Radio RadioResource ResourceManagement Management OAM CM MM RR Transmission n

n

n

The next plane up is concerned with the management or transmission resources. The RR layer provides stable links between the mobile stations and the MSCs coping in particular with the movements of the users during the call (handovers). In telecommunications networks, these functions are usually grouped with the communication management functions, because fixed circuit management represents a small portion thereof. However, in the case of a cellular system such as GSM. the management of transmission resources on the radio path is a complex issue and it warrants its own functional plane. From a temporal point of view this plane and the two next ones deal with events on the scale of the call; that is to say from seconds to 151 minutes.

Operator

User

Mobility Mobility Management Management OAM

CM MM RR Transmission n n

n n n

Next comes a small functional plane. which has not been grouped with communication management because of its strong GSM specificity. This Mobility Management layer or MM layer.is in charge of managing subscriber data bases and in particular the subscriber location data. An additional task of the MM layer is the management of confidentiality aspects such as authentication. The SIM, HLR and AuC are examples of machines mostly involved in MM activities. The MM layer adds to the transmission functions provided by the lower layers the means to track mobile users when not engaged communication. and the security related functions. 152

Operator

User

Communication CommunicationManagement Management OAM CM MM RR n

Communication Management (CM)

Transmission

» The next plane is much less specific to GSM. It makes use of the stable basis provided by the RR and MM layers to provide telecommunications services to the users. » CM layer consists of several independent components, depending on the type of service. » The NSS, mainly the MSC, has a strong involvement in the CM layer. n

The variety of the Communication Management functions makes it easier to describe as three subdomains. » Call Control (CC) » Supplementary Services Management (SS) » Short Message Services (SMS)

153

CM ---CC CM---CC n

n

n

The MSC/VLRs, GMSCs, IWFs and HLRs through basic call management functions are able to manage most of the circuit oriented services provided to GSM users including speech and circuit data. This functional core represents a sub-part of the CM layer and is called Call Control (CC) in the specifications. An important aspect of communication management beside establishing, maintaining, and releasing calls is the routing function i.e. the choice of transmission segments linking distant users and their concatenation through switching entities. GSM mostly relies on external networks to perform this task, interfacing these networks through MSCs and GMSCs. 154

CM ---SS Mangement CM---SS Mangement n

n

n

Users in GSM have some control on the way their calls are handled by the network. This capability is described as supplementary services, each one of them corresponding to some specific variation of the way the basic service is rendered to the user. The entities involved in SS management are very few: the mobile station and HLR are the only entities involved

155

CM ---SMS CM---SMS n

n

n

The last aspect of the CM layer is related to the point-to-point short message services (SMSPP). For the purpose of these services GSM is in contact with a Short Message Service Center (SM-SC). A service center may be connected to several GSM networks. In each of these one or several functional entities are in charge of interfacing the SM-SC. They are basically gateway functions. 156

Operator

User

OAM OAM OAM

CM MM RR Transmission n

Operation, Administration and Maintenance (OAM) – The OAM plane includes the functions which enable the operator to monitor and control the system. » In one direction, it mediates the observation flow from machines to the operator. » In the other direction, it enables the operator to modify the configuration of machines and functions ..\s a functional plane, it hovers over all the others. whilst not using the services provided by the other planes except the basic transmission functions for the exchanges between the concerned machines.

157

Who Who is is involved involved in in OAM OAM Plane Plane n

n

n

The kinship between the OAM plane and the OSS is obvious. The OSS is an integral part (if the OAM plane. but all the machines in the BSS and the NSS also contribute to the Operation and Maintenance functions. There are a variety of small tasks incumbent on these machines: they are often those of the smallest time scale and scope. For instance : – the raw information which forms the basis for the observation of the system behavior is clearly issued inside the traffic handling machines themselves. The data are then transferred to OSS machines.

158

Signaling Signaling types types In-Band

Voice Channels (Trunk Group)

Out-of-Band: Associated

Signaling Channel

Associated Out-of-Band: Quasi-Associated

Asso ciate d Quasi-Associated

Out-of-Band: Disassociated STP 159

Network Network Signaling Signaling Types Types n

In-Band – Network signaling and speech share the same physical channel (e.g., trunk circuit). – Limited by long setup times and minimal data transfer (e.g., dialed digits, ANI, CIC). – End-to-end setup of voice circuit necessary before determining if destination party is reachable.

n

Out-of-Band: Associated – Network signaling and speech are on separate physical channels. – Signaling, between switching offices, follows the same path as the voice channels. – Benefits include shorter setup times and the ability to transfer more data, quickly. – Not necessary to setup voice facilities, only to findout that end party is unreachable 160

Network Network Signaling Signaling Types Types (cont.) (cont.) n

Out-of-Band: Quasi-associated – Network signaling and speech are on separate physical channels. – Signaling may, but does not have to, follow the same path as the voice channels it supports. – Unlike non-associated, the path taken by quasi-associated messages is fixed.

n

Out-of-Band: Disassociated – Network signaling and speech are on separate physical channels. – Signaling and voice channels are on two, completely separate networks. – All the Out-of-Band benefits, plus additional benefits with an independent data network. 161

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP Recap of GSM Protocols and Interfaces GSM Call Flows and Short Message Subsystem Summary and Discussions 162

OSI OSI Layers Layers Open Systems Interconnection (OSI) Reference Model for Data Communications Created in the late 1970’s by the International Standards Organization (ISO)

7 - Application

Application

6 - Presentation

Presentation

5-

Session

Session

4 - Transport 3 - Network

Transport Network

Network

2-

Link

Link

Link

1-

Physical

Physical

Physical

End User

End to End Layers

Packet Switch

Chained Layers

End User 163

Headers Headers and and Layers Layers

Application Presentation Session Transport

Data Proto col C ontro l info rmati on(PC I)

Data

Application Presentation Session Transport

Network

Network

Link

Link

Physical

Physical 164

Layer Layer 11 & & 22 n

Layer 1 - Physical – Defines the mechanical and electrical aspects of the transmission medium - evervthing needed to transfer bits between two adjacent devices.

n

Layer 2 - Link – Specifies the protocol that will provide for error-free transmission of messages between adjacent nodes. It is a point-to-point protocol – Takes the Layer 3 user info and encases it with a header and/or trailer before sending it to the Layer 1 protocol (and vice-versa).

165

Layer Layer 33 n

Layer 3 - Network – Specifies the protocol that will (1) address messages and (2) route them from end-to-end across any number of subnetworks. – Takes the Layer 4 user info and appends its own Protocol Control Information (PCI) before sending it to Layer 2 (and vice-versa).

166

Layer Layer 44 n

Layer 4 - Transport – Specifies the protocol that will provide endto-end control of the communications. Provides end-to-end error recovery and flow control. – The size and complexity' of the layer 4protocol depends on the reliability of layer 3 protocol to sequentially deliver messages error-free.

167

Layers Layers 5, 5, 66 & & 77 n

Layer 5 - Session – Specifies the protocol that will provide process-toprocess control of the communications. – Establishes, manages. and terminates connections (sessions) between applications.

n

Layer 6: Presentation – Performs a transformation on data so that a standardized application interface (video screen. Printer. etc.) can be provided.

n

Layer 7 - Application – Provides services to the network users. 168

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP GSM Call Flows and Short Message Subsystem Recap of GSM Protocols and Interfaces Summary and Discussions 169

GSM GSM Signaling Signaling Protocols Protocols MS

Application

OSI Layers

CC MM RR

BTS

Um Interface

BSC

A-bis Interface

Relay Anchor HLR/ GMSC PSTN/ MSC/VLR MSC/VLR AuC SMS Gateway ISDN A Interface

B Interface

RIL3-CC

C,D Interface

MAP/D

MAP/C

RIL3-MM RIL3-RR

RSM

BSSMAP

TUP ISUP

MAP/E MAP/G

Presentation Session Transport

Network Data Link LAP-Dm Physical Radio

LAP-D CEPT0

SCCP

SCCP

SCCP

SCCP

MTP3

MTP3

MTP3

MTP3

MTP3

MTP2

MTP2

MTP2

MTP2

MTP3

MTP1

MTP1

MTP1

MTP1

MTP1

170

LAPD LAPD (Link (Link Access Access Protocol Protocol D) D) n

n

n n

n

n

n

Is the interface protocol between the BTS and BSC Abis link layer Is a link layer protocol for a point-to-multi-point connection Is the ISDN link layer protocol defined by Q.921 standard. Each frame contain an address identifying the source and destination Is the HDLC based protocol and has the same frame structure as HDLC Provides the same benefits as HDLC based protocols (ensures error free transmission) Provides reliability, efficiency and hierarchical independence. 171

LAPD LAPD Frame Frame Format Format FLAG ADDRESS CONTROL INFORMATION FCS FLAG 8 bits

n n n n n n n n n

8 bits

8 bits

N bits (260 bytes)

16 bits

8 bits

Flag: The bit sequence 01111110 constitute a frame boundary. Adjacent frames can be separated by single flags. Address: contains the Service Access Point identifier(SAPI) range from 0-63 and Terminal Endpoint Identifier(TEI) range from 0-127. Control: Indicates the frame types and frame sequence. Information: Data(only present in I and FRMR frames) FCS: The frame check sequence detects corruption due to random or burst line errors. FCS insertion and control is performed traditionally by the hardware. The FCS is a polynomial of the form 172

LAPDm LAPDm Frame Frame Format Format n

n

n

It is the protocol that used by the Um interface between the MS and BTS. It is similar to LAPD protocol but with different frame format. LAPDm frame format ADDRESS CONTROL 8 bits

8 bits

INFORMATION 21 to 23 bytes

173

LAPD LAPD and and LAPDm LAPDm differences differences n

A few differences in each functional area are: – Segmentation and Re-assembly function » LAPDm frame length are 21(TCH) to 23(SACCH) octet, it may be too short for a complete message » LAPD frame size is 264 octets no need for segmentation

– Error detection and correction » No flags are between LAPDm frames. A length indicator and a filler value (00101011 or 11111111) is included by LAPDm » No CRC checksum in LAPDm (The radio insures error free transmission) » Sequencing of Modulo 8 used by LAPDm, LAPD uses 128

174

LAPD/ LAPDm Differences LAPD/LAPDm Differences (cont.) (cont.) » Window size of 1 (send and wait) is used by LAPDm, LAPD uses variable window size of 1 - 8. » The LAPDm link initialization can contain data (SABM, UA, piggy backed data) but LAPD does not allow piggy back on initialization frames. » Multiplexing » LAPDm is address field only contains SAPI. » SAPI 0 for signaling and SAPI 3 for SMS on LAPDm » SAPI 62 operation and maintenance, SAPI 63 Layer 2 management

– Flow Control » RNR and REJ frames are not supported on LAPDm No stop-go procedure 175

X.25 X.25 n

n n

ITU(formerly CCITT) Recommendation that defines the interface between the user (DTE) and the Network (DCE) for user data packets. – Based on the OSI layered protocol defined by ITU (CCITT x series) and ISO. – Protocols are defined for physical(layer 1), link(layer 2) and network(layer 3). – Provides error free link, flow control and routing capability. Most reliable data transfer method. Frames based on High level Data link Control(HDLC) The GSM OMC interface to NSS elements uses X.25 protocol. 176

X.25 X.25 3-

Network

Network

Network

2-

Link

Link

Link

1-

Physical

Physical

Physical

DTE n

n

n

DCE

DTE

The Layer 1 protocol deals with the electrical, mechanical, procedural, and functional interface between the subscriber (DTE), and the base station (DCE). The Layer 2 protocol defines the data link on the common air-interface between the sub-scriber and the base station. Layer :3 provides connection between the base station and the MSC, and is called the packet layer protocol. A packet assembler disassembler (PAD) is used at Layer :3 to connect networks using the X.25 interface with devices that are not equipped with a standard X.25 interface. 177

X.25 X.25 Link Link layer layer frames frames n

The message types are: Frame type

» Information frame I frames » Supervisory frames (S-frame) • Receive Ready • Receive Not Ready • Reject

RR RNR REJ

Command/Response

C

C/R C/R C/R

» Unnumbered frames(U-frame) • Disconnect • Disc Mode • Frame Reject • Sync balance • Unnumbered Ack C = Command frame R = Response frame

DISC DM FRMR SABM UA

C R R C R

178

Network/Packet Network/Packet layer layer n

n

n

n n n

Perform packet data switching, routing and recovery Supports permanent virtual circuits (PVC) and switched virtual circuits(SVC) Perform Flow control and call control (tear down and establishment). Assembly and disassembly of the packets. Retransmission and error recovery Support of extended sequence number modulo 128 and modulo 8. 179

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP Recap of GSM Protocols and Interfaces GSM Call Flows and Short Message Subsystem Summary and Discussions 180

What What is is SS7 SS7 n

n

n n

n

Signaling System No 7 is the ITU (formerly CCITT) standard that defines the communications protocol layers required to perform the call control signaling function. It is a synchronous protocol that performs the call control and transaction capabilities function for the GSM. It is designed based on the packet network technology. It is designed to operate on a separate network than the voice and user data network. There are several versions of SS7 standards including – CCITT International Telegraph and Telephone Consultative Committee, which operates under ITU – ANSI, American National Standard Institute – BellCore 181

SS7 SS7 Network Network Elements Elements n

Signaling Transfer Point (STP) – Is a stand-alone switch that relays SS7 messages from one signaling link to another. – For reliability purposes STPs are installed in pairs (mated). – Each STP can completely take over for its mate without any performance degradation.

n

Signaling Point (SP) – Is a switching system that interconnects input devices (e.g. telephones, service terminals) with the SS7 Network. – SP is able to originate call control messages only. 182

SS7 SS7 Network Network Elements Elements n

Service Switching Point (SSP) – Is also a switching system that interconnects input devices with the SS7 network. – SSP is able to originate database queries in addition to call control messages.

n

Service Control Point (SCP) – Is database that accepts queries and provides responses over the SS7 network – For reliability purposes SCP’s are installed in pairs (mated). – Example services: l-800, Line Information DataBase (LIDB). Home Location Register (HLR). 183

SS7 SS7 Network Network E

STP

STP

MSC

STP

B A

B C

C STP

F

A

STP

C

SP F

STP

PSTN

MSC

D STP C

A

HLR

STP

HLR

184

SS7 SS7 Links Links n

A-Link: Access Link – Connect SP / SSP / SCP to the home STP pair. Deployed in a pair arrangement - at least one link to each STP. For Example The MSC and HLR interface to SS7 network use the A-link.

n

B-Link: Bridge Link – Connect an STP pair to another STP pair, which is in the same SS7 network.Deployed in a quad arrangement - four paths provided from each STP to the other STP pair.

n

C-Link: Cross Link – Connect STP to its mate. 185

SS7 SS7 Links Links n

D-Link: Diagonal Link – Connect an STP pair to another STP pair, which is NOT in the same SS7 network. Deployed the same as B-Links.

n

E-Link: Extended Link – Connect SP / SSP / SCP to a non-home STP or STP pair.

n

F-Link: Fully Associated Links – Connect SP / SSP / SCP to another SP /SSP / SCP, directly. For example the MSC to BSC interface use the F-link configuration.

186

Link Link Elements Elements Link set Combined Link Set

Link 00 SLC 01 SLC 02 SLC

SP/SSP

A Route Set Is an ordered list of combined linkset or link sets. In a given system each destination node or group of nodes is assigned a route set. The route set is accessed when determining which linkset should carry a message to a node.

SLC SL 00 C0 1 SLC

02

187

SS7 SS7 and and OSI OSI OSI model 7 Application 6 5 4

Presentation Session

SS7 Protocol Model OMAP ASE

TCAP

ISUP

ISP

Transport

3

Network

2 1

Link Physical

SCCP MTP Level 3 MTP Level 2 MTP Level 1

188

Network Network Service Service Part Part (NSP) (NSP) n

n

n

The NSP provides ISDN nodes with a highly reliable and efficient means of exchanging signaling traffic using connectionless services. The SCCP in SS7 actually supports packet data network interconnections as well as connection-oriented networking to virtual circuit networks. The NSP allows network nodes to communicate throughout the world without concern for the application or context of the signaling traffic.

OMAP ASE

TCAP

ISUP

ISP SCCP MTP Level 3 MTP Level 2 MTP Level 1

189

Message Message Transfer Transfer Part Part n

The function of the MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end-users and the network.

n

MTP is provided at three levels with various functionalities. User Message Processing Common Transfer Function

User Message Processing

Signaling Link

Link Control Functions

Signaling Data Link

Link Control Function

Message Transfer Part

Common Transfer Function 190

MTP MTP Level Level 11 n

n

Signaling data link functions (MTP Level 1) provide an interface to the actual physical channel over which communication takes place. CCITT recommends that MTP Level 1 use 64 kbps transmissions, whereas ANSI recommends 56 kbps. The minimum data rate provided for telephony control operations is 4.8 kbps. User Message Processing Common Transfer Function

User Message Processing

Signaling Link

Link Control Functions

Signaling Data Link

Link Control Function

Message Transfer Part

Common Transfer Function 191

MTP MTP Level Level 22 n

n

Signaling link functions (MTP Level 2) correspond to the second layer in the OSI reference model and provide a reliable link for the transfer of traffic between two directly connected signaling points. MTP Level2 also provides flow control data between two signaling points as a means of sensing link failure. User Message Processing Common Transfer Function

User Message Processing

Signaling Link

Link Control Functions

Signaling Data Link

Link Control Function

Message Transfer Part

Common Transfer Function 192

MTP MTP Level Level 33 n

n

Signaling network functions (MTP Level 3) provide procedures that transfer messages between signaling nodes. As in ISDN, there are two types of MTP Level 3 functions: signaling message handling and signaling network management. User Message Processing Common Transfer Function

User Message Processing

Signaling Link

Link Control Functions

Signaling Data Link

Link Control Function

Message Transfer Part

Common Transfer Function 193

SCCP SCCP n

n

n

n

Signaling Connection Control Part (SCCP) is a layer on top of MTP layer 3. It provides enhancement to the addressing capabilities provided by the MTP. While the addressing capabilities of MTP are limited in nature, SCCP uses local addressing based on subsystem numbers (SSNs) to identify users at a signaling node. SCCP also provides the ability to address global title messages, such as

OMAP ASE

TCAP

ISUP

ISP SCCP MTP Level 3 MTP Level 2 MTP Level 1

800 numbers or non billed numbers. 194

SCCP SCCP n

SCCP is mainly used by the GSM A interface and provides global title translation function for the NSS. – Connection oriented » The messages are not directly related to a single mobile » Reset or overload indications

– Connection less oriented » Separate independent connection for each MS » To distinguish transaction for each MS » The connections are established on the needed bases by the BSC or MSC and release when the transactions complete.

195

SS7 SS7 User User Part Part n

The SS7 User Part provides call control and management functions and call set-up capabilities to the network.

n

These are the higher layers in the SS7 reference model, and utilize the transport facilities provided by the MTP and the SCCP. – – – –

The SS7 user part includes ISDN User Part(ISUP). Transaction Capabilities Application Part (TCAP) Operations Maintenance and Administration Part (OMAP). 196

ISDN ISDN User User Part Part (ISUP) (ISUP) n

n

n

n

The Integrated Services Digital Network User Part (ISUP) provides the signaling functions for carrier and supplementary services for voice, data, and video in an ISDN environment. In the past, telephony requirements were lumped in the TUP, but this is now a subset of ISUP. ISUP uses the MTP for transfer of messages between different exchanges. concerned with remote operations. TCAP messages are used by IS-41. 197

SS7 SS7 ISUP ISUP Responsibilities OMAP

Control circuit-switched connections between line exchanges. Provide Basic Bearer & Supplementary Services

ASE

TCAP

ISUP

ISP SCCP

Basic Bearer Services Call Setup Connection Call Release

Supplementary Services

MTP Level 3

Redirection of Calls

MTP Level 2

Malicious Caller Identification Calling Line ID Identification

MTP Level 1

Called Line Identification Closed User Groups Completion of Calls to Busy Subscriber 198

TCAP TCAP n

n

n

The Transaction Capabilities Application Part (TCAP) in SS7 refers to the application layer which invokes the services of the SCCP and the MTP in a hierarchical format. One application at a node is thus able to execute an application at another node and use these results. Thus, TCAP is concerned with remote operations.

OMAP ASE

TCAP

ISUP

ISP SCCP MTP Level 3 MTP Level 2 MTP Level 1

199

TCAP TCAP (cont.) (cont.) n n

Transaction Capabilities Application Part envelopes the mobility messages Provides the means to distinguish independent message flows – The transaction sub-layer ties the messages in a dialogue and performs transaction management (begin, continue, end ..) – And the component sub-layer handles the command /response of a dialogue. (Invoke, return result, reject) 200

TCAP TCAP in in MAP MAP and and IS41 IS41 n

Two types of Mobile application signaling takes advantage of TCAP – Mobile Application Part MAP, GSM DCS1800 and DCS900. MAP defines the interfaces between different component in the GSM, (MSC <-> HLR, MSC<->MSC) – IS41 Interim Standard 41 the TIA (U.S standard) and recently introduce as the ITU-R standard. This standard defines the interfaces between different component (MSC<->HLR, MSC<->MSC etc.)

201

OMAP OMAP n

n

Operation Maintenance and Administration Part (OMAP) functions include monitoring, coordination, and control functions to ensure that trouble free communications are possible. OMAP supports diagnostics are known throughout the global network to determine loading and specific subnetwork behaviors.

202

Mobile Mobile SS7 SS7 network network elements elements n

n

n

n

The MSC is connected to both STP via A quad links. Each link (logical) run at 40% utilization. STPs are connected via the C link and A quad links to PSTN to avoid a single point of failure within a network. The SCP/HLR is also connected via A quad links to STPs. The PSTN to MSC is connected via the F link. ISUP application is used on these types of links. 203

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP Recap of GSM Protocols and Interfaces GSM Call Flows and Short Message Subsystem Summary and Discussions 204

Mobile Mobile Application Application Part Part n n

All non-call-associated signaling in GSM is grouped under MAP. Non-call-associated signaling implies all signaling dealing with – mobility management, – security, – activation/deactivation of supplementary services, and so on.

n

All protocols use SS7 lower three layers (i.e., MTP 1,2,3, SCCP layer, and TCAP layer). These protocols are used primarily for database queries and responses. 205

MAP MAP Protocol Protocol Connections Connections BSSMAP BSS

MAP/F

MSC

EIR

MAP/B MAP/I VLR

HLR

MAP/D RIL3

MAP/G MAP/C MAP/E

GMSC

MAP/C

VLR MAP/B MSC

MAP/H

SMS Gateway 206

MAP -B MAP-B n

MAP-B is the interface between the MSC and its associated VLR. – Whenever the MSC needs data related to a given mobile station currently located in its area, it interrogates the VLR. – When a subscriber activates a specific supplementary service or modifies some data attached to a service, the MSC informs (via the VLR) the HLR that stores these modifications and updates the VLR if required. – This interface between the MSC and the VLR is very heavily used, and hence the decision by several manufacturers to integrate the VLR functionality with the MSC.

207

MAP -C MAP-C n

MAP-C is the interface between the MSC and the HLR. – The gateway MSC queries the corresponding subscriber HLR to determine the routing information for a call or a short message directed toward the user. This messaging is handled by the MAP-C protocol. Additional SMS and charging messages also form part of this interface message set.

208

MAP -D MAP-D n

MAP-D is the interface between the HLR and the VLR. – It is used to exchange data related to the location of the mobile station and for the management of the subscriber. – The VLR informs the HLR of the location of a mobile station managed by the latter and provides it with the roaming information for that subscriber. – Exchanges of data may occur when the mobile subscriber requires a particular service, when changes to the subscription have to be done, or when some parameters of the subscription are modified by administrative means. 209

MAP -E & -F MAP-E & MAP MAP-F n

MAP-E – This interface supports the necessary signaling support for the handover function. – When a short message is to be transferred between a mobile station and short message service center, this interface is used to transfer the message between the MSC serving the mobile station and the MSC acting as the interface to the message center.

n

MAP-F – is the interface between the MSC and the equipment identity register (EIR). – It is used to exchange data to enable the EIR to verify the mobile subscriber equipment 210

IS -41 IS-41 n

n

n

It is a US standard that defines the intersystem operation that was develop by TIA, which is becoming an ITU-R standard. First revision in 1983 IS-41 Rev 0 only addressed Intersystem HO. Future revisions A,B,C and D addresses the following issues: – Automatic Roaming and call delivery in addition to – To add new subscribers features to the standardized set – To add functionality to support new network requirements (IN and digital networks) – To add clarification and remove errors

211

IS -41 C IS-41 C Model Model MSC

EIR F

M S

Ai

MSC

A

BS

PSTN

E

C

Di

H

AUC

HLR

ISDN

B D

VLR

Q

N

SME

M

SME

M

MC

All interfaces in bold are IS41C

M

MC

212

IS41 IS41 Architecture Architecture n n

n

n

n n

The signaling backbone is based on SS7 protocol It uses the MTP layer 1,2 and 3 the SCCP connectionless protocol and TCAP layer Provides mobile application part MAP functionality (MM, CM and RR) but incompatible with GSM MAP. Supports the air interfaces of AMPS/NAMPS and CDMA IS-95/IS136(800, 1900MHZ) Supports the MSC/BS interface IS-634 and IS-653 Support SMS and Authentication functionality 213

IS -41 and -working ?? IS-41 and GSM GSM inter inter-working n

n

n

Inter-working means the Mobile Application Part successful communications It requires an inter-working function IWF, a device that coverts protocols as well as performing database mapping There are market drivers, I.e international roamers and national roamers that uses a GSM based network (PCS 1.9)

214

FYI: FYI: Addressing Addressing and and Routing Routing n

Within the GSM network two types of routing can be described – SS7 addressing and message signaling routing – Call Control /number routing

215

SS7 SS7 addressing/routing addressing/routing n

As previously discussed the SS7 MTP layer 3 provides the routing function. – This layer is used to route within a local network using the Signaling Point Code (OPC and DPC) addressing. Considering the OPC and DPC is known to each element. – The routing is performed using the mapping of the DPC to a physical location (port).

n

n

To interconnect all the local networks or the national SS7 networks the SCCP Global Title Translation (GTT) functionality is used. This SCCP functionality allows a centralized network to hold and maintain all the addresses and routing tables, centralizing the routing function. 216

GTT GTT n

n

n

Global Title Translation is one of the strong routing capabilities of SS7 SCCP layer. For an MSC to send a message to a particular HLR, the MSC does not need to know each Mobile’s HLR point code. Only the adjacent STP point code and the dialed digits (MSISDN) needs to be provided to the STP in order to route the message to the HLR. The STP will perform the translation of the Dialed digits to physical point code (HLR or MSC etc.) 217

Example Example of of GTT GTT Routing Routing STP performs GTT IMSI or MSISDN to HLR point code A-links B-links STP

HLR

A-links MSC/VLR

SS7 Network B-links

STP HLR

Gateway network Alias point code Local SS7 network

SS7 Message from MSC/VLR SCCP Called address = IMSI or MSISDN MTP DPC = STP alias point code

218

GTT GTT (cont.) (cont.) n

n

The STP pair after checking the SCCP header information will determine the message requires GTT translation. It will then extract from the calling number address field in the SCCP header the IMSI of the subscriber and from a database table determines the HLR point code where the validation/authentication should be sent. As can be seen this will eliminate book keeping on every MSC and centralizes the routing/translation on the SS7 STP network.

219

Call Call control control and and number number routing routing n

Two basic number routings are: – Routing of Mobile Terminating Calls (MTC) – Routing of Mobile Origination Calls (MTO)

220

Routing Routing of of MTC MTC

HLR

GMSC MS

RN

MSRN

M

SR

N

PSTN ISDN

I M S I

n

A land line calling party dial the GSM mobile directory number (MS ISDN number) the PSTN after performing the digits translation routes the call to the home PLMN GMSC. The GMSC contains either the routing tables to relate the MSISDN number with the corresponding HLR, or if the GMSC is connected to the SS7 network with the GTT functionality, theSS7 network will identify the HLR.

M SI SD N

n

VMSC

221

Routing Routing of of MTC MTC n

n

n

n

Once the GMSC interrogate the HLR with the MSISDN number, the HLR determines the IMSI from MSISDN number. Note the HLR stores the subscriber’s information based on IMSI not MSISDN. The HLR locates the visiting MSC/VLR point code and if an MSRN available it will return the information to GMSC. If the HLR does not have the MSRN for the subscriber it will request one from the visiting MSC/VLR. The latter can be done via GTT if an SS7 backbone with GTT (IMSI to point code) functionality is available/supported. The GMSC once it receives the MSRN and the MSC/VLR point code it will route the call to the VMSC/VLR. The MSC/VLR will then page the subscriber. 222

Routing Routing of of MOC MOC n

n

n

The call originating information including the dialed digits will be send to the MSC/VLR. The MSC/VLR with the subscriber's profile information performs digits translation (if supported) and routes the call either to the PSTN or to other MSCs (if a MTM call within the network) . If the MSC can not perform the digits translation it would route the call to GMSC for translation and routing. 223

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP Recap of GSM Protocols and Interfaces GSM Call Flows and Short Message Subsystem Summary and Discussions 224

Protocols Protocols and and Interfaces Interfaces SS

HLR

MM+CM

MSC VLR

RR

BSC BSC Air Interface n

n

BTS

Abis Interface

A Interface

The distinction between an interface and a protocol is important. An interface represents the point of contact between two adjacent entities, and as such it can bear information flows pertaining to several different pairs of entities. i.e. several protocols. Signaling messages pertaining to a given protocol may be visible on several interfaces along their path. if the corresponding peer entities are not adjacent. The protocol then appears on several interfaces.

225

GSM GSM Network Network Interfaces Interfaces n

n

n

GSM has created a set of standard interfaces which allows an open system architecture. An operator can mix and match different vendors' equipment as elements in the network. Previously, each vendor had a closed system and each element was proprietary and restricted to the vendors equipment. In GSM it is possible for an operator to choose the BSS (BSC and BTS) from one vendor, the MSC and VLR from another, and the HLR from still another. Interworking is simpler due to the standardized interfaces among all of these entities. 226

Air Air Interface Interface (Um) (Um) n

n

n

n

The radio interface between the BTS and the mobile station is known as the air interface or Um (user interface-mobile). The radio interface uses RF signaling as the layer one and modification of integrated digital services network (ISDN) protocol as layers two and three. This interface has been very well documented in the GSM standards and all mobile station and BTS vendors adhere to it strictly. Each RF channel on the air interface is broken down into time slots wherein mobile subscribers can transmit information. 227

A -bis Interface A-bis Interface n

n

n

A-bis interface is the interface between the BTS and the BSC. All the connections from the BSC to the BTS utilize a modification of ISDN signaling for layer three and use ISDN signaling for layer two. The physical interface is an E1. Since speech is compressed in GSM, each 64-kbps channel on the El supports four TDMA time slots (i.e., four users). There is a separate signaling channel used for control of the BTS that is also transported via an El time slot. 228

A A Interface Interface n

n

n

The A interface uses SS7 for the lower three layers to transport modified ISDN call-control signaling. The information carried on this interface pertains to management of the BSS, call handling, and mobility management. The SCCP and MTP layers provide for data transport. SCCP is implemented in two classes-0 and 2. – Class 0 (connectionless) is for messages for the BSC, – while class 2 (connection oriented is for messages to a particular mobile station or logical connection.

n

BSSMAP controls base-station functions and manages the physical connection between the BSS and the MSC. It also controls allocation of radio channels and intra-BSS handover. 229

The The A A interface interface n

Two message sets are defined – DTAP (Direct Transfer Application Part) » These are messages between MS and MSC.

– BSSMAP (BSS Management Part) » The messages between the BSC and MSC » The BSSMAP messages originates or end in BSC. n

n

The distribution of the messages are performed by a distribution function on top of SCCP. The distribution function will add a header on top of application message to indicate DTAP or BSSMAP. 230

PSTN PSTN Interfaces Interfaces n n n n n

These are the interfaces between the MSC and the PSTN. All of these protocols are grouped under callassociated signaling. T hey are not specific to GSM and are commonly used in PSTNs for call setup. The GSM architecture is based on ISDN access and as such the MSC is based on an ISDN switch. To take full advantage of all the ISDN services the MSC should be connected to the PSTN via CCS7based protocols such as ISUP. 231

GSM GSM Protocols Protocols n

n

Using the OSI model, the GSM system can be described by considering several functional layers arranged in hierarchical form. These consist of the physical layer, data link layer, and the so-called “Layer 3” Layer 3 functions are designated as the application layer and should not be confused with the standard layer 3 functions of the OSI model.

232

Layer Layer 1: 1: Physical Physical Layer Layer n

The lowest layer of the radio interface, layer 1, provides functions necessary to transfer bit streams on the physical radio links. – Digital signal processing techniques are used to perform equalization functions that recover transmitted bit patterns from signals distorted by the radio environment and channel coding functions (due to band limiting) that multiplex signaling and data channels onto the radio path, providing a level of immunity to errors. – Speech coding functions also use complex digital signaling techniques to compress speech information into a manageable data rate and vice versa. 233

Layer Layer 22 n

Layer 2 provides a reliable dedicated signaling link connection between the MS and the BS. – The layer 2 protocol is based on the ISDN link access procedure (LAP-D) but adopted to take account of the limitations using a radio path. On the other hand, standard LAP-D protocol is used internally within BSS (between BTS and BSC). – The Message Transfer Part (MTP) of SS7 is used on the BSC-to-MSC interface to provide a reliable data link service. – The same protocol (MTP1) is kept between MSCs, between MSC to HLR/AUC, AUC to GMSC, as well as between GMSC and PSTN. 234

Layer Layer 33 n

n

n

The application layer is composed of three sublayers: RR, MM, and CM. The RR, together with the data link layer and the physical layer, provide the means for point-to-point radio connections on which MM and CM messages are carried. The overall objectives of layer 3 are to provide the means for the following. – The establishment, operation, and release of a dedicated radio channel connection (RR); – Location update, authentication, and TMSI reallocation (MM); – The establishment, maintenance, and termination of a circuitswitched call(CCM); SS support; SMS support

235

RR RR Protocols Protocols n

The RR protocol entity provides control functions for the operation of common and dedicated channels. – The RIL3 RR protocols establishes and releases radio connections between the MS and various BSCs for the duration of a call and, despite user movements, provides system information broadcasting, inter- and intracell change of channels, and ciphering mode setting, for example. – The Radio Subsystem Management (RSM) protocol provides RR functions between the BTS and BSC. » The Direct Transfer Application Part (DTAP) protocols provide RR messages between the MS and MSC. » The BSS Management Application Part (BSSMAP) protocols provide RR messages between the BSC and MSC. The distinction between DTAP and BSSMAP is provided by a small “Distribution" protocol below them. 236

MM MM Protocols Protocols n

n

n

Mobility management, which best defines the dialog between MS and the network, deals with the management of MS location and the security functions authentication and ciphering key management) necessary for mobile application. In addition to these functions, the MM sublayer also provides connection management services to the CC layer. The higher layer that sits over MM is called the CM. The CM protocol controls the end-to-end call establishment (both mobile originating and terminating) and, in general, all functions related to call management.

237

Other Other Protocols Protocols n

n

n

n

In addition to the aforementioned protocols, there are other protocols such as MTP3 and SCCP that are used above the data link layer between BSCs and MSCs and also between MSCs and different databases. TCAP protocol, which sits above SCCP, supports various transactions between two nodes of the network. TCAP manages the transaction on an end-to-end basis. MAP protocol is used between MSC, VLR, HLR, and AUC in the form of query and response messages. These protocols are designated as MAP/B through MAP/H.

238

Chapter Chapter 22 n

Overview of protocols and interfaces – Functional Planes – Basic Signaling Concepts and OSI (review)

n

GSM Interfaces and Protocols – LAP-D and LAP-Dm – X.25 Signaling – SS7 Signaling Network

n n n n

MAP Recap of GSM Protocols and Interfaces GSM Call Flows and Short Message Subsystem Summary and Discussions 239

Call Call Flow Flow Discussions Discussions n n n n n n n n

Mobile to Land Call land to Mobile Call Mobile Initiated Call Clearing Inter BSS Handover Location Update Authentication and Ciphering EIR Identification IMSI Attach/Detach

240

Mobile Mobile to to Land Land Sequence Sequence MS

1

Channel Request DCCH Assign Signaling Link Established

BSS

MSC

VLR

HLR

EIR

PSTN

<SDCCH>

CR

2

Request For Service

3

Authentication

CC

Set Cipher Mode

4

Set Up

5

Equipment ID Request

<SDCCH> (Call Info)

241

Mobile Mobile to to Land Land Sequence Sequence MS

1

Channel Request DCCH Assign Signaling Link Established

BSS

MSC

VLR

HLR

EIR

PSTN

<SDCCH>

CR

2

Request For Service

3

Authentication

CC

Set Cipher Mode

4

Set Up

5

Equipment ID Request

<SDCCH> (Call Info)

242

Mobile Mobile to to Land Land Sequence Sequence MS

6 7

Complete Call <SDCCH>

MSC VLR (Call Data, TMSI)

HLR

EIR

PSTN

Call Processing <SDCCH>

Assignment Command Assignment Complete

8

BSS

(Circuit)

(Channel) <SDCCH>

IFAM ACM

Alerting MS Hears Ringtone From Land Phone

9

Answer (ANS) Connect

10

Ringtone Stops

Connect Acknowledge



BILLING STARTS

“Hello .. 243

Mobile Mobile to to Land Land Sequence Sequence MS

6 7

Complete Call

MSC VLR (Call Data,

<SDCCH>

Assignment Command

<SDCCH>

HLR

EIR

PSTN

TMSI)

Call Processing

Assignment Complete

8

BSS

(Circuit)

(Channel) <SDCCH>

IFAM ACM

Alerting MS Hears Ringtone From Land Phone

9

Answer (ANS) Connect

10

Ringtone Stops

Connect Acknowledge



BILLING STARTS

“Hello .. 244

Land Land to to Mobile Mobile Sequence Sequence MS

1 2 3

BSS

MSC

VLR

6

GMSC

IFAM Send Routing Info

(IMSI)

Routing Info. Ack

(MSRN)

(MSRN)

Page

Channel Request

(TMSI)

DCCH Assign



Signaling Link Established

<SDCCH> <SDCCH>

Page Response

(MSISDN)

(MSRN)

(MSRN)

Send Info For I/C Call Setup

Paging Request

PSTN

(MSISDN)

IFAM

4 5

HLR

(TMSI)

(TMSI)

(TMSI & Status)

(LAI & TMSI)

(Status)

Information Request And Exchange VLR-HLR *

245

Land Land to to Mobile Mobile Sequence Sequence MS

1 2 3

BSS

MSC

VLR

6

GMSC

IFAM Send Routing Info

(IMSI)

Routing Info. Ack

(MSRN)

(MSRN)

Page

Channel Request

(TMSI)

DCCH Assign



Signaling Link Established

Page Response

(MSISDN)

(MSRN)

(MSRN)

Send Info For I/C Call Setup

Paging Request

PSTN

(MSISDN)

IFAM

4 5

HLR

(TMSI)

(LAI & TMSI)

Information Request And Exchange VLR-HLR *

<SDCCH> <SDCCH> (TMSI)

(TMSI & Status)

(Status)

246

Land Land to to Mobile Mobile Sequence Sequence MS

BSS

MSC

*Authentication

7

Call Information

GMSC

PSTN

<SDCCH> (Call Info)

(Call Info)

<SDCCH> <SDCCH> (circuit)

Assignment Command (channel) Assignment Complete



Ringtone at MS



Alert

Ringtone at Land Phone

ACM

10

HLR

Complete Call Setup

8 9

VLR

Connect Subscriber Picks up

Connect Ack

Answer (ANS)





BILLING STARTS

Ringing Stops At Land Phone 247

Land Land to to Mobile Mobile Sequence Sequence MS

BSS

MSC

*Authentication

7

VLR

HLR

GMSC

PSTN



Complete Call Setup

8 9

<SDCCH >(Call Info)

(Call Info)

Assignment Command

<SDCCH > <SDCCH (circuit) > (channel)

Assignment Complete



Ringtone at MS



Call Information

Alert

Ringtone at Land Phone

ACM

10

Connect Subscriber Picks up

Connect Ack

Answer (ANS)





BILLING STARTS

Ringing Stops At Land Phone 248

Mobile Mobile Initiated Initiated Call Call Clearing Clearing MS

1

Disconnect

BSS

MSC

VLR

HLR

PSTN



PSTN Release Mobile Release

2

PSTN Release Complete Mobile Release Complete

3





Clear Command Channel Release



Clear Complete

4

Disc UA

5



RLSD Release Complete

249

Mobile Mobile Initiated Initiated Call Call Clearing Clearing MS

1

Disconnect

BSS

MSC

VLR

HLR

PSTN



PSTN Release Mobile Release

2

PSTN Release Complete Mobile Release Complete

3





Clear Command Channel Release



Clear Complete

4

Disc UA

5



RLSD Release Complete

250

Inter Inter -- BSS BSS Handover Handover Sequence Sequence 1

Periodic Measurement Reports

2 3

Hanover Required

MS BSS <SACCH>

BSS

MSC

(TMSI cct. code)

Handover Request (HO Ref. No.)

4 5 6 7 8

Information Interchange

9

Periodic Measurement Reports

Handover Req. Ack

Handover Command

Handover Complete

(HO Ref. No.)

HLR

PSTN

nBSS Assigns AirInterface Traffic Channel nBSS establishes level 2 signaling link on dedicated control channel and sends Timing Advance Cell ID Info. Etc.

Clear Command <SACCH> 251

Inter Inter -- BSS BSS Handover Handover Sequence Sequence 1

Periodic Measurement Reports

2 3

Hanover Required

MS BSS <SACCH>

BSS

MSC

(TMSI cct. code)

Handover Request (HO Ref. No.)

4 5 6 7 8

Information Interchange

9

Periodic Measurement Reports

Handover Req. Ack

Handover Command

Handover Complete

(HO Ref. No.)

HLR

PSTN

nBSS Assigns AirInterface Traffic Channel nBSS establishes level 2 signaling link on dedicated control channel and sends Timing Advance Cell ID Info. Etc.

Clear Command <SACCH> 252

Location Location Update Update Sequence Sequence 1

Channel Request

MS BSS

MSC

VLR

Location Update Request

3

Authentication

PSTN



DCCH Assign

2

HLR

Only sent to HLR If this is the first time the MS has Location Updated in this VLR.

<SDCCH>

(LAI & TMSI)

Ciphering

4

Forward New TMSI <SDCCH>

Location Update Accept

5

(TMSI)

TMSI Reallocate Complete

(TMSI) <SDCCH>

TMSI Ack

6

Clear Command Clear Complete

<SDCCH> <SDCCH> 253

Authentication Authentication and and Ciphering Ciphering MS

1

Pre-Send Triples to VLR

2

Authentication

BSS

Authentication Request

<SDCCH>

3

Authentication Response

<SDCCH> (SRES)

4 5

Start Ciphering

MSC

VLR

HLR

PSTN

EIR

(Rand) (Rand)

Cipher Mode Command

<SDCCH>

Cipher Mode Complete

<SDCCH>

254

Equipment Equipment Identification Identification MS

1

BSS

Equipment ID <SDCCH> Request

2

ID Response

3

Check IMEI

<SDCCH>

MSC

VLR

HLR

PSTN

EIR

Note: IMEI check may be deferred until after traffic channel has been established.

(IMEI)

Check IMEI Response 255

IMSI IMSI Attach/Detach Attach/Detach n

n n

n

When a mobile station is switched off (or when the SIM is removed by the user), the calls toward the corresponding subscriber can no longer be completed. Important resources are then consumed, and even not paid for, for nothing, whwnwver the mobile is paged. Upon a Mobile terminated call/SMS request, the establishment of the first part of the circuit (before HLR interrogation) cannot be avoided. However, the second portion, between the point where HLR interrogation is done and the visited MSC, can be avoided using the IMSI Attach/Detach mechanism. 256

IMSI IMSI Attach Attach Status Status n

n

The subscriber's record in the MSC/VLR contains a binary information called Attach Status indicating whether it is useful or not to try to complete a call toward this subscriber. The mobile station triggers an IMSI Detach when it goes inactive, and either a location updating procedure (if in a new' location area) or an IMSI Attach procedure when it comes back on (in the same location area).

257

IMSI IMSI Attach/Detach Attach/Detach n

n n

n

When a mobile station is switched off (or when the SIM is removed by the user), the calls toward the corresponding subscriber can no longer be completed. Important resources are then consumed, and even not paid for, for nothing, whwnwver the mobile is paged. Upon a Mobile terminated call/SMS request, the establishment of the first part of the circuit (before HLR interrogation) cannot be avoided. However, the second portion, between the point where HLR interrogation is done and the visited MSC, can be avoided using the IMSI Attach/Detach mechanism. 258

IMSI IMSI Attach Attach Status Status n

n

The subscriber's record in the MSC/VLR contains a binary information called Attach Status indicating whether it is useful or not to try to complete a call toward this subscriber. The mobile station triggers an IMSI Detach when it goes inactive, and either a location updating procedure (if in a new' location area) or an IMSI Attach procedure when it comes back on (in the same location area).

259

Call Call Rejection Rejection by by MSC/VLR MSC/VLR n

n

The basic scenario of a mobile terminating call set-up attempt requires an interrogation of the visited MSC/VLR by the HLR before the latter provides the information necessary for the continuation of the routing. This phase allows the visited MSC/VLR to reject the call on the basis of the attach status before the costly set up of the traffic circuit. – If it does so, call forwarding if applied can potentially be controlled by the HLR. – Another possibility is that the visited MSC/VLR accepts the call, and applies the call forwarding itself if required. 260

IMSI IMSI Detach Detach n

n

n

The IMSI Detach procedure consists of a single message, the RIL-3 MM IMSI Detach message, from the mobile station to the visited MSC/VLR. This message is not acknowledged, simply because it has been considered that the mobile station is typically switched off, or more generally not in a position to receive an answer from the network. The mobile station keeps no track of having asked for a detach (for instance by storage in the SIM): the state of the attach/detach information in the network is not monitored by the mobile station. 261

IMSI IMSI Attach Attach n

The MS starts an IMSI Attach procedure, that is to say (except for a negligible detail) a location updating procedure. – if attach is indicated as supported in the cell the it has chosen at switch-on (or SIM insertion) and – if the it knows the subscriber is already registered in the same location area.

262

Similarities Similarities n

n

Periodic location updating and the IMSI Attach procedure, over the air, are almost identical to location update procedures. Their main differences are mostly the events that trigger them.. These IMSI Attach/Detach procedures are very close functionally to the call forwarding supplementary services in the case where the mobile station is not deregistered.

Location Update

Call Forwarding IMSI Attach/Detach 263

Short Short Message Message Service Service (Rev.) (Rev.) n

n

n

Unlike circuit switch communication such as speech and video, short message services do not require the end-to-end establishment of a traffic path. A short message communication is limited to one message or in other words the transmission of one message is a communication all by itself. SMS service is asymmetric, so the Mobile Originating Short Message transmission is considered as a different service from the Mobile Terminating Short Message transmission.

264

Short Short Message Message Service Service Center Center n

The transmission of a message is always relayed by a Short Message Service Center (SM-SC), considered to be outside the GSM specifications. – Therefore, the transfer of a short message always takes place between a mobile station and some SM-SC from the point of view of the GSM infrastructure. – However, for the user, the message has also an ultimate destination or origin, identified by some field in the message, but relevant only for the user and the SM -SC not for the GSM infrastructure.

n

The SM-SC – – – –

Sorts and store the messages Delivery the messages to the MS Provides Billing data And user data administration 265

SM -Gateway SM-Gateway n

The point-to-point short message services defined in GSM enable the transfer of short messages between the mobile station and a short message service center which is in contact with GSM networks through specific MSCs called SMS-GMSC (for Mobile Terminating Short Messages) or SMS-IWMSC (for Mobile Originating Short Messages), referred hereafter, both as SMS-gateway

266

SMS SMS Architecture Architecture MAP-D (location of MS)

MSC/VLR

MAP-H (forward messages)

SM-RP SM-CP

HLR MAP-C(routing) SMS-GW

SM_TP

SM-SC 267

SMS SMS Protocols Protocols The protocols involved in SMS management include n

n

n

the mobile station to SM-SC protocol, called Short Message Transport Protocol (SM-TP)), enables the transport of short messages, whether from or to the mobile station. the protocol between the SMS-gateway and HLR enables the SMS-gateway to interrogate the HLR in search of the address of the subscriber when reachable; it is part of the MAP/C protocol the protocol between MSC and HLR. as well as the protocol between HLR and SMS-gateway. enable the alerting of the SMSC when a mobile station has missed a message while it was out of reach but has subsequently become reachable. This function must also be supported on the interface between the SMS-gateway and the SM-SC, but the protocols on this interface are not defined in the specifications. 268

SM -MO/PP SM-MO/PP n

n

n

n

Allows the mobile to send short message to other mobile or other devices(devices that are located within the PSTN,PSDN, LAN, WAN) via the signaling channel. This allows the mobile to send a message while in a call. The MS must send the content of the message along with the address of the receiver and the address of the SM_SC. The SM-TP protocol will be used to send the messages to the SMSC and an acknowledgment is send back to the MS that the SM_SC has received the message. This service will impact the network planning, depending on number of subscribers using the service

269

SM -MT/PP SM-MT/PP n

n

n

Allows the mobile subscriber to receive short message via the signaling channel from the SM-SC. The short message will be delivered from the SM-SC to the MSC via the SM-TP protocol indicating the ID of the sender and time stamp of the message received. In order for the message to reach its destination, the HLR of the subscriber must be interrogated . – is the MS subscribed for this service? – is there any call barring active etc.)by the SMGW(finding the HLR based on the MSISDN) .

270

SM -MT/PP (cont.) SM-MT/PP (cont.) n

n

Once the MSC/VLR of the subscriber has been identified and it is reachable the message is forwarded to the MSC. The MSC/VLR after successful determination of the location of the MS will attempt paging the MS in the location area. If the subscriber is not able to receive the short message (either SIM does not have enough memory or the paging of the subscriber is unsuccessful or etc.) the message will be kept in the SM-SC for later delivery, the HLR /VLR will take a note of this for when the subscriber is available again.

271

Chapter Chapter 2: 2: Review Review and and Discussions Discussions

Signaling Network Protocols and Interfaces Call Flows & SMS

272

Chapter Chapter 3: 3: n

Review of Probability Theory – Review of Basic Probability Concepts – Useful Distributions – Basics of Statistical Methods

n

Basic Traffic Model – – – –

n

Arrival Process, Erlang and Blocking Definition Queuing Strategy and Markov Chain Formulation Erlang B, C and Poisson Models and Calculations

Contention Based Multiple Access Protocols – P-ALOHA and S-ALOHA – CSMA and ISMA

n n

Subscriber Forecast and Demographic Analysis Summary and Discussions 273

Review Review of of Probability Probability Theory Theory Distribution Function

0.286799 0.369247

0.7

1

0.441248 0.6

0.501162

1.4

0.580919 0.600279

0.4

2

0.558425 0.525436

0.1

3.6

0.356218

3.8

0.312501

4

0.270671

4.2

0.231526

4.4

0.195628

4

6

8

8.

9

2

7.

9.

6

7.

6

0.44486 0.400768

6.

3.4

0.486979 0

4

3.2

8

3

5.

2.8

0.584103

2

2.6

0.600682

0.2

4.

2.4

0.606531 0.3

6

2.2

4.

1.8

0.547893

3

1.6

0.5

3.

1.2

4

0.8

8

Correlation

0.19604

0.6

2.

n

0.4

1.5

P o2i s s o n D i s t r i b u t i o n

2

–

Mean Variance

0 0.099501

1.

–

0 0.2

6

n

Independence Expected Value

1.

n

0

–

0.

–

Probability Density Function Probability Mass Function Commutative Distribution Function

Function

–

Probability Density

n

Number of Users

274

Quick Quick Question Question n

Find the end-to-end service availability from point A to D, assuming the given set of availability of links and network elements. β A

n

Answer:

α

γ

B

β

PA-B = α.[1− α.[1−(1− (1−β)2].γ 275

Exponential Exponential Distribution Distribution n

n

n

n

Let τ be a random variable, denoting the duration of a certain event, e.g. call duration. Τ has a Exponential distribution if λe −λτ if τ ≥ 0 f Τ ( τ) =  otherwise  0 Where λ is some positive constant The mean time duration time is 1 E (T ) = λ The variance of time duration is 1 σ = 2 λ 2 Τ

276

Properties Properties of of Exponential Exponential Distribution Distribution n

An exponential random process is Memoryless

Pr( X n > a + b | X n − 1 = a ) = Pr( X n > a + b ) n

The minimum of a group of N exponential random variables with parameters µ i is an exponential random variable with parameter N

µ = ∑ µi i =1

277

Poisson Poisson Distribution Distribution n

n

Let N be a random variable, denoting the number of occurrences of a certain event, e.g. call arrivals, during a time interval of duration T. N has a Poisson distribution if n λ ( T ) − λT P( N = n ) = e n!

n

Where λ is some positive constant The mean number of events (arrivals) during time interval of T is

E( N = λT (arrivals) during The variance of the number of) events time interval of T is 2 = λT σ σ NN = λT

278

Why Why Poisson? Poisson? n

n

A Poisson process is generally considered to be a good model for the aggregate traffic of a large number of similar and independent users. Theorem: Suppose that we merge n independent and identically distributed packet arrival processes. – Each process has arrival rate λ /n, so that the aggregate process has arrival rate λ . – The interarrival times τ between packets of the same process have a given distribution F(s ) = P{ τ < s} and are independent [ F(s ) need not be an exponential distribution]. – Then under relatively mild conditions on F, e.g. F(0)=0 and dF(0)/ds > 0, the aggregate arrival process can be approximated well by a Poisson process with rate λ when n is large. 279

Properties Properties of of Poisson Poisson Arrivals Arrivals n

The number of arrivals n in any time interval of duration T is given by a Poisson distribution

( λT ) n − λ T P( N = n ) = e n! n

Where λ is some positive constant The number of arrivals in disjoint time intervals are independent.

280

Properties Properties of of Poisson Poisson Arrivals Arrivals n

The inter-arrival time or the time between successive arrivals τ is an exponentially distributed random variable with parameter λ .

λe − λτ if τ ≥ 0 f Τ (τ) =  otherwise  0 n

Inter-arrival times are independent random variables.

n

Question: What is the cdf of this process.

281

Properties Properties of of Poisson Poisson Arrivals Arrivals Let X be a Poisson arrival process, n The probability of a new arrival within the next t unit of time is essentially proportional to h with λ being the constant of proportionality

Pr(1 new arrival )

= λt + o( t ) ≈ λt

Noforarrival soPr( that small)t

= 1− λt + o(t ) ≈ 1− λt

so that for small t

Similarly

n

n

So Pr( 2 or more arrivals during t) is O(t) or essentially zero. Arrivals during disjoint intervals are independent.

282

Merging Merging Poisson Poisson Arrivals Arrivals Poisson Arrival with Rate λ1

Independent

Poisson Arrival with Rate λ2

Which Distribution? What Rate? n

Theorem & Proof !! 283

Splitting Splitting Poisson Poisson Arrivals Arrivals S

Poisson Arrival with Rate λ

Poisson Arrival with Rate λ1

S1 Which Distributions? S2 What Rate?

n

If a Poisson process is split into two other processes by independently assigning each arrival to the first (second) of these processes with probability p (1 - p, respectively). The two arrival processes thus obtained are Poisson. 284

Alternative Alternative Models Models n

Due to – Variations in of service statistics – User’s preferences and usage patterns – and emerging new services, e.g. circuit and packet switch data

The classical Poisson models may not be appropriate in certain applications and markets. n Therefore new empirical or theoretical models have to be developed. n These models need to be confirmed and tested against measure statistics.

285

Statistical Statistical Methods Methods n

n

n n n

One of the objectives of statistical methods is to test the validity of a model. The first step is to obtain a random sample, e.g. of size n, for X. Generate the sample cdf of X, FS(x) Consider the cdf of candidate distribution, FC(x) Compute the maximum difference between the two functions D = sup | F ( x ) − F ( x ) | n

x

C

S

286

K -S Test K-S Test n

Kolmogorov-Smirnov Test Says: – The hypothesis that a given sample comes from a candidate distribution can be accepted or rejected with a confidence level based on the value of cdf of – Y=sqrt(n) * D n

lim Pr( n →∞

n D n ≤ y) ≡ H ( y) ∞

= 1 − 2∑ (−1) e i =1

i −1 − 2i 2 y 2 287

Example Example n n n

A random sample of call holding times have been measured. The sample size is 400. Sample cdf is generated An exponential distribution is considered as candidate. – – –

n

The maximum difference between the candidate and sample cdf is computed to be 0.05. Y=sqrt(400)*0.05=1.0 H(1)=0.73

Thus the probability that the sample size indeed come from the candidate exponential distribution, or the confidence level, is 0.73. 288

Chapter Chapter 3: 3: n

Review of Probability Theory – Review of Basic Probability Concepts – Useful Distributions – Basics of Statistical Methods

n

Basic Traffic Model – – – –

n

Arrival Process, Erlang and Blocking Definition Queuing Strategy and Markov Chain Formulation Erlang B, C and Poisson Models and Calculations

Contention Based Multiple Access Protocols – P-ALOHA and S-ALOHA – CSMA and ISMA

n n

Subscriber Forecast and Demographic Analysis Summary and Discussions 289

Traffic Traffic Model Model n

In traffic engineering problems typically the following assumptions are made – –

Call arrivals form a Poisson process with average call arrival rate of λ The duration of each call (often called the holding time) is an exponentially distributed random variable with parameter µ , which is independent from other calls’ duration and the system load. »

This implies that the average call duration is …….. 290

Service Service Time Time Statistics Statistics n

n

n n

Our assumption regarding the service process is that the Customer service times have an exponential distribution with parameter µ , The parameter µ is called the service rate and represents the rate (in customers served per unit time) at which the server operates when busy. Furthermore. the service times sn are mutually independent and also independent of all interarrival times. An important fact regarding the exponential distribution is its memoryless character. – This means that the additional time needed to complete a customer's service in progress is independent of when the service started. – Similarly, the time up to the next arrival is independent of when the previous arrival occurred, 291

Traffic Traffic Model Model (cont.) (cont.) n

The amount of traffic load is proportional to – –

n

n

average arrival rate λ average call holding time or call duration 1/µ µ

Therefore the product of call arrival rate and call duration is a dimensionless quantity A=λ/µ λ/µ denoted as “Erlangs” measuring the offered load. For Example: –

If the average call arrival rate is 10 calls per minute and an average call last for 2 minutes, then the offered load is 10 x 2=20 A or 20 Erlangs. 292

Some Some Parameters Parameters of of Interest Interest n

We are typically interested in estimating quantities such as. – The average number of customers in the system (i.e. the “typical" number of customers either waiting in queue or undergoing service) – The average delay per customer (i.e. the “typical" time a customer spends waiting in queue plus the service time).

n

These quantities will be estimated in terms of known information such as: – The customer arrival rate (i.e.. the “typical" number of customers entering the system per unit time) – The customer service rate (i.e., the “typical” number of customers the system serves per unit time when it is constantly busy) 293

Number of Arrivals α (t) Number of Departures β (t)

Arrivals Arrivals & & Departures Departures

N(t) α(t) β (t)

time 294

Defining Defining Parameters Parameters n n n

N(t)=Number of customers in the system at time t α(t)= Number of customers arrived in the interval [0 , t] Ti = Time spent in the system by the ith arriving customer

Steady State Number of Customers in the System

N = lim N t

where

Steady State Arrival Rate

λ = lim λt

where

Steady State Time Average Customer Delay

t →∞

t →∞

T = lim Tt t →∞

1 t N t = ∫ N (τ )dτ t 0 α (t ) λt = t α (t )

where

Tt =

∑T i =0

i

α (t ) 295

Little’s Little’s Theorem Theorem Little's Theorem establishes the following relation N=λ λT λ N=λ λT between the basic quantities, n

– N = Average number of customers in the system – T = Average customer time in the system n

T

Application of the same idea to a queuing system results in NQ=λ λW – NQ = Average number of customers waiting in queue – W= Average customer waiting time in queue

n

However, N, T, NQ, and W cannot be specified further unless we know something more about the statistics of the system. 296

Application Application of of Little’s Little’s Theorem Theorem n

Given system statistics, we will be able to derive the steady-state probabilities

n n

π i= Probability of i customers in the system, i = 0.1,…. From these probabilities, we can get ∞

N = ∑ iπi i =0

n

and using Little's Theorem,

n

Similar formulas exist for NQ and W.

N T= λ

297

Blocking Blocking Concepts Concepts The number of active calls is a Poisson random variable of mean λ/µ. 0

0

0.2

0.099501

0.4

0.19604

0.6

0.286799

λ/µ

0.369247

0.7

0.441248 0.6

0.501162

1.4

2

0.600682 0.584103

0.2

2.6

0.525436

0.1

3

3.6

0.356218

3.8

0.312501

4

0.270671

4.2

0.231526

4.4

0.195628

4 8.

6

8 7.

9.

2 7.

9

6

4 5.

6.

8 4.

6

2 4.

6

0.400768

3.

6

0.44486 0.

3.4

0

3.2

0.486979 0

3

2.8

0.558425

4

2.4

0.606531 0.3

2.

2.2

Blocking Probability

0.600279

0.4

8

1.8

0.580919

1.

1.6

0.547893 0.5

2

Probability Density Function

1

1.2

P o2i s s o n D i s t r i b u t i o n

1.

0.8

1.5

Number of Users

298

Classical Classical M/D/m/n M/D/m/n Notation Notation

M/D/m/n

n

n n

n

the number of users in the system, including users in the queue. the number of servers. the probability distribution of the service times (e.g., M, G, and D stand for exponential, general, and deterministic distributions, respectively). the nature of the arrival process {e.g., M: for memoryless, G for general distribution, D for deterministic interarrival time. 299

Chapter Chapter 3: 3: n

Review of Probability Theory – Review of Basic Probability Concepts – Useful Distributions – Basics of Statistical Methods

n

Basic Traffic Model – – – –

n

Arrival Process, Erlang and Blocking Definition Queuing Strategy and Markov Chain Formulation Erlang B, C and Poisson Models and Calculations

Contention Based Multiple Access Protocols – P-ALOHA and S-ALOHA – CSMA and ISMA

n n

Subscriber Forecast and Demographic Analysis Summary and Discussions 300

Queuing Queuing Strategy Strategy n

We assume – – –

n

All circuits or servers are the same No special priority is considered and if a circuit is available it will be allocated to a requested call

There are three common strategies for handling arriving requests: – – –

Blocked Calls Cleared (Erlang B Model) Blocked Calls Delays (Erlang C Model) Block Calls Held (Poisson Model)

301

Markov Markov Chain Chain Formulation Formulation n

n

An important consequence of the memoryless property is that it allows the use of the theory of Markov chains. Indeed. this property, together with our earlier independence assumptions on interarrival and service times, imply that – once we know the number N(t) of customers in the system at time t, the times at which customers will arrive or complete service in the future are independent of the arrival times of the customers presently in the system and of how much service the customer currently in service (if any) has already received. – This means that the future numbers of customers depend on past numbers only through the present number: that is, {N(t) > 0} is a continuous-time Markov chain, 302

System System State State Transition Transition n

n

n

n

Under these assumptions the state of the system forms a Markov Chain. In such a formulation, being in State i implies that there are i users in the system. The probability of transition from one state to another as result of a new call arrival or termination, depends on the queuing strategy of the system Flow Conservation Law is

πi,i+1 π i,i i

i+1

π i+1,i+1

πi+1,i

Pi × π i ,i +1 = Pi +1 × π i +1,i 303

Erlang Erlang BB State State Transition Transition λ

λp0 = µp1 λp1 = 2 µp2 λp2 = 3µp3

0

λ 1

µ

λ 2

2µ

λ 3

3µ

λ

…...

λ N-1

4µ (Ν− (Ν−1)µ

N

Νµ

λp N −1 = Nµp N 1 N λ p0 = N ! µ p N ⇒ p N = λ / µ ) p0 ( N! N

N

304

Erlang Erlang B, B, Blocking Blocking Probability Probability n

The fraction of time that all N servers are busy or the blocking probability is the probability that an arbitrary arrival find the system in the Nth state.

N  A 11  λ  N  pπNN =  λ / µπ 0 p0 N! P ( A , N ) = N!! µ   B N Ai ∑ pπ01++ pπ12++ pπ23++......++pπN N==11 i =1 i!

(

n

N

)

This is a traditional M/M/N/N system in queuing theory. 305

Offered Offered vs. vs. Carried Carried vs. vs. Traffic Traffic n

The offered load is split into – –

Offered Traffic

Carried Calls C(A,N), and Blocked calls B(A,N) or overflow traffic Overflow Traffic

can be defined ratio) between carried A Utilization = A * PB(A,N) +A * ( 1 -as PBthe (A,N) Carried

n

load and the number of channels or circuits. U(A,N)=C(A,N)/N

Traffic

306

Peakedness Peakedness n

n

Peakedness of a random process is measured as ratio between its variance and average squared. Peakedness of random traffic is an important factor to be considered in design of trunking systems.

m

σ

Variance Peakedness = (Average)2

σ2 = 2 m

307

Peakedness Peakedness n n

A Poisson arrival has a peakedness of ……… How about carried traffic or blocked (or Arrived Traffic overflow) traffic?

σC ZC = 2 < 1 MC 2

σB ZB = 2 > 1 MB 2

Overflow Traffic

Carried Traffic 308

Utilization Utilization vs. vs. N N n n

Using Erlang B Table: Generate a curve for Utilization as a function of Number of channels, assuming %1 blocking probability.

309

Utilization Utilization vs. vs. Blocking Blocking n n

Using Erlang B Table: Generate a curve for Utilization as a function of blocking probability, assuming 50 channels.

310

Erlang Erlang vs. vs. N N n n

Using Erlang B Table: Generate a curve for Supported erlangs as a function of number of channels, assuming %2 blocking.

311

Erlang Erlang vs. vs. GoS GoS n n

Using Erlang B Table: Generate a curve for Supported erlangs as a function of Blocking, assuming 50 channels.

312

Exercise Exercise n

60 channels are to be allocated to a BTS are there are two choices: (Both configurations have the same coverage) – Use an omnidirectional cell and assign all 60 channels to it. – Use a sectorize cell and allocate 20 channels to each sector.

n

Which choice will carry higher traffic load?

60 n n n

20 20 20

What is the impact of sectorization on trunking efficiency? What is the impact of sectorization on cell capacity? What is the impact of sectorization on system capacity? 313

Blocked Blocked Calls Calls Delayed Delayed Model Model n

n n

This model assumes N servers (or channels) and an infinite queue size. It is usually considered as an M/M/m system. The corresponding state transition diagram is shown.

λ 0

λ 1

µ

λ 2

2µ

λ

…... 3µ

λ N-1

(Ν− (Ν−1)µ

λ N

Νµ

λ N+1

Νµ

λ N+2

Νµ

…... Νµ 314

Erlang Erlang C C n

n

The pdf of number of users in the system can be calculated using the diagram and similar procedures to what we used for Erlang B k model.  A if k ≤ N  P0 The result is

where

k! Pk =  k N −k A N P0  N!

1 P 0 = N −1 k N A A N + ∑ N! N − A k =0 k!

if k > N

&

A
Blocking -C Blocking in in Erlang Erlang-C n

Probability of a call waiting in the queue for a time T exceeding t is given by: N P (T > t ) = PB (A , N )e −( N −A )µt N − A (1 − PB (A , N ))

n

Therefore the probability of “having to wait” or PQ is ∞ Pr( Queueing ) = ∑ Pk = P (T > 0) k=N

1 = N−A 1+ APB ( A, N − 1) n

A≤N

The following equation is usually referred to as Erlang C N Formula p A N

PQ =

0

N! N − A

316

Notice: Notice: n n

n

n

Note that PQ (A,N)|Erlang C > PB(A,N) | Erlang B It is not correct to directly compare these two probabilities, because they apply to different models and they have totally different meanings. Erlang C model has no blocking, it merely has queuing. Keeping this in mind it is sometimes useful to compare blocking probability of one model with the those obtained using other models. 317

Users Users in in Queue Queue or or System System n

When A < N The average number of calls waiting is E(N) =

PQ (A, N) A

A
N−A

and the mean waiting time of a call is E ( W) = Pr( T > 0) n n

1 µ( N − A )

A
For A > N both E(N) and E(W) tend to infinity. The average user time in the system and average number of users in the system are: T = 1 / µ + W

A Nc = A + N−A

318

Some Some Observations Observations n

The average waiting time depends on – –

n

the average holding time and the amount of load in Erlangs

These equations – –

hold only for systems which have a non-biased service discipline such as LIFO or FIFO do not hold for systems which have a biased service discipline such as shortest service time first. The distribution of the waiting time, however, does depend on the choice of service discipline.

319

Poisson Poisson Model: Model: Blocked Blocked Calls Calls Held Held n

In Poisson Model blocked arrivals –

– –

n

wait for a random amount of time, the distribution of which is assumed to be the same as holding time distribution. clears the system once the Waiting Timer expires arrivals, not served immediately are considered blocked

The Blocking Probability for system based on Poisson Model using similar assumptions about the arrival process is N −1

i A PP ( Blocking ) = 1 − e − A ∑ i =1 i!

320

Poisson Poisson Model Model (cont.) (cont.) Poisson model can be considered as classical M / M / ∞ model. n Poisson Model is an intermediate and to some extent more realistic than Erlang B and C models. (Why?) n

–

–

In many cases where fast redialing is very common this model reflects the traffic dynamics more closely. However, in systems where the blocked calls can be rerouted to other servers, Erlang B model seems to be more appropriate. 321

Chapter Chapter 3: 3: n

Review of Probability Theory – Review of Basic Probability Concepts – Useful Distributions – Basics of Statistical Methods

n

Basic Traffic Model – – – –

n

Arrival Process, Erlang and Blocking Definition Queuing Strategy and Markov Chain Formulation Erlang B, C and Poisson Models and Calculations

Contention Based Multiple Access Protocols – P-ALOHA and S-ALOHA – CSMA and ISMA

n n

Subscriber Forecast and Demographic Analysis Summary and Discussions 322

Contention Contention Based Based (Random) (Random) MA MA n

n

n

With the contention multiple access protocols there is no scheduling of transmissions. This means that a user getting ready to transmit does not have exact knowledge of when it can transmit without interfering with the transmissions of other users. This possible transmission failure makes the occurrence of a successful transmission a more or less random process. The random access protocol should resolve the contention that occurs when several users transmit simultaneously. Collision

Successful TX

Wasted Channel

Channel Idle

323

Throughput Throughput n

In a random access channel time can be divided into – Idle Time, No packet is transmitted – Colliding Time, more than one packet transmitted – Successful Time, One packet is successfully transmitted

n

n

The fraction of successful time to total time can be thought of as the throughput of the system. It is the fraction of messages that are send successfully sent/received to how many could be sent/received, should we had a perfect scheduling/controller. Collision

Successful TX

Wasted Channel

Channel Idle

324

Contention Contention Based Based MA MA n

n

We can subdivide the contention multiple access protocols into two groups, Repeated random access protocols – With every transmission there is a possibility of contention and

n

Random access protocols with reservation. – only in its first transmission does a user not know how to avoid collisions with other users. However, once a user has successfully completed its first transmission (once the user has access to the channel), future transmissions of that user will be scheduled in an orderly fashion so that no contention can occur. 325

Repeated Repeated Random Random Access Access Protocols Protocols n

n

n

At the start of each transmission by a user, the user does not know if other users will also begin transmitting. Therefore, contention will occur if two or more users start transmitting at more or less the same time. If the users are also not able to detect an ongoing transmission, then contention will also occur if a new user starts a transmission while another user is already busy. If a user can sense an ongoing transmission, it can defer its own transmission until the channel is free. Contention can then only occur if two or more users start transmitting at the same time. 326

Repeated Repeated Random Random Access Access Protocols Protocols n

In this section some of the following repeated random access protocols are described: – – – – –

pure (p)-ALOHA, slotted (s)-ALOHA, carrier sense multiple access (CSMA), inhibit sense multiple access (ISMA), and stack algorithm. 327

pp-ALOHA -ALOHA n

n

The Aloha network was developed around 1970 to provide radio communication between the central computer and various data terminals at the campuses of the university of Hawaii Immediately after a user has generated a packet it will transmit this packet on the uplink channel. –

If no other users transmit, the base station will receive a correct transmission and send an acknowledgment packet on the down link channel. On reception of the acknowledgment, the user knows its transmission has been successful.

328

pp-ALOHA -ALOHA – If two or more users transmit simultaneously, a collision will occur. The base station recognizes this occurrence because it receives a garbled transmission and does not transmit an acknowledgment. When a user does not receive an acknowledgment, it assumes its transmission has collided so it will have to retransmit. – Simply retransmitting after a fixed time interval will not do, because two users that transmitted at the same time will find out about the collision at about the same time and therefore retransmit at the same time, thus creating another collision. – To avoid this deadlock situation, a user experiencing a collision will wait a random amount of time before retransmitting. 329

pp-ALOHA -ALOHA (cont.) (cont.) n

n

As figure shows that user 1 starts transmission at t=t 0. Assume a transmission takes T seconds, so the transmission of user 1 ends at t=t0+T. As can be seen from the figure, the transmission of a user starting anywhere within the time period between t0-T to t0+T will collide with the transmission of user 1 (indicated as the shaded area in the Figure). As a result the transmission of user 1 there is a vulnerable period of 2T (2 times the duration of a transmission). Note that we assumed the propagation delay to be negligible compared to the time needed to transmit a packet. Other Users User 1 t0-T

t0

t0+T

t0+2T 330

Pure Pure Aloha Aloha Throughput Throughput Assuming Poisson Arrivals with an arrival rate of G arrivals/slot the throughput rate S for pALOHA is given by: Pure ALOHA 0.2 0.18 0.16 0.14 0.12 S

n

0.1 0.08 0.06 0.04 0.02 0 0

2

4

6

8

G

331

Slotted Slotted Aloha Aloha n

n

n

One way to improve the performance of p-ALOHA protocol is to try and make the vulnerable period smaller. This can be done by dividing the transmission time axis into time slots and requiring that a user is only permitted to start its transmission at the start of a time slot. The transmission of this packet is delayed until time t=T (indicated by an arrow followed by the packet) and only those users that generated a packet between time 0 and T will also transmit at time T and collide with the transmission of user 1. Users that generate a packet after time t=T will not start transmission until time i=2T and will therefore not collide with the transmission of user 1. The vulnerable period of a transmission is now only T so it is halved compared to p-ALOHA. This doubles the maximum channel throughput to 36%. The resulting protocol is called the slotted (s-)ALOHA protocol. Other Users User 1 0

T

2T

3T

332

Slotted Slotted Aloha Aloha Assuming Poisson Arrivals with an arrival rate of G arrivals/slot the throughput rate S is given by: Slotted ALOHA 0.4 0.35

S

n

S = Ge

0.3 0.25 0.2 0.15 0.1 0.05 0 0

1

2

3

4

−G

5

6

G

333

Equilibrium Equilibrium Point Point

n n

In equilibrium the arrival rate, λ , to the system should be the same as the departure rate, Ge-G. This relationship is illustrated in Figure. We see that the maximum possible departure rate (according to the argument above) occurs at G = 1 and is l/e=0.368. Slotted ALOHA 0.4 0.35

S

n

Departure Rate S

0.3 0.25 0.2 0.15

Arrival Rate λ

0.1 0.05 0 0

1

2

3

4

5

6

G

334

Operating Operating Point Point n

n

n

n

In G > 1 region the system is unstable, because the accumulation of retransmissions saturates the channel resulting in 0 throughput. The G=1 point is the unset of instability and therefore is not a good operating point. Usually the 0.3 < G < 0.5 region is considered to be feasible. Obviously the system behavior highly depends on the retransmission strategy defined in the protocol. For example –

Random Attempts Max. No. Attempts

–

Access Classes

–

335

S

Aloha Aloha vs. vs. Slotted Slotted Aloha Aloha 0 0.2 0.4 0.6 0.4 0.8 0.35 1 0.3 1.5 0.25 2 0.2 2.5 3 0.15 3.5 0.1 4 0.05 4.5 0 5 6 7

0 0 0.163746 ALOHA 0.134064vs. Slotted ALOHA 0.268128 0.179732 0.329287 0.180717 0.359463 0.161517 0.367879 0.135335 s-ALOHA 0.334695 0.074681 −G S = Ge 0.270671 0.036631 0.205212 0.016845 0.149361 0.007436 p-ALOHA 0.105691 0.003192 0.073263 S =0.001342 Ge −2 G 0.04999 0.000555 0.03369 0.000227 0 2 4 6 0.014873 3.69E-05 0.006383 5.82E-06 G

8

336

SS-ALOHA -ALOHA vs. vs. TDM TDM n

n

n

The basic idea of s-ALOHA algorithm is that each unbacklogged node simply transmits a newly arriving packet in the first slot after the packet arrival. Thus risking occasional collisions but achieving very' small delay if collisions are rare. This approach should be contrasted with TDM in which, with m nodes, an arriving packet would have to wait for an average of m/2 slots for its turn to transmit. Thus, slotted Aloha transmits packets almost immediately with occasional collisions. whereas TDM avoids collisions at the expense of large delays.

337

Example Example 1: 1: Low Low Traffic, Traffic, No No Mobility Mobility n n n

Suppose the base station has only 7 traffic channel GoS is %2 Also Assume – Very low degree of mobility, No location update, No SMS traffic

n n

The average call holding time is 2 minutes Then we have: – N=7 (why?) and B=0.02 – 1/µ µ =2min – Then

From Erlang B table: A= 2.93

arrival rate is λ =2.93/2=1.46 calls/minute 146 . × 4.6m sec 60 sec G = 0.0001 arrivals / slot << 0.2 G = 1.46 arrivals / min =

So There is no problem at all!! 338

Ex. Ex. 2: 2: Low Low Traffic Traffic & & High High Mobility Mobility n n n

Suppose the base station has 47 traffic channel GoS is %2 Also Assume – Very high degree of mobility, high rate of registration and location update. So for every user originating call there are 100 users performing location updates and registration.

n n

The average call holding time is 2 minutes Then we have: – N = 47

and

B=0.02

From Erlang B table: A= 37.4

– 1/µ µ =2min arrival rate is λ =37.4/2=18.7 calls/minute – Then G = 18.7 × (100 + 1) arrivals / min = 189 . × 103 × 4.6m sec/ slot G= 60 sec G = 0145 . arrivals / slot < 0.2 So There is still no problem.

339

Ex. Ex. 3: 3: High High Traffic Traffic & & High High Mobility Mobility n n n

Suppose the base station has 119 Traffic channel GoS is %2 Also Assume – Very high degree of mobility, high rate of registration and location update. So for every user originating call there are 100 users performing location updates and registration.

n n

The average call holding time is 2 minutes Then we have: – N = 119 and

B=0.02

From Erlang B table: A= 106.4

– 1/µ µ =2min arrival rate is λ =106.4/2=53.2 calls/minute – Then G = 53.2 × (100 + 1) arrivals / min = 5.37 × 103 × 4.6m sec/ slot G= 60 sec G = 0.411 arrivals / slot > 0.2

So the system is almost unstable and there is a problem.

340

Carrier Carrier Sense Sense MA MA n

CSMA is a class of protocols which we can divide into two subclasses: – the nonpersistent CSMA protocols and – the p-persistent CSMA protocols.

n

In the nonpersistent CSMA protocols, a user that has generated a packet first "listens" to (senses) the channel for transmissions of other users. – If it senses the channel idle, it will transmit; – otherwise the user will wait a random time and then try again.

341

Carrier Carrier Sense Sense MA MA (cont.) (cont.) n

n

Figure shows a transmission from user 1 that starts at t0. With a propagation delay between user I and user 2 of tp , user 2 will sense the channel idle between t0 and t0+tp Therefore, if user 2 generates a packet within this time a colliding transmission will result. A user is informed of a collision by the absence of an acknowledgment packet from the receiving station. Upon detecting the collision, the packet is rescheduled for transmission a random time later. User 1 User 2 t0

t0+tp

time342

11-Persistent -Persistent CSMA CSMA n

n

n

A special case of the p-persistent CSMA protocols is the 1-persistent CSMA protocol. The protocol is the same as the nonpersistent CSMA protocol except when a user senses the channel busy. In this case the transmission is not rescheduled a random time later but instead the user keeps sensing the channel until it becomes idle and then immediately transmits its packet. As a result of this, all users that become ready during a busy channel will transmit as soon as the channel becomes idle, which leads to a high probability of a collision at the end of a successful transmission. 343

11-Persistent -Persistent CSMA CSMA n

n

n

To avoid the collision of packets accumulated while the channel was busy, the start of the transmission times of the accumulated packets can be randomized. This can be done by letting all users that generate a packet during a busy channel transmit as soon as the channel becomes idle with a probability p. With a probability 1-p they will defer their transmission for τ seconds (with τ being the maximum propagation delay between any two users in the system). After the τ seconds the deferred terminal will sense the channel again and apply the same algorithm as before. 344

CSMA -CD CSMA-CD n

With the nonpersistent and p-persistent CSMA protocols, a user will not learn about a collision until after its whole packet has been transmitted. – The reason for this is, of course, that an acknowledgment packet will only be sent after the complete packet has been received by the receiving user. – Since a collision can only occur within the propagation delay after the start of the transmission, it is a waste of time to transmit more of the packet if a collision has occurred within this period.

n

For this reason the CSMA-CD (carrier sense multiple access with collision detect) protocols have been developed. With these protocols a user keeps monitoring the channel while it is transmitting. If it detects a collision, it aborts its transmission as soon as possible thus saving time. 345

ISMA ISMA n

n

With the CSMA protocols each user must be able to detect (to sense) the transmissions of all other users. However, especially in radio channels, this may prove to be very difficult because in such channels it can easily happen that two users are hidden from each other by a building or some other obstacle. This hidden terminal problem severely degrades the performance of CSMA. As a solution the Inhibit Sense MA or ISMA (also called the BTMA, busy tone multiple access) protocol is proposed.

346

ISMA ISMA n

The ISMA protocol is identical to the CSMA protocol except for the way in which the users sense the channel for transmissions of other users. – In CSMA the sensing is done by listening to the channel on which the users transmit. – In ISMA there is a base station that transmits a busy/idle signal on a separate channel to indicate the presence or absence of a transmission of one of the users.

RACH is Busy/Idle 347

ISMA ISMA (cont.) (cont.) n

The channel on which the users transmit to the base station is called the inbound channel and the channel on which the base station broadcasts to the users is called the outbound channel. – As soon as the base station receives a transmission from a user on the inbound channel, it will generate a busy signal on the outbound channel. – If the transmission ends, the base station will transmit an idle signal. – Now if two users are hidden from each other but not from the base station they will still be able to determine if the other user is transmitting or not. 348

Random Random Access Access With With Reservation Reservation n

n

The difference between a reservation protocol and a pure random access protocol arises when a user successfully transmits its first packet in a row of packets. Now a fixed part of the channel capacity is allocated to the user for the transmissions of the rest of the packets. The user obtains a reservation. All users are aware of what parts of the channel are allocated to the reserved users. Therefore the transmissions of these users are carried out without contention, and the transmissions are scheduled. 349

RA RA with with Reservation Reservation (cont.) (cont.) n

n

n

n

Once a user has transmitted its whole row of packets, it will return the allocated capacity (give up its reservation) so it can be used by other users. If the user wants to transmit a new row of packets, the first packet will again have to contend for the channel. There are many protocols that fall within the category of random access with reservation. Many of those protocols (probably most) use slotted ALOHA as the random access method to obtain a reservation. These protocols are collectively known as the reservation ALOHA or r-ALOHA protocols

350

Chapter Chapter 3: 3: n

Review of Probability Theory – Review of Basic Probability Concepts – Useful Distributions – Basics of Statistical Methods

n

Basic Traffic Model – – – –

n

Arrival Process, Erlang and Blocking Definition Queuing Strategy and Markov Chain Formulation Erlang B, C and Poisson Models and Calculations

Contention Based Multiple Access Protocols – P-ALOHA and S-ALOHA – CSMA and ISMA

n n

Subscriber Forecast and Demographic Analysis Summary and Discussions 351

Joint Radio & Traffic Design n

n

In principle radio coverage and traffic distribution are to be considered jointly. However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity requirements deriving from the traffic forecasting.

n

n

These two very strictly dependent steps are iterated until a satisfactory solution is derived. The factors conditioning the resulting cell layout come from either propagation or traffic constraints, depending on the most critical conditions.

352

Traffic Analysis n n

n

n

As for the traffic modeling, the service area must be characterized based on subscribers' density and distribution. Geographical maps or territorial databases are utilized to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution. In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.

353

Subscriber Subscriber Forecast Forecast n

Demographics

n

– Service Penetration – Total Number of Subscribers – Distribution of Subscribers n

– – – –

Mobility of subscribers – Handoff Rates – Location Update Rate

Service Types and percentages

n

Voice Short Messages Fax Later on: Data/Internet Transactions.....

Service Statistics – Average Call Duration – Erlangs/Sub – Outgoing vs. Incoming Call Ratios.....

354

Demographics Demographics Analysis Analysis n

n

Demographics Analysis is predicting the subscribers density in different areas based on demographic data such as – Population Density, ( Layered by Age Classes) – Income Distribution – Household Distribution – Highways and Vehicular Traffic Distribution – Business Area Maps The estimate is usually obtained by a weighted combination of these distributions .

$$$ $$$$$ $$ $ $

355

Demographics Demographics Analysis Analysis Vehicular Traffic Dist.

Population Dist.

Income Dist.

%50

%0

%25

%25

%30

%20

%0

%50

%25

%25

%10

%40

W2 W1

W3

%?

%? Subscribers Dist.

%?

%? 356

Subs/Cell Subs/Cell

Subscriber Distribution Map

Composite Coverage Design (Cell Footprints)

357

Alternative Subscriber Forecast Total Population Service Penetration Factor

Total No. of Subscribers

LBA

Market Area

Subscribers’ Density

MAPL

Prop. Model

Cell Area

# Subs/Cell

358

Traffic Analysis for BTS

# Subs/Cell

Erlang/Subs

Erlangs/Cell

Erlangs Model

Voice Channels/Cell

GoS

Channelization

RF Channels/Cell 359

Chapter Chapter 3: 3: Review Review and and Discussions Discussions

Review of Probability Traffic Models Erlang Calculation Random Access Subscriber Forecast

360

Chapter Chapter 4. 4. n

Introduction:

» Planning Process, Objectives and Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 361

Day 4: Network planning n

Introduction » Planning Process, Objectives and Concepts

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations » Availability and Utilization

362

Scope of Fixed Network planning n

n

n

The scope of Fixed Network Planning (FNP) covers the dimensioning and planning of the NSS and part of BSS network elements and their interconnections. FNP is not the same as RF planning or cell site planning, but it requires input from it. Objective: – The primary network planning objective is to design a network that offers a desired set of communication services at a specific performance and acceptable cost over a period of time. 363

Planning Considerations n

How to best balance CPRS – Cost » Operations » Maintenance » Expandability

– Performance » Fast response

– Reliability » Availability .01 down » Fault tolerance

– Service » Latest features (now and future) 364

Objectives and Constraints n

Objectives: – Business Objective » Time to Market, Competitive price and services

– Technical Objective » performance and reliability » Services and Quality of Service » Quality n

Constraints – – – –

Time/Resources Cost Technology Network Elements limitations 365

Growth

n

n

The future network capacity/growth is based on the validity of the current measurement and statistical analysis under growth conditions. The future capacity calculation depends on the traffic pattern and traffic sensitivity. – Current traffic patterns are scaleable to estimate the future. For Example: » Future (2 years from now) average number of call attempts = current average number of call attempts * (1 + growth ) **2.

– -And each elements voice or signaling traffic characteristics will not change. 366

Data Data services services growth growth n

The growth rate of Data services will have an impact on Fixed Network planning. – Some operators believe their Mobile data may account for 12-15% of Revenue by 2000. – And 10 -15% of the GSM users will be data users by year 2000. – This rate of growth will equate to 20-25% of the traffic on the GSM network.

n

The impact of the data services – Circuit switch Data Impacts » MSC/VLR and the Control channels

– Packet Switch Impacts » IWF and the control channel usage 367

Mobility Impact on Planning

n

In a none mobile environment the planning process is trivial. Where the growth of the subscribers and call setup have is a linear function In a Mobile environment as the number of the subscribers/cells grow the load from mobility registration, HO will grow none linear, while the call setup load continue to be a linear function . Registration and HO Call setup

load system Mobile

n

Number of subscribers 368

Network Design Activity n

n

Setting Business Objective – determine subscriber growth – Establish planning interval – Target new services – Decrease cost /sub Network service Requirements

– Specify the requirements for services and the network

n

RF Engineering

– Plan the Cell Sites and Optimize the topology for Maximum coverage

n

Network engineering/ Network capacity /reliability – – – –

Service Planning Capacity /Performance Planning Availability Planning Cost Planning 369

Planning Issues n

Service Planning – Based on the service being provided by the GSM network, must define all aspect of the services including the Quality of Service that affects the technical objectives

n

Capacity /Performance Planning – Characterize the offered traffic for each element based on » Traffic Model and Mobility Model » Call Mix Model and Service Mix Model

n

Availability Planning – A hard number that must be given to the network planner for each network element. % availability

n

Cost Planning – Perform a cost analysis on each alternative proposed. 370

Alternatives

n

n

n

n n n

Alternative network plans must be devised until the overall objectives are satisfied Provide as many alternative as possible, if required breakdown the alternatives into phases for a given period. comparative analysis of alternatives provides the basis for selection Real measured data is preferable to estimates A quantitative basis for selection is preferable Acquire tools and models for various aspects of the network.

371

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 372

Modeling Concepts n

n

A model provides a structure to describe the elements of the planning problem, their relationships, the type of information required, the methods of analysis to use. Models can be either – Logical (functional) » Switching » Database HLR/VLR » Protocols

– Computational (quantitative) based on analytical and simulation » Traffic and Queuing Model » Mobility Model 373

Analytical vs. Simulation n

For Analytical model: the randomness of the events is described by equations describing probability distribution – can provide quick results, using spreadsheets and software scripts.

n

For simulation model: the randomness of the events is described by algorithms that simulate the probability distribution (Monte Carlo). – The accuracy of the result depends on number of runs and granularity 374

Purpose of Models n

Network Capacity/ Performance Model purpose – For a given network architecture, models each element utilization as offered traffic increases due to subscribers growth, new services and increase use. – Computes the required number of network elements to meet performance objective

n

Availability Model – From statistical data collected shows the system availability as minutes of outage/week/months etc. – Determines average service availability to the end user.

n

Functional Model – Network diagram showing all the elements to support the services

n

Cost Model – For a given network architecture and growth estimate based on the network capacity model computes the capital cost for the planning interval. 375

Two Types of Traffic n

The traffic capacity of the wireline/wireless network can be categorized as – Voice/Data traffic (Erlang traffic) – Control/Signaling traffic (events traffic)

n

n

The signaling traffic capacity calculation is based on occurrence of an event , Call Attempt (CA)and does not involve the duration of the call, where as calculation of the voice traffic considers the duration (Erlang) and the measurement of the voice traffic is based on Erlang B(blocked calls are not retried).

376

Logically Different Paths n

The signaling traffic will impact – – – –

n

The Signaling links The Databases (HLR/VLR) Data storage Computer hardware (processors)

The voice traffic will impact – The Transcoder – The Switch/ voice trunk – Voice Mail

377

Signaling Traffic n

Following events have major impact on the traffic calculations and processor utilization. – – – – – – – –

Call Origination Call Termination Authentication Handover Location Update IMSI Attach/Detach SMS Services Data Services 378

HO impact n

No of HO/CA can impact many areas of the system – Inter BSC HO, intra-MSC HO » The BSC and the MSC Call Processing

– Intra-BSC HO » The BSC call processing » No effect on MSC (depending on implementation)

– Inter MSC HO (Anchor MSC) » MSC » BSC

379

Location Update n

Possible location update procedures: – MS location update to MSC/VLR – HLR updating of the location at the MSC/VLR request – Removal of the subscriber record from MSC/VLR at the HLR request – Periodic location update is performed to keep the MSC/VLR and HLR in check when a failure occurs on any of the elements. » The period can be controlled by the operator

380

Traffic Model n

n

n

The traffic Models are based on two factors – Experiences/measurement from existing systems – Assumptions, some arbitrary All the traffic data varies in time – Subscriber’s use – New features – New elements supporting the features A traffic model with peak busy hour must be used

381

Traffic Model n

Traffic model includes – GOS or blocking factor (Grade Of Service or blocking probability) – Busy Hour Call Attempts (BHCA) /sub. – Erlang /sub – No of subscribers and the growth over the planning period

n

Example: Parameter GoS, Air Interface GoS, BSC-MSC GoS, MSC-PSTN BHCA/sub Duration of a call Erlang/sub Growth of the subscribers

Value 2% 0.1% 0.01% 1.5 (assume all active mobiles) 120 sec .05 20%/yr 382

Mobility Mobility & & Handover Handover n

n

n

Handover rates and location updating rates depend on the movements of the users. The estimation of this signaling load must be based on statistics concerning these movements. To give an idea on the order of magnitude, we can make very simple assumptions. – First we will take the assumption that the speed of 70% of the users is zero, and that the speed of the other 30% is 30 km/h. – Then, we will assume an average cell diameter of 3 km. and translate this into a mean lifetime in a cell for the moving users of 4.5 minutes, that is to say an average of around one handover every two communications. 383

Mobility Mobility & & Location Location Update Update n

A related point is the location updating traffic. Different reasons may lead to location updating, – movements of users between cells, – switch on and off, – periodic updating.

n

While the two last terms can be considered roughly proportional to the traffic in the cell (within a given traffic model), the first one varies from 0 to a high value depending on the proportion of the boundary' of the cell which corresponds to a boundary between location areas. 384

Mobility Model

n

Average User’s Speed Average Cells Size Average Location Area Size Location Update Times

n

Example*

n n n

n n

No of HO per call Ratio of Location Update (LU) to calls

Parameter No of HO /call Intra MSC HO • Intra BSC HO • InterBSC HO InterMSC HO Ratio of LU to Call • intra VLR • inter VLR

Value 2 80% 80% 20% 20% 1.8 80% 20%

385

Call Mix Model n

Call Mix Consists of – – – –

Mobile Origination Call (MOC) % Mobile Termination Call (MTC) % Mobile to Mobile (MTM) Attempts % Mobile Call Completion %

Example: Parameter MOC(M-L) MTM(M-M) MTC(L-M)

Value 60% 5% 35%

Completion %70 %40 %40 386

Service Mix Model n n

Service Mix Model includes the probability of using various services per user per call. For example

Parameter Ratio of SMS per call Fax/Data Calls Ratio of Voice Mail per call

Value 0.1 0.05 0.1

387

Transactions Transactions Callsetup/clearing Handover Location Update SMS Paging

#of MSC->BSC 5M/30O 4M/ 37O 5M/30O 7M/30-126O 1M/30O

#of BSC->MSC 6M/26O 5M/38O 6M/26O 7M/30-126O*

* The SMS message size can varyand depending the use #Messages(M) # Octetson(O) n

Other Transactions include mobile station attach/detach procedures. 388

Processes in Network Elements n

n

Each of fixed network elements perform one or all of the following processes/functions There is a capacity or limit for each process or function DATABASE

I/O Communications (Data link)

APPLICATION Call processing, Mobility

ADMINISTRATION, O&M (Billing, User Interaction)

389

Capacity Limits n

n

n

n

The Maximum network capacity (voice/signaling) is given for each network element. Each element system limit is provided for future expansions/ (Max number of processors) For a voice sensitive element/link ( ie. MSC, MC) maximum number of – Erlangs – Subscribers – Trunks For a signaling sensitive element (HLR, VLR,SM_SC) maximum number of – Transactions/Sec – Data links – Subscribers

390

NSS Elements Limits n

The BSC limits are: – – – –

n

Maximum no of BTS that can be supported/controlled Maximum no of Call Attempt (CA) Maximum no of voice ports it can support (I/O) Maximum no of Signaling link can be supported

The MSC limits are: – – – –

Maximum no of BSC that can be supported/controlled Maximum no of Call Attempt (CA) Maximum no of voice ports it can support (I/O) Maximum no of Signaling link can be supported

391

NSS Elements Limits (cont.) n

The VLR limits are: – Maximum no of subscribers (Size of the Memory!) – Maximum no of transaction/sec processing on the VLR database

n

The HLR limits are: – Maximum no of subscribers (Size of Memory ) – Maximum no of Signaling link can be supported – Maximum no of transaction/sec processing on the VLR database

392

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 393

Calculating BH Call Attempt n

n

BHCA is the rate of call attempts, both mobile originated or terminated, per unit of time during peak traffic hours. CA rate can be calculated from Erlangs A, and Average Service Time or Call Duration µ CA = Erlang / Average Call Duration A Number of Calls / sec = = A× µ 1 / µ ( in sec onds )

394

Transactions/sec n

n

n

For each network element, e.g. MSC and HLR, the number of transactions per second is the summations of the number of transactions/call attempt for all truncations involving that element Times the number of CA/sec

N Tranactions / CA = PSMS + PLoc +.... N Tranactions / sec = N Tranactions × CA / sec » P SMS = No. SMS/Call Ratio » P Loc = No.Location Updates/Call

395

Signaling Octets/sec # Oct ./Call = N S /C × LS /C + PSMS × ( N SMS × LSMS + M SMS ) + PLoc × N Loc × LLoc # Octets / sec = # Octets / Call × No. Calls / Sec ( i . e . λ ) Signaling Rate = RS = No. bits / sec = # Octets / sec × 8 bits / byte » » » » » » » » » »

N S/C = No. of call setup/clearing messages L S/C = Average message size of call setup/clearing P SMS = No. SMS/Call Ratio N SMS = No. of SMS messages L SMS = Average message size for SMS M SMS = Average Data size for SMS P Loc = No.Location Updates/Call N Loc = No of Location Update messages L Loc = Average message size for Location Update R S = Signaling Rate bits/sec

396

#of Signaling Channels RS NE0 = 64 kbps × U » R S = Signaling Rate bits/sec » N E0 = No. of 64kbps E0 channels needed » U =Utilization of the Link

397

Link Utilization n n

n

Each signaling capacity is designated as 64 Kbit sec (E0). The signaling link capacity is consumed by control information as well as the application data. When calculating the number of signaling links it is important to factor in the control and overhead information and plan for less than the maximum rate (64 K). Usually a link utilization factor is used : – For LAPD Abis link this utilization is 75% to 80% of maximum rate. – For SS7 links the utilization is 20% . (SS7 links load share/redundancy and we should count for link failures)

398

SS7 Link General Rules: F-links n

When planning For a SS7 F-link – Number of links

RS N = 64 kbps × U

– If number of links = 1 then add 1; minimum of 2 link /link set – Configure one linkset with the number of links

399

SS7 -link SS7 Link Link General General Rules: Rules: A A-link n

For a SS7 A- link – Number of links

RS N = 64 kbps × U

– If number of links are < 1 or odd add a 1 and then – Number of links per link set = Number of links / 2 – Plan for 2 link sets each to an STP pair and configure the link set as a combined link set

400

Exercise Exercise

401

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 402

Joint Radio & Traffic Design (Rev.) n

n

In principle radio coverage and traffic distribution are to be considered jointly. However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity requirements deriving from the traffic forecasting.

n

n

These two very strictly dependent steps are iterated until a satisfactory solution is derived. The factors conditioning the resulting cell layout come from either propagation or traffic constraints, depending on the most critical conditions.

403

Traffic Analysis n n

n

n

As for the traffic modeling, the PCS service area must be characterized based on subscribers' density and distribution. Geographical maps or territorial databases are utilized to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution. In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.

404

Subscriber Forecast Total Population PCS Market Penetration Factor

Total No. of Subscribers

LBA

Market Area

Subscribers’ Density

MAPL

Prop. Model

Cell Area

# Subs/Cell

405

BTS Traffic Analysis

# Subs/Cell

Erlang/Subs

Erlangs/Cell

Erlangs Model

Voice Channels/Cell

GoS

Channelization

RF Channels/Cell 406

BTS Dimensioning n

Step 1:

B T S

– For each sector estimate the required number of » traffic channels (TCH’s) » control channels (BCCH, CCCH and SDCCH) to support TCH’s

– RF channels or TRX’s / BTS – Perform Feasibility Analysis Against Limitation n

Step 2: – For the entire BTS » estimate the total number of E0 channels needed » estimate #E1’s/BTS or #BTS’s/E1 !!!

407

BTS Dim. Voice Channels n

B T S

Step 1: review # Subs/Cell

Erlang/Subs

Erlangs/Cell

Erlangs Model

GoS

Voice Channels/Sector

408

BTS Dim. Control Channels n

n

The required number of BCCH, CCCH and A=SDCCCH channels have to be estimated The number of air interface forward control channels required depends on the rates of: – – – –

n

B T S

Pages Location Updates Short Messages Call Setups

Only the numbers of pages and access grants affects the CCCH. The other information uses SDCCH. Voice Channels/Sector

Control Channels/Sector

Total RF channels

409

Number Number of of CCCH’s CCCH’s n

n

Each CCCH block can carry one message, hence the capacity of 4.25 messages/sec. The AGCH can carry – immediate assignment message for upto 2 users or – immediate assignment reject message for upto 4 users.

n

n

Each PCH message can carry pages for upto 4 MS’s using TMSI or 2 MS’s using IMSI. It is usually assumed that once the down link CCCH is correctly dimensioned the uplink RACH capacity is sufficient. 410

Number Number of of CCCH’s CCCH’s (Cont.) (Cont.) n

n

Paging parameters, e.g. the number of paging groups. (Trade Off?) Access parameters, e.g. maximum number of MS reattempts, Waiting time between Reattempts. N CCCH = ( N AGCH + N PCH ) / U CCCH where N AGCH N PCH

( λC + λ Loc + λ SMS ) calls / sec = ( 2 calls / msg × ( 4.25 msg / sec) / blk )

p calls / sec = ( 2 calls / msg × ( 4.25 mess / sec) / blk )

411

No. No. SDCCH’s SDCCH’s n

n

SDCCH carries a large portion of call setup messaging, therefore SDCCH dimensioning is an important part of BTS planning process. The number of required SDCCH’s depends on the – Call Attempt rates (MO and MT) – Location Updates and – SMS rate (Which SMS’s go to SDCCH?)

CA Rate

Loc. Update Rate

SMS Rate

N SDCCH = λC × TC + λ Loc × TLoc + λSMS × TSMS Avg. Call Setup Time

Avg. Loc. Update Time Duration

Avg. SMS Time Duration 412

Control Control Channel Channel Configurations Configurations n

There are three configurations of the control channels. – A combined Control Channel » 1 BCCH+3 CCCH + 4 SDCCH

– Non-Combined Control Channel » 1 BCCH + 9 CCCH (no SDCCH)

– SDCCH Channel » 8 SDCCH n n

If the CCCH has a low traffic requirement, the CCCH can share its time slot with SDCCHs. At least one of the first two configurations is needed. (Why?) 413

Control Control Channel Channel Assignments Assignments n

n

n

Typically the first control channel assigned comprises one BCCH, 3 CCCHs and 4 SDCCHs. When subscriber growth demands for additional control channels 8 SDCCH may be added to a second time slot to give a total of 12 SDCCH’s Also the configuration on the first channel may change to provide no SDCCH’s, resulting in the total of 8 SDCCH and 9 CCCH.

414

BTS Dim. Control Channels n

Number of Control channel required

#TRX’s 1

#TCH’s 7

#Erlangs 2.94

#SDDCH’s 4

2 3 4

14 22 30

6.2 14.9 21.9

8 8 12

5

38

29.2

12

6 7 8

45 53 61

35.6 43.1 50.6

16 16 20

9

69

58.2

20

10

77

65.8

20

Note: CBCH uses one SDCCH

B T S

Use of Time Slots TS0 Other TS’s 1 BCCH+ 3CCCH+4SDCCH 1BCCH+9CCCH 8 SDDCH 1BCCH+9CCCH 8 SDCCH 1BCCH+ 8 SDCCH 3CCCH+4SDCCH 1BCCH+ 8 SDCCH 3CCCH+4SDCCH 1BCCH+9CCCH 2 x 8 SDCCH 1BCCH+9CCCH 2 x 8 SDCCH 1BCCH+ 2 x 8 SDCCH 3CCCH+4SDCCH 1BCCH+ 2 x 8 SDCCH 3CCCH+4SDCCH 1BCCH+ 2 x 8 SDCCH 3CCCH+4SDCCH 415

BTS Dim. : Number of TRX’s n

B T S

The maximum number of RF Channels per BTS is limited by: – Manufacturers Hardware Limitations – Avaliable Spectrum and Target Reuse factor

n

n

If the numbers RF’s needed is not feasible cell splitting or more sectorization may be needed. At the end of this step all BTS’s should have acceptable number of RF channels. Voice Channels/Sector

Control Channels/Sector

Total RF channels

416

Step 2: Backhaul Consideration n

Add the number of TCH’s needed on all sectors and calculate the numbers of E0’s needed. – If TRAU is at the BTS » # E0 Channels = # TCH’s

– If TRAU is at BSC or MSC » # E0 Channels = # TCH’s/4, rounded up n

n

Add One or two E0’s for Signaling/Control Information, or wait till next section!! Estimate the number of E1’s needed » Total # E0 channels/30 = # E1 links 417

Step 2: n

If #E0/30 > 1 – more than one E1 is needed – One may limit the #E1/BTS to one. In such a case the number of TCH’s per BTS may be limited by E1 capacity, i.e. roughly 28*4=112 TCH’s per BTS.

n

If #E0/30 < 1 – Multiple BTS’s may be connected in a Daisy Chain Configuration.

B T S

B T S

B T S

BSC

418

Exercise Exercise

419

Exercise Exercise n n n

The cell design in a cellular market is based on the following assumptions, The total number of subscribers is projected to be 100,000. the subcriber usage and grade of service in regions A and B are different. – Case 1: Each of regions A and B are covered by 50 BTS’s, uniformly distributed. Find the number of TRX’s needed for each BTS in regions A and B. – Case 2: Assuming the maximum number of TRX’s per BTS is 3, find the minimum number of BTS’s needed to support the traffic in this market.

Traffic Paramters Erlangs/Subs GoS

Region A

Region B

Region A

50mA/sub 20mA/sub %1 %2

Demographics Distributions Population Income Vehicular Traffic

Weighing Factor 0.5 0.3 0.2

Region B Region A

Region B

%40 %80 %50

%60 %20 %50

420

Exercise: Exercise: Case Case 11 Demographics Distributions Population Income Vehicular Traffic

Weighing Factor 0.5 0.3 0.2

Region A Region B %40 %80 %50

%60 %20 %50

Average Percentage of subscribers No. of subscribers in each region Total Erlangs in Each Region Erlangs/BTS Number of TRX’s/BTS

421

Exercise: Exercise: Case Case 22 Demographics Distributions Population Income Vehicular Traffic

Weighing Factor 0.5 0.3 0.2

Region A Region B %40 %80 %50

%60 %20 %50

Average Percentage of subscribers No. of subscribers in each region Total Erlangs in Each Region Maximum Erlangs per BTS Number of BTS’s

422

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 423

BSC interfaces Review n

BSC <-> BTS BTS1 BTS2 BTSn – Voice Ports (E1 trunk) – Abis Ports (64kpbs LAPD link)

n

BSC <-> MSC/VLR – Voice Ports (E1 trunk) – A link (64kbps SS7 F link)

n

BSC

BSC <-> OMC (R) – Data link (X.25 data link) OMC MSC 424

BSC <=> BTS Link n

n

No of the voice ports (E0) required between the BTS(s) and BSC is determined by the BTS and the traffic channels allocated for the offered traffic. The of number of signaling link required can be derived form the number of traffic channels allocated.

B T S

BSC

– Normally an E0 link will be sufficient to carry the maximum voice/signaling data to/from a BTS. 425

BSC <=> BTS Voice Ports If TRAU is at the BTS

n

– Total voice ports = total TCH used by the BTS (all of the sectors)

If TRAU is at BSC or MSC

n

– Total voice ports = total TCH used by the BTS (all of the sectors)/ 4, rounded up! n

It is possible that a full E1 link may not be required by a BTS in this case BTS’s can be connected to E1 in Daisy Chain Configuration.

B T S

BSC

426

BSC <=> BTS Signaling Ports n

The number of Abis signaling links can be determined from – BHCA or call arrival rate obtained from » Total Erlangs From all BTS sectors to BSC » and Average Call Duration

– Number of SMS and Location Updates /Call – Abis Message Sizes B T S

BSC

427

BTS<=>BSC Signaling Ports No. Bytes / Call = 1 × N S /C × LS /C + PSMS × ( N SMS × L SMS + M SMS ) + + PLoc × N Loc × L Loc + PHO × N HO × LHO RS = No. Bytes / Call × 8 bits / byte × No. Calls / Sec ( i . e . λ) RS N E0 = 64 kbps × U Abis n n n n n n n

N S/C = No. of call setup/clearing messages L S/C = Average message size of call setup/clearing P SMS = No. SMS/Call Ratio N SMS = No. of SMS messages L SMS = Average message size for SMS M SMS = Average SMS data size P Loc = No.Location Updates/Call

n n n n n n n

N Loc = No of Location Update messages L Loc = Average message size for Location Update N HO = No of Handoff’s L HO = Average message size of Handoff’s R S = Signaling Rate bits/sec N E0 = No. of 64kbps E0 channels needed U Abis =Utilization of the Abis Link 428

BSC<=>MSC/VLR: Voice Ports n n

n

Aggregate the Erlang from all of the BTS’s, call it eBTS-BSC Perform an Erlang B look up with a GoS of BSC (usually smaller than BTS GOS) and eBTS-BSC to determine the number of voice channels required. from number of Voice Channels find the number of E0 channels needed – If TRAU is at the BSC # E0’s = # Voice CH’s – If TRAU is at the MSC # E0’s = # Voice CH’s/4, rounded up BTS1

e1

e2 BTS2

en BTS2

B S C

eBTS-MSC

TRAU

MSC 429

BSC<=> MSC/VLR Signaling link No. Bytes / Call = 1 × N S / C × LS / C + PSMS × ( N SMS × LSMS + M SMS ) + + PLoc × N Loc × LLoc + PHO × N HO × LHO RS = No. Bytes / Call × 8 bits / byte × No. Calls / Sec (i. e. λ ) RS NE0 = 64 kbps × U A n n n n n n n

N S/C = No. of call setup/clearing messages L S/C = Average message size of call setup/clearing P SMS = No. SMS/Call Ratio N SMS = No. of SMS messages L SMS = Average message size for SMS M SMS = Aveage SMS data size. P Loc = No.Location Updates/Call

n n

n n

n n n

N Loc = No of Location Update messages L Loc = Average message size for Location Update N HO = No of Handoff’s L HO = Average message size for Handoff’s R S = Signaling Rate bits/sec N E0 = No. of 64kbps E0 channels needed U A =Utilization of the A Link

Note that these messages sizes are not the same as Abis link messages. (Why?)

430

BSC <-> OMC(R) n

n

n n n

The data interface between the BSC and OMC is based on the X.25 data protocol. A single X.25 data link can be planned for this OMC interface. The capacity of this link depends on the BSC sizing and number of BTSs connected. 19.9kbps or higher is recommended Usually a 64kbps E0 link is sufficient. The connection from BSC to OMC may be indirect through MSC. BSC OMC 431

BSC Dimensioning (review) n

n

The BSC capacity in general is Its ability to connect to and process information received by all the signaling links from BTS(s), MSC and OMC. This capacity is usually expressed in terms of – – – –

Max_BTS: Total No of BTS that can be supported/controlled, Max_TRX: Maximum number of TRX’s in the connected BTS’s. Max_CA: Maximum number of CA Max_PORT: Total Number of Ports, (input and output together)

OMC B T S

B T S

BSC

B T S

MSC/VLR

432

BSC Dimensioning n

For a given system once all of the trunk traffic to the BSC has been identified the capacity requirement can be determined. – – – – –

n

The Total Erlang (or BHCA) from all of the BTS < Max_CA The total number of ports required by the BSC< Max_PORT Number of Connected BTS’s < Max_BTS Number of TRX’s on Connected BTS’s < Max_TRX The total number of Signaling links < Maximum No. of signaling links supported

Once the capacity and performance requirement has been identified the equipment (no of boards etc.) can be determined.

433

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 434

MSC/VLR Interfaces n

MSC/VLR voice interfaces – – – –

n

BSC’s MSCs PSTN MC (VMS)

Other BSC’s MSC2 MC EIR

MSC/VLR signaling link interfaces

– BSC’s – SS7 Network (Redundant SS7 A-link) » HLR/AC » SM-gateway – PSTN (SS7 ISUP Signaling) – MSC (SS7 F-link) SS7 Network

n n

EIR (SS7 F-link) OMC (X.25 link)

HLR/AC

MSC

OMC

PSTN SM-GW 435

MSC/VLR <-> BSC Voice Ports n

The Number of MSC ports, needed for MSC to BSC voice transmissions is the sum of all E0 channels from all of the BSCs Nports = NBSC1 + NBSC2 +...+ NBSCn BSC2 BSC3 BSC1

BSCn MSC

436

MSC/VLR <-> MSC Voice Ports n

MSC/VLR <->MSC » » » »

n

Voice trunks are required between MSCs to support MTM calls without routing the call to the PSTN inter MSC HO MC traffic across MSC’s

Initially an E1 link will be planned between each MSC pair which are subject to inter MSC handover. MSC1 MSC2

437

MSC/VLR<->PSTN n

The Number of Voice Ports can be determine from – Total erlangs from all of the BSCs (already calculated) – GoS from the traffic model – Erlang B table eBSC1

MSC

eBSC2 eBSCn

GoSMSC

P S T N 438

MSC/VLR<->MC (VMS) n

The Number of voice ports can be estimated using the – Incoming Erlang to MC, which is the product of » % of calls terminating to voice mail which is • % of subscribers provisioned for the service times • % of subscribers either not answering the call or call forwarded the calls

» Total incoming erlangs to the switch* % of call terminated to voice mail

– With GoS of VMS = 0.01 % – Erlang B

MC MSC

439

MSC/VLR Signaling links n

n

n

The SS7 backbone has been planned and designed (assumption here is that an existing network is used). And that the SS7 network is designed to handle the traffic from the PLMN that is being planned. Planning a fix SS7 packet network is a major task. Many large operators design their own SS7 network (STPs).

440

MSC/VLR<->BSC A Signaling Link n

To determine the total no of MSC-BSC signaling links required add the numbers of links from each BSC from earlier calculations. BSC2 BSC3 BSC1

BSCn MSC

441

MSC/VLR <->SS7 Network n

n

To determine the number of links required for connection to the SS7 network must calculate the following: The sum of the signaling traffic – To/from the HLR-AC – To/from SM gateway – To/from the MSCs outside the network is required.(this is considered negligible)

MSC

SS7 Network

HLR/AC

SM-GW

442

HLR transactions n

Traffic to/from HLR-AC is calculated base on the following transactions Authentication Termination Location Updating SMS messages (send routing information, Set Message Waiting etc.) – HLR Interrogation – – – –

HLR/AC

443

HLR transactions: Authentication n

No of octet/sec to/from HLR related to Authentication is computed in two steps: – Calculate total #authentication transactions/sec » Assuming authentication is performed n=1 times every CA » Total no of Auth transactions/sec = total CA /sec * n

– Calculate total number of Auth octets/sec » Total no of octet for Auth/sec = 2 Message per transactions* 30 Octet per message * total no of Auth transactions/sec

444

HLR transaction: Terminations n

No of octet for to/from the HLR related to Termination is computed in two steps: – Calculate total #termination transactions/sec » Total no of terminations transactions /sec = • Total CA/sec *( MCM + MTM)%

– Calculate total #termination octets/sec » Total no of termination octets /sec = • total No of Termination transactions/sec * • 2 message per transaction * • 30 octet per message

445

HLR Trans. : Location Updates n

No of octet for to/from the HLR related to Location Update is computed in two steps: – Calculate total number of Location Update transactions • Total no of Location Update transactions /sec = Total CA/sec * Ratio of Location Updates

– Calculate total number of Location Update octets/sec • Total no of location update octets/sec = total no of location update transactions/sec * call attempts * 2 messages call attempts * 25 octet per message 446

HLR transactions: SMS

n

No of octet for to/from the HLR related to MT and MO SMS is computed in two steps: – Calculate total number of SMS transactions » Total no of SMS transactions /sec = Total CA/sec * Ratio of SMS

– Calculate total number of SMS octets/sec » Total no of SMS octets/sec = Total no of SMS transactions /sec * 2 Messages per call * of 33 octet per message 447

SM-gateway transactions Traffic to/from SM gateway n

n

The SMS Gateway will support both the MO SMS as well as MT SMS services. To calculate the number of octet to/from SMgateway – Calculate total number of SM gateway transactions/sec » Total no of SM gateway transactions/sec = Ratios of SMS calls * CA/sec

– Calculate total number of SM gateway octets » Total no of SM gateway octets/sec = Total number of SM gateway transactions/sec * 2 message per call * 100 octet per message 448

Signaling Rate on MSC-SS7 Links n

The total MSC transactions/sec is the sum of – – – – –

n

Total number of SM gateway transactions/sec Total no of Auth transactions/sec Total no of Terminations transactions /sec Total no of Location Update transactions /sec Total no of SMS transactions/sec

The total no of octets/sec is the sum of – – – – –

Total no of SM-gateway octets/sec Total no of Auth octet/ sec Total no of Termination octets/sec Total no of Location Update octets/sec Total no of SMS octets/sec 449

MSC/VLR<->SS7 network n

No of MSC signaling links to SS7 network is

Octets / sec × 8 N = 64 kbps × U A n

Since this is an SS7 A-link connection, a pair of link set is required to each STP pair. Follow the SS7 link rules to determine no of links required. MSC

SS7 Network

HLR/AC

SM-GW

450

MSC/VLR PSTN signaling link n

To calculate the no of SS7 ISUP links required – Determine No of ISUP messages per call attempts » Assume 5 messages

– Determine number of octets per message » Assume 25 octets per message

– 5 messages * 25 bytes/ message * No. Call attempts/sec / 64 Kbps * SS7 link utilization

Normally an SS7 F link is configured. Follow the SS7 link guide line to allocate no of links P required. S MSC

T N451

Other Connections n

The MSC/VLR-OMC interface is based on X.25 – One E0 link is sufficient to handle the traffic.

n

The MSC/VLR-EIR interface is based on the SS7 signaling and it is operator dependent. – A single SS7 E0 link is recommended. – The operators normally provide this functionality as part of OSS (Operations Sub-System).

452

MSC/VLR Dimensioning n

The MSC/VLR capacity in general is – Its ability to connect to and process information received by all the signaling links from BSC(s), HLR and OMC. – The MSC capacity usually expressed in terms of » Maximum no of BSC that can be supported/controlled (a hard value) » Maximum no of Call Attempt (CA) » Maximum no of voice ports it can support (I/O) » Maximum no of Signaling link can be supported

– The VLR capacity limits are based on » Number of subscribers (less and less of limiting factor) » Transaction/sec processing on the VLR database 453

MSC Dimensioning (cont.) n

For a given system once all of the voice port and signaling link to the MSC has been identified the size of MSC can be determined. – The total Erlang from all of the BSCs < Maximum erlang supported by the MSC – The total number of voice ports required < Maximum ports supported by the MSC – The total CA from all of the BSCs < Maximum CA supported by the MSC – The total number of signaling links required < Maximum signaling links supported by the MSC 454

MSC Dimensioning (cont.) n

The VLR limitations must also be met » Total number of subscribers < Maximum no of subscribers » Total number of transactions/sec < Maximum no of transaction/sec

n

If required traffic is greater than the MSC/VLR limits then provide different alternatives » Possible add to the number of MSCs or a plan for a larger MSC/VLR » Or if other MSCs already exist determine the possibility of sharing with the other MSCs

n

Based on the constraint select the best alternatives 455

Exercise Exercise n

n

Using the information provided in page 4-25, 4-27 and 4-28 estimate the number of signaling ports between BSC and MSC. Assuming the total Erlang at the BSC is 1000 and average call duration is 120sec. BSC

MSC 456

HLR/AC Transactions MSC MSC VLR VLR

n

Major HLR/AC transactions that effects HLR sizing – – – –

SS7 network Authentication Termination validation SM-GMSC HLR/AC Location Updating HLR/AC Subscriber provisioning (add/delete/update)

» Which is not considered for traffic calculations

– SMS messages (send routing information, Set Message Waiting etc.) – HLR Interrogation 457

HLR/AC interfaces n

n

The HLR will interface to the SS7 network via the SS7 A-link. To plan for the A-link the traffic from various elements must be considered – MSC/VLRs – SMS-gateway

n

n

Based on previous calculations ( MSC to SS7 network) determine the no of signaling link required for HLR to SS7 network. Note: the total call attempts will be the sum of call attempts from all the MSCs. 458

HLR/AC Dimensioning n

Many HLR/AC platforms can support millions of subscribers in their database. The traffic load is critical issue.

n

It is important that the HLR/AC supports the present maximum traffic and allow for growth of the number of subscribers and transactions.

n

The HLR limits are – Number of transactions/sec – Number of signaling links – Number of Subscriber 459

HLR Dimensioning

100

The total number of transactions from all the elements < Maximum number of transactions supported by the HLR

40

60

80

The Planning Limit

Porcesor 20

n

10000

20000

30000

40000

Aggregate Transactions

50000 460

Chapter Chapter 4. 4. n

Introduction:

» Planning Objectives, Concepts

n

n

Planning Inputs » Traffic, Call and Mobility Models » Basic Concepts and Calculations Dimensioning (New System) » BTS • Traffic Channels • Control Channels

n

» Links to/from BSC (Voice & Signaling) » BSC » Links to/from MSC/VLR » MSC » HLR/AC Section Summary and Discussions 461

Chapter Chapter 4: 4: Review Review and and Discussions Discussions

Planning Concepts Dimensioning Network Elements and Interconnects

462

Chapter Chapter 5. 5. n

n n

Fixed Network Configurations Rules/ Planning Options Network Expansion for Existing System Trends in GSM Networks and Future Mobile Networks – UMTS and IMT2000 Perspectives

n

Course Summary and Discussions

463

Planning/Configuration Planning/Configuration Steps Steps n

Review Inputs: – Average Size and Capacity of Links and Network Elements – BTS Locations

From Dimensioning From RF Design n

BSC Planning – Preferred Locations – BTS-BSC Configurations – BTS-BSC Assignment

n

GMSC/MSC Planning – MSC Preferred Locations – BSC-MSC assignment

n n

HLR Location, Redundant HLR OMC Location 464

Configuration Configuration

n

Once the dimensioning of the elements and link requirements have been identified consider – Where and how to lay out each element and interconnect – What kind of circuits to use for interconnect E0,E3. – Fiber v.s Microwave what is available? What is more economical? Perform cost analysis – Is it better to size the HLR based on current requirements and growth, how costly is it to expand later? – Try different interconnects. Is there a saving to be made? – Identify MSC to MSC interconnects, a ring or a star configuration. 465

Alternatives Alternatives n

Compare the alternatives you have devised based on – – – – –

n

COST Time frame Features Demand Technology

Select the best alternative and be flexible to changes (customer is right !)

466

Backbone Backbone n

n

The backbone is the transmission facility that allows the interconnects of the GSM elements via the E0/E1 links. Decide on the type of backbone, before planning any of the equipment. – This decision is mostly based on » Availability » Cost » Reliability

n

Make sure the same clock source is used for synchronization of the entire backbone 467

Transport Transport

? n

n

How to interconnect the elements in the GSM network? What facilities to use? This one of planners concerns – BTS to BSCs – BSCs to MSCs – MSCs to PSTN 468

Digital Digital Transmission Transmission n

Digital Transmission – The analog signals are sampled, coded and multiplexed into a digital bit-stream which is modulated into digital carrier (electrical, microwave or optical) – One single channel has a rate of 64 Kbs, Several voice channels are multiplexed into this bit-stream. » Voice channels sampled at the twice the rate therefore

• 4Khz * 2 * 8bits = 64Kbps. » The GSM air interface uses a vocoding (Voice coder/decoder) to compress the 4 Khz bandwidth to 8Kbps digital bits. 469

Digital Digital Transmission Transmission n

Digital hierarchy

n

– E0 64Kbps 1VC – E1 2.048Mbps – E2 8.4Mbps – E3 34.3Mbps – E4 139.2Mbs – E5 565.1Mbps Devices based on the hierarchy are Channel Bank

Voice& Other signals

Intelligent Channel Bank

30E0 4 E1 16E1 64E1 256E1

MUX

Digital Cross Connect

1 E3

E1 Flexible assignment of channels to E1s

16 E1

E1

E0

E1 470

Synchronous Synchronous Hierarchy Hierarchy n

Two standards exist ITU standard describes the Synchronous Digital Hierarchy (SDH) and the other is the North American ANSI standard that describes the Synchronous Optical NETwork (SONET) with optics rate in mind.

471

Microwave Microwave Option Option n

Provides transmission – When right of way is difficult to obtain – Rapid deployment is required

n

Available in wide range of capacities – E1 and Lower rates – SDH and SONET rates

n n

n

Wide range of frequencies Atmospheric conditions affect the quality of transmission. Sometimes less expensive than the leased lines 472

Cost Cost Analysis Analysis n

A transport network design – Fiber optic link (option 1) – Microwave lease (option 2)

n

n

From cost analysis of the two options it may be concluded that after the second year option 1 will pay for itself and a fiber optic backbone will be more cost effective in long run. List other pros and cons

473

Cost Cost analysis analysis example example This is an example of a cost analysis for a backbone network. Two options are presented, One with a leased links as an interconnect method and the other purchase of microwave radio. Assuming the following configuration for a leased line A E f

C

g D

h i

B 474

Option Option 1: 1: Leased Leased Line Line Option I :COST of leased line (assume $2856/Km)

A-i

2

5

Distance in Kms 135

A-f

1

2

35

$86K

$171K

A-g

1

2

55

$114K

$228K

A-h

1

1

70

$114K

$114K

B-C

1

100

$171K

C-D

1

30

$86K

D-E

2

265

$428K

E-A

4

200

$856K

Path

Total

No of links Launch

Year1

Amount Launch Year 1 $342K $856K

$656K

$2910K

475

Option Option 2: 2: Microwave Microwave cost cost Option II :Cost of Microwave infrastructure for 1 year Path

Distance in Kms

A-i

135

$320K

A-f

35

$80K

A-g

55

$140K

$30K

A-h

70

$140K

$30K

B-C

100

$192K

$110K

C-D

30

$64K

D-E

265

$640K

$270K

E-A Sub-total

200

$640K $2216K

$270K $900K

Total

Cost of Microwave Equipment

Cost of Tower including Royalty

$100K

$3116K

476

Analysis Analysis n

n

Obvious comparison shows the cost of leased line (option 1) for the first year is lower than the microwave cost. But the second year the microwave infrastructure pays for it self and there are other advantages : Possible earned revenue by leasing the extra bandwidth available to private network operators. – Save on leased links required for other interfaces like billing, OMC, NMS etc. – Increased system reliability, therefore satisfied customers. – No wait delay in ordering new links

477

Cell Cell Planning Planning n

n

Our assumption is that the Cell Planning has been done based on coverage, capacity and interference analysis. Do we know these steps? – coverage, – capacity and – interference analysis

478

Abis Abis Interface Interface n

n

Abis links can represent a substantial part of the running costs of a PLMN. If each BTS site requires a relatively small number of circuits, economies can be obtained if the drop and insert , or Daisy Chain connection method can be used at the BTS. – This technique provides the ability to share a 2 Mbit/s multiplex between several BTS sites, and to decrease the number of leased or installed transmission links.

479

TRAU TRAU Location Location To MS

BTS

To MS

BTS

To MS

BTS

RF Air Interface

TRAU

BSC

A-bis Interface

BSC

MSC

To Fixed Networks

TRAU

MSC

To Fixed Networks

BSC

TRAU

To Fixed Networks

A Interface

13 kbps encoded voice / 12 kbps data

16 kbps transmission

MSC

64 kbps transmission Physical site 480

Low Low and and High High Traffic Traffic Areas Areas n

n

n

n

In rural areas, most BSs are installed to provide maximum coverage rather than maximum capacity. High levels of traffic are not problems in those areas. If the cells are not colocated, the BSS will be split between BSC and BTS where BSC will then be connected to several BTSs. For high-traffic surroundings in urban areas, MSC can be connected to a number of BSSs via A-interfaces. Some of the BSSs are multicell (sectored) sites. Several groups of omnidirectional as well as sectorized BTSs may be tied into a common remote BSC via combinations of star, chain, and multidrop connections. 481

BSC BSC Location/Capacity Location/Capacity n

n

The location and capacity range of the BSCs is a debated point. – Some operators want small BSCs on the BTS sites. – Some other operators want big BSCs on the MSC sites. even possibly a single BSC per MSC. – Others want independent BSCs with a capacity intermediate between a BTS's and an MSC's, and which can potentially be sited in any location, not necessarily with a BTS or an MSC. If more than one BSC is used do not co-locate the BSC to avoid any natural disaster disturbing the operations of all of the BSCs 482

BSC BSC Location Location n

Various considerations will dictate the choice. – A BSC has three main functions: it acts as a circuit concentrator, and as such its position impacts the running costs of the transmission lines between BTSs and MSCs. – A BSC is also an operation and maintenance agent; we will see that the BTSs are not linked directly to the OSS, but through their BSC. – Finally, a BSC is where handovers are controlled. Bigger BSCs lead to a smaller number of handovers which must be handled by the MSC and the bigger the BSC the wider the knowledge concerning the traffic used to decide on handovers. 483

BSC BSC Location Location (cont.) (cont.) The list of preferred BSC location should be prepared based on n Low Cost, client owned/leased buildings. n Availability of backhaul links n Access, Utilities, Security and maintainability Considerations n Easy connection to BTS’s n Being in the center of cluster of cells, – Having BTS’s in LOS, if Microwave link are to used – Having MSC in LOS, if Microwave link are to used 484

BTS BTS to to BSC BSC Assignment Assignment n

n n

n

n

Starting from the most preferred BSC location, a group of BTS’s around a that BSC are assign to it Considering: The BSC limitations (# BTS’s, #TRX’s,.#Erlangs...) Short/easy connections, The BSC may be co-located with one of BTS’s in the middle of the cluster. Possibility of daisy chain connection of some of BTS’s using E1 or E3 links Minimization of inter-BSC handovers rates, by not leaving major highways and intersections at the boundary of BSC coverage area. 485

BSC BSC n n

n

n

Once a set of BTS’s are assigned to a BSC The total voice and signaling traffic on Abis links should be checked. At this point alternative BTS-BSC connection configurations should be of considered for best utilization of the links. Total Voice and signaling traffic from all selected BTS’s to BSC should be checked against BSC size and capacity selected as part of dimensioning.

486

BTS -BSC Configurations BTS-BSC Configurations n

There are several BTS-BSC configurations: – single site, single cell; – single site, multicell; and – multisite, multicell.

n

n

These configurations are chosen based on the rural or urban applications. These configurations make the GSM system economical since the operation has options to adapt the best layout based on the traffic requirements. System optimization is possible by the proper choice of the configurations 487

BTS -BSC Configuration BTS-BSC Configuration n

Some of BTS-BSC Configurations include – omnidirectional rural configurations where the BSC and BTS are on the same site; – chain and multidrop loop configurations in which several BTSs are controlled by a single remote BSC with a chain or ring connection topology; – rural star configurations in which several BTSs are connected by individual lines to the same BSC; and – sectorized urban configurations in which three BTSs share the same site and are controlled by either a collocated or remote BSC. 488

BTS -BSC Configurations BTS-BSC Configurations A - Interface

BTS BSC BTS

Omnidirectional Configuration BTS

BTS

A - Interface

BSC Omnidirectional Configuration BTS

BTS

BTS BTS

BTS

1

2 A - Interface

BSC Star Configuration BTS

3

A - Interface

BSC

4

Multidrop Configuration 489

BTS -BSC Configurations BTS-BSC Configurations (cont.) (cont.)

A - Interface

BTS1 BTS2 BTS3 BSC

5 Sectorized Configuration

A - Interface

BTS1 BTS2 BTS3

BTS1 BTS2 BTS3 BSC

6

Sectorized Configuration with remote BSC and MSC-BSS configuration 490

Exercise Exercise n

A cellular network consists of 100 BTS’s, 50 of which are in central downtown area and 50 of them are in the suburbs. The BTS’s are uniformly distributed. – Each BSC can handle upto 30 BTS’s. – How do you place the BSC’s and how do you assign BTS’s to BSC’s. Hwy 1

Hwy 2

491

MSC MSC n

n

n

n

The trend is to have MSCs of as high a capacity as possible with the present switch technology. Currently the order of magnitude of an MSC capacity is tens of thousands of Erlangs. For a network with a 10% penetration of the population and 0.02 Erlang per subscriber, a 2000 Erlang MSC is suitable for an area with 1000 000 inhabitants. This is commensurate with the present density of PSTN switch locations. MSCs can then be sited in rather important towns, and will cover a part of the biggest towns or a medium town and the surrounding area. 492

Distributed Distributed v.s. v.s. Centralized Centralized n

Comparison of distributed design vs. centralized – – – – – – –

Distributed design Allows for easy expansion Reliability/availability effect the system Easier to adapt to IN standard Faster introductions of services Less complex and easier to maintain (it is logically divided into sub-system) Cost More (facilities to interconnect)

Centralized Not as easy Any minor change may Harder to adopt Slower Harder to maintain Less costly

VLR VLR HLR/AC HLR/AC

MSC STP

EIR EIR

MSC/VLR/HLR/AC/EIR

493

MSC MSC Configuration Configuration n

MSC functionality – Some manufactures of the MSCs can provide one or all of the following functionality within the MSC platform » VLR, MSC, HLR, EIR, STP in addition to SSP functionality

n

When considering small PLMN network (less than 3 MSCs) it is more economical and efficient to design a non distributed (centralized) system.

494

MSC MSC Locations Locations n

n

Generate a list of best candidates for MSC locations, considering: The required number of MSC’s predicted (as part of Dimensioning), consider centralized and distributed options separately. – Low Cost, client owned/leased buildings. – Availability of links to PSTN – Access, Utilities, Security and maintainability Considerations – Possibility of Expansion – Easy connection to BSC’s 495

Low Low Cost Cost Configuration Configuration Options Options CO

MSC CO

CO

BSC

BSC CO

CO

CO

CO CO BSC

496

MSC MSC Configuration Configuration n n

n

n

Normally the MSC and VLR functionality are combined. One MSC within the PLMN must perform Gateway functionality to route the incoming calls from PSTN to the MSC/VLR Plan to have MSCs of as high a capacity as possible for a given number of subscriber and BHCA. Depending on the services provided plan to support IWF and SM gateway interfaces/functionality. 497

MSC/VLR MSC/VLR interconnects interconnects n

The system interconnect can be divided into – Voice interconnects – Signaling /Data interconnects

n

The MSCs voice/signaling interconnect may be designed to allow for alternate routing within the PLMN. If Route AB fails route AC to CB can succeed

MSC/VLR B

MSC/VLR C GMSC/VLR A

498

MSC MSC signaling signaling Interconnects Interconnects n

The MSC SS7 signaling interconnects can be planned using an STP pair (a separate hardware) or one of the MSCs in the network can perform STP functionality (if supported by the switch manufacturer).

MSC/VLR B

MSC/VLR C GMSC/VLR STP

National SS7 network

499

MSC MSC Planning Planning Considerations Considerations n

n

n

For a small network (< 3 MSCs) it is recommended to configure the MSC to perform STP functions. As the network expands it may be feasible to plan for local STP pairs which can then connect to the national STP network. Some of the important factors in deciding the need are: – Complexity of the network » Too many voice and signaling interconnect through the MSC

– Maintainability » As the network becomes larger it may be harder to maintain, so it is better to separate the packet switching from the circuit switching functions.

500

NSS NSS Configuration Configuration n

n

n

The operator may or may not, depending on the terms of its license, have the right to mesh its MSCs and GMSCs and have its own transit exchanges. Similarly, the operator may have the right to set up its own signaling links between NSS machines and have its own Signaling Transfer Points (STPs). In either case, operators must decide on the number and location of the GMSCs (e.g., in the same machine as an MSC or not), the interworking functions with the fixed networks and the SMS-GW for short messages etc. 501

Possible Possible SSS SSS configurations configurations n

The following shows an example of SSS star trunk configuration where A,B, C and D are gateways to their respective SSS network.

A C

B D 502

Tandem Tandem Switches Switches n

The system complexity and interconnect can be eliminated by adding Tandem switch which performs trunk routing functionality (E an F can perform tandem switch functionality in addition to other functionality)

A C E B

F D 503

NSS NSS Configuration Configuration (Cont.) (Cont.) n

n

A daisy chain configuration may be effective for small network with a few interconnects (up to 4). It is recommended when expanding such a network a Tandem switch with trunk routing capabilities be added, so that the daisy chain configuration will be changed to a star interconnect configuration.

a

a d

b c

c d

b c

504

GMSC, GMSC, HLR, HLR, IWF IWF n

n n

n

Select one centralized location for GMSC, this location should have easy/low cost access to public networks, such as PSTN, ISDN, PSPDN,.. Usually IWF is co-located with GMSC. To ensure the availability of HLR, at least two HLRs are usually planned. One HLR can be co-located with GMSC and the other HLR at a different location preferably co-located with one of other MSC’s. 505

GMSC GMSC Connections Connections (option (option 1) 1)

P S T N MSC GMSC MSC

HLR

P S T N

506

GMSC GMSC Connection Connection (option (option 2) 2)

P S T N MSC SS7 Packet Switch Network

MSC

GMSC HLR

P S T N

507

HLR/AC planning n

n

n

n

The HLR/AC can be part of the MSC or in a distributed architecture a separate platform. With in the IN architecture the HLR is an SCP (Service Control Point) which will perform service definition/execution environment. The HLR/AC must be planned as a pair to avoid single point of the failure. Generally the operator’s network can be supported by a pair of HLR/AC supporting multiple MSCs. Choose the fastest/relatively economical hardware platform since the computer technology is at high gear. Chose an HLR platform that is expandable. 508

HLR/AC HLR/AC n

Plan for the HLR/AC to be on a separate platform than the switch. – Allows for easier introduction of services when integrated with the SCP. – Since it is based on computer platforms/and not a switching platform, it will be » Easier to maintain/upgrade » Easier to expand » More cost effective in the long run » Faster processing power and more capacity (memory) in short time. 509

EIR EIR n

n

Initially plan to include the EIR in the HLR or MSC depending on the configuration supported by the manufacturer. As the network grows follow the distributed architecture

510

Chapter Chapter 5. 5. n

n n

Fixed Network Configurations Rules/ Planning Options Network Expansion for Existing System Trends in GSM Networks and Future Mobile Networks – UMTS and IMT2000 Perspectives

n

Course Summary and Discussions

511

Planning Planning Exiting Exiting Network Network The purpose of the planning for existing network is usually – System improvement » To expand the system » To introduce new elements to the network » To increase system reliability » To add new features/services

– System Problem identification and resolution

512

Approach Approach n

n

After determining the objective and purpose of planning Perform the following steps as required by the objective before any new services or additional growth can be planned. – Functional Model – Traffic Flow (only when adding new service or new elements) – Data collection – Cost analysis 513

Approach Approach n

Functional Model – A network block diagram defining the interfaces » Signaling interfaces » Voice Trunk interconnects » Number Routing and address routing information

n

Traffic Flow (only when adding new service or new elements)

514

Approach Approach (cont.) (cont.) n

Data collection – For a fix period of time (i.e 10 days) collect statistical data from each network element that is effected by the objective. The statistical data normally is collected by the by the OMC. For specific data sometimes it is required to execute a batch file on the OMC or on the specific network element. – Data Analysis – Analyze the data collected to meet the objective.

n

Cost analysis – Perform the transport network cost analysis – Physical space cost analysis – Equipment life cycle analysis v.s cost 515

Traffic Traffic Flows Flows n

n

When adding a new service/subscriber feature or a new network element to the network the effect of the change must be identified. Obtain the message flow diagram showing all the elements involved, including – – – – –

n

The number of messages The size of each message % of subscribers expected to use the service/feature Estimate the number of transaction/sec Estimate Call mix, traffic model and service mix model impact

These information will be required later to identify whether or not the current system can support the feature. 516

Data Data Collection Collection n

n

Collect the data from each network element that is affected, on an hourly basis (Some network elements have the flexibility to present the data in many forms e.g. plots, charts etc.) Collect the information required from the MSC/VLR and the HLR to construct – – – –

The Call Mix The Traffic model The service mix model Collect the processor utilization usage. » » » »

Collect Call attempts /hr from the MSC/VLR Collect number of Transactions /hr from the HLR or VLR Plot the MSC processor utilization v.s Call attempts /hr Plot the HLR or VLR processor utilization v.s number of transactions/hr

517

Data Data Collection Collection n

Signaling links statistical data from each data link that is to be effected. Specifically the – – – – – –

Number of frame rejects/hr Number of frame retries/hr Number of signaling information frames/hr Total number of messages /hr Total number of bytes/hr Obtain the link utilization for the element » total number of bytes per hr * 8 / 3600 / maximum link speed

n

Voice trunk utilization – Obtain the voice trunk utilization from the BSC or the MSC 518

Processes Processes Within Within aa Network Network Element Element n

Note: Each fixed network elements processor can perform anyone or all of the following functions, therefore it is very important when collecting/analyzing the data to know how each processor is used DATABASE

I/O Communications (Data link)

APPLICATION Call processing, Mobility

ADMINISTRATION, O&M (Billing, User Interaction)

519

Data Data Analysis Analysis (Call (Call mix) mix) n

From the Call mix, Traffic model and Service model – Compare the Call mix model obtained to the model initially used to plan the network if the call mix ratios varies more than a few % an overall system data collection/analysis is required. Otherwise no action is required from the call mix. – Compare the traffic model data obtained to the model initially used to plan the network if the BHCA or no of HO has increased (%25)and the system experiencing unexplained problems perform an overall system data collection/analysis. Otherwise no action is required. – Compare the service model data obtained to the model initially used to plan the network if the ratio of service usage has increased more than 25% identify the the elements/signaling links that are effected by the service. Perform data collections and analysis of the element(s). 520

Data Data Analysis Analysis (Processors) (Processors) n

From the MSC processor utilization v.s Call attempts /hr plot – If the Processor utilization exceed the planning limit (recommend 75 to 80%) for a the Maximum BHCA supported and if this condition consistently (more than once) occurs for a given period (i.e 10 days) then a » A Processor upgrade or » A system expansion or » A system rerouting /reconfiguration is required.

– Otherwise if the Processor utilization is not reaching the planning limits use the data to estimate capacity limits for future growth. Share the data with customer/marketing. 521

100

Processor Processor utilization utilization

Day 2 Day 1

Porcesor 20

40

60

80

The Planning Limit

1000

2000

3000

4000

5000

Call attempts /hr

522

Data Data Analysis Analysis (signaling (signaling link) link) n

From the data link utilization % – If this is an SS7 link and link utilization for each link in the link set is over 40% consider adding another link. – Forecast system growth/ additional traffic can be supported – Note: When adding a new service/element the traffic impact must be added to the collected data.

n

From excessive number of frames rejects & retries – Can detect possible physical layer problems – Processors over load and possible bottlenecks » Rejects >= Retries > 5% Physical Link has problem » Retry- Reject > 1% Processor is overloaded 523

Data Data Analysis Analysis (Voice (Voice Trunks) Trunks) n

Voice Trunk utilization – One can estimate the voice link utilization by: – Observing the busy/idle status of each time slot (e.g. in the E1 link) – Compute the percentage of busy cases for each time slot over a period of time, e.g. 10 days. – Average over all time slots to obtain the overall link utilization.

n

If utilization is above the target need to add links, why?

# busy / #Total 524

Data Data Analysis: Analysis: Service Service Availability Availability n

Service Availability data can help identify – System problems /failures – Further data collection may be required on each element to identify the cause of system failures.

n

Service Availability – Collect each network elements availability and use the following rules to calculate the service/system availability » % of the time the service is available for a given period.

n

Plot the result of service availability v.s hr 525

Example Example :MSC/VLR :MSC/VLR processes processes n

Call Processing(CP) and Mobility management processors can be monitored for their utilization. A Plot of the BHCA v.s CP processor utilization % or call/sec v.s processor load can determine – The need for CP processor expansion or upgrade

The new Services effect on the processors n I/O and communications processors can be monitored for its utilization. A plot of no of messages/sec v.s the I/O processor utilization % can determine – The need for I/O processor expansion or upgrade

The links statistics can be monitored for no of messages/sec to determine link overload. Statistics collected based on % of frame retries should lead to identifying network problems. 526

Example: Auc Example: HLR/ HLR/Auc n

Collect hourly statistics data base on the following transactions. Determine average hourly transactions. – Authentication – Location Updates – Terminations

n

n n

Collect hourly data on processor utilization. Determine average hourly utilization Plot no of transactions/hr v.s processor utilization Identify bottlenecks. I/O, application or database

527

Exercise Exercise

528

Chapter Chapter 5. 5. n

n n

Fixed Network Configurations Rules/ Planning Options Network Expansion for Existing System Trends in GSM Networks and Future Mobile Networks – UMTS and IMT2000 Perspectives

n

Course Summary and Discussions

529

ITU ITU and and IMT2000 IMT2000 n

n

n

n

Studies in the International Telecommunications Union’s Radio-communication Sector (ITU-R) on Future Public Land Mobile Telecommunication Systems (FPLMTS), are aimed at providing mobile telecommunications Anywhere - Anytime. These studies are intended to develop systems that could be used around the year 2000 and will operate in a frequency band around 2000 MHz. A new name has been proposed because FPLMTS is difficult to pronounce in any of the ITU languages! The proposed new name is International Mobile Telecommunications - 2000 (IMT-2000). 530

IMT2000 IMT2000 (Cont.) (Cont.) n

n

n

IMT-2000 are third generation systems which aim to unify the diverse systems we see today into a radio infrastructure capable of offering a wide range of services around the year 2000 in many different operating environments. A number of different radio environments are involved covering very small indoor cells with high capacity all the way through large outdoor terrestrial cells to satellite coverage. A major focus is to maximize the commonality between the various radio interfaces involved in order to simplify the task of building multi-mode mobile terminals covering more than one operating environment. 531

IMT2000 IMT2000 (cont.) (cont.) n

n

Initial studies were aimed at defining the objectives for FPLMTS and the resulting spectrum requirements as part of the ITU-R (ex-CCIR) input to the World Administrative Radio Conference in February 1992 (WARC-92). WARC-92 identified the bands – 1885 - 2025 MHz and – 2110 - 2200 MHz,

n n

on a global basis for FPLMTS This includes the bands 1980 - 2 010 and 2170 - 2200 MHz for the satellite component of FPLMTS.

532

IMT2000 IMT2000 & & Developing Developing Countries Countries n

n

An important part of the ITU-R studies on FPLMTS/IMT-2000 is the potential for these new mobile radio technologies to provide cost effective and flexible access to the global telecommunications networks in developing countries and underdeveloped parts of developed countries. The close relationship between the satellite and terrestrial components of FPLMTS/IMT-2000 enables the deployment of service via satellite initially, where there is little or no existing fixed infrastructure with the conversion to terrestrial infrastructure in areas as development conditions permit. 533

Next Next Generation Generation PCS PCS 200 KHz GSM Evolution Including EDGE Harmonization

ETSI SMG2

FMA1

ITU-R

FMA2

ARIB

TIA

FRAMES

534

ETSI ETSI and and 3G 3G Radio Radio Interface Interface n

n

On 28-29 January 1998 in Paris, France, an agreement was reached by consensus on the radio interface for third generation mobile system, UMTS (Universal Mobile Telecommunications System). The solution, called UTRA, draws on both W-CDMA and TD-CDMA technologies. The Solution is as follows: – In the paired band (FDD - Frequency Division Duplex) of UMTS the system adopts the radio access technique formerly proposed by the WCDMA group. – In the unpaired band (TDD - Time Division Duplex) the UMTS system adopts the radio access technique proposed formerly by the TD-CDMA group.

535

Objectives Objectives n

Following objectives have to be achieved through the process of selecting parameter of FDD/TDD mode – – – –

Low Cost Terminal Harmonization with GSM FDD/TDD dual mode operation Fit into 2*5MHz spectrum allocation

536

Supporters Supporters n

The parties that made the proposal leading to this new solution included – Alcatel, Bosch, Ericsson, Fujitsu, Italtel, Matsushita (Panasonic), Mitsubishi Electric, Motorola, NEC, Nokia, Nortel,Siemens and Sony as well as Analog Devices, Cegetel, Cellnet, CSEM/Pro Telecom, Deutsche Telekom, France Telecom, Mannesman Mobilfunk, NTT DoCoMo, Samsung Electronics, SFR, T-Mobil, Telecom Finland, Telia, TexasInstruments, TIM and Vodafone.

n

n

NTT DoCoMo, the leading Japanese cellular network operator, participated in the meeting as an observer, welcomed the solution reached and expressed full support. The agreed solution offers a competitive continuation for GSM evolution to UMTS and will position UMTS as a leading member of the IMT-2000 family of systems recommendations being developed in the ITU 537

Enhanced Enhanced Data Data GSM GSM Evolution Evolution EDGE System Level Description n EDGE uses the same 8 Time Slot / 200KHz channelization in GSM, but uses a different modulation than GMSK. n This modulation is called Quarternary Offset QAM or Binary Offset QAM, which provides higher spectral efficiency than GMSK. n Using Q-OQAM and time slot aggregation, EDGE claims to support high speed data upto 384kbps over 200khz channel. 538

EDGE EDGE (cont.) (cont.) n

n

n

Channel Reuse: EDGE claims to be able to use a 1/3 (cells/sector) reuse factor. This reuse factor is claimed to be feasible even with fixed channel assignment. Another system aspect of EDGE is its rate adaptation, meaning selecting the best combination of coding and modulation to meet the Eb/No at maximum throughput or user data rate. The rate adaptation relies on the mobile and base stations measurements of the channel under bursty interference/fading conditions. 539

EDGE: EDGE: Pedestrian Pedestrian Environment Environment n

n n

n n n n

For Microcells with pedestrian mobile speeds of up to 10 km/hr the following is proposed: Carrier Spacing 200 kHz Modulation Quaternary-Offset-QAM, BinaryOffset-QAM Time Slot duration 576.92 µ sec Time Slots 8 Gross Carrier rate Up to 521.6 kbps User Data Rate >384 kbps with 8 time slots 540

EDGE: EDGE: Low Low Speed Speed Vehicular Vehicular Env Env.. n

n n n

n n n n

For Macrocells with vehicular mobile speeds of up to 100 km/hr the following is proposed: Carrier Spacing 200 kHz Modulation Quaternary-Offset-QAM, BinaryOffset-QAM, GMSK Time Slot duration 576.92 µ sec Time Slots 8 Gross Carrier rate Up to 521.6 kbps User Data Rate >384 kbps with 8 time slots 541

EDGE: EDGE: High High Speed Speed Vehicular Vehicular Env Env.. n

n n n n n n

For Macrocells with vehicular mobile speeds of from 100 km/hr to 500 km/hr the following is proposed: Carrier Spacing 200 kHz Modulation Binary-Offset-QAM, GMSK Time Slot duration 576.92 µ sec Time Slots 8 User Data Rate >144 kbps with 8 time slots

542

EDGE: EDGE: Indoor Indoor Office Office n

n n n n n n

For Picocells with mobile speeds of 0 km/hr the following is proposed: Carrier Spacing 200 kHz Modulation Quaternary-Offset-QAM Time Slot duration 576.92 µ sec Time Slots 8 Gross Carrier rate 521.6 kbps User Data Rate >1920 kbps with 5 aggregated carriers each with 8 time slots

543

FYI: FYI: IN IN and and GSM GSM n

n

n n

Intelligent Network is a technology that allows the rapid introduction of the new features/services within a network (wireless or wire-line) The technology is base on a distributed network which offloads the traditional switching platform from performing service creation and feature development. Perform service creation function on computing platforms. Allows inter-working between different standards. The backbone is based on SS7. 544

Current Current IN IN Architecture Architecture

IP

IN CS1

SMS SMP

SCP

SCE

IP

IN CS1 IP HLR SSF

SSF MAP MSC

MAP

MSC 545

IN IN /CAMEL /CAMEL Architecture Architecture n

n

Customized Application for Mobile Enhanced Logic (CAMEL) is a GSM standard that addresses IN. (GSM 01.78,02.78,03.78,04.78) ITU-T Q1224 recommendation for IN CS-2 (Capability Set 2) describes Functional Entities (FE). ACF Authentication Control function CCF Call Control Function LRF Location Registration Function RACF Radio Access Control Function RCF Radio Control Function RTFRadio Terminal Function SCEF Service Creation Environment function SCF Service Control Function SDF Service Data Function SMAF Service Management Access Function SMF Service Management Function SRF Specialized Resource Function SSF Service Switching Function

546

GSM GSM and and IN IN Mapping Mapping IP SRF

MS RTF

AC ACF

SCP SCF SDF

SN SCF SDF SRF

PSTN ISDN PSPDN

MSC/VLR BSS RCF

CCF SSF

HLR

RACF LRF SRF ACF

CCF

LRF SCF SDF 547

IN IN n

n

n

n

Call models and triggers are the functional bases for Call processing (CCF) in IN. The call models are the states machines. – Origination Call Model – Termination Call Model – Registration Call Model Triggers are the events that suspends the call processing. (when an * is detected suspend processing and send a message to the HLR) Origination triggers Termination Triggers • • • •

All Calls 0-15 digits Feature codes specific

No Answer Busy No page response

548

IN IN (cont.) (cont.) n

Within a call model there are – Point in Call (PICs) Null , Collect information, select_Facility analyze information etc.) – Detection Point (DPs) Origination attempt, origination attempt authorized etc..

Note: example of termination call model (this is not a complete call model), T_Null

T_exception Termination_Attempt DP

T_abandon DP

Authorize_termination-attempt Termination_Attempt_Authorized DP Select_Facility T_Busy DP No triggers are defined for these DP

549

Future Future n n

n

n

n

Alignment with Fixed network e.g CS2/CS3 Exploiting the mobile capabilities available in GSM Capabilities for GSM/IN/Internet convergence versus the traditional IN GSM and CAMEL -core for next generation systems UMTS switching Future services, – Virtual Private Networks – Call Screening Applications – Location dependent services 550

Chapter Chapter 5: 5: Review Review and and Discussions Discussions

Configuration Rules Planning Existing System Next Generation Systems

551

Course Course Summary Summary GSM Protocol Chennelization & Network Elements

Signaling Protocols & Interfaces

Fixed Network Planning

Traffic Theory

Network Dimensioning

552

References References

n

n

n

n

n n

“An Introduction to GSM”, Siegmund M. Redl, Matthias K. Weber and Malcolm W. Oliphant, Artech House Publishers, 1995 “The GSM System for Mobile Communications”, Michel Mouly and Marie B. Pautet, 1995 “GSM System Engineering”, Asha Mehrotra, Artech House Publishers, 1997. “Wireless Communications, Principles and Practice”, Theoddore Rappaport, Prentice Hall/IEEE Press 1996. IEEE Communications Magazine IEEE Personal Communications Magazine 553

Congratulations!!! Congratulations!!!

554