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G LOBALSYSTEM FORM OBILE COMMUNICATION

(GSM )

NETWORK ARCHITECTURE

V.G.SABUSUB DIVISIONAL ENGINEERREGIONAL TELECOM TRAINING CENTREBSNL, TRIVANDRUM

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GSM Specifications - I Frequency Bands

GSM 900 MhzGSM 1800 MHz

BTS

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GSM Specifications

GSM 900 MhzMobile to Cell(UP-LINK) -890 to 915 MHzCell to Mobile (DOWN -LINK) - 935 to 960 MHz

GSM 1800 MhzMobile to Cell(UP-LINK) -1710 to 1785 MHzCell to Mobile(DOWN -LINK) - 1805 to 1880 MHz

Channel Bandwidth - 200 KHzAccess Method - TDMA/FDMAModulation - GMSK

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GSM - MULTIPLE ACCESSGSM uses both FDMA & TDMA

Freq

Mhz.

890.2

0

890.4

1

890.6

2

890.8

3

891.0

4 5

915

123

FDMA Access along Freq. axis Each RF carrier 200khz apart

Total 124 RF Channels available.

One or more carrier assigned to each base station

...

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5

GSM FDMA(Frequency Division

Multiple Access)

25 MHz 25 MHz

Mobile to Base

0 1 2

890.2 890.4 890.6 (MHz)

Base to Mobile

0 1 2

935.2 935.4 935.6

200 kHz

45MHz

Channel layout and frequency bands of operation

890 935 960 915

200 kHz

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GSM (900Mhz)63,64,66,67,68,69,70,71,72,73,74,75,76,7

7,79,80,81,86,87,110,111,112,114,115,116,117,118119,121,122,123 (Total-31)

GSM(1800 Mhz)1775.0,.2,.4,.6,.8, 1776.0,.2,.4,.6 (Total-9)

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GSMTDMA

Typical TDMA/ FDMA frame structure

8765

43

21

8765

43

21

45 MHz

Frequency

F2 F1 (Cell transmit)

F2 F1(Cell Rx)

Amplitude

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GSM Specifications

Number of Channels - 124

Voice Channel Coding - RPE-LTP( 13 Kbps)

RPE-LTP - Regular Pulse Excitation Long Term Prediction

FULL RATE - 13Kb/s ; HALF RATE - 6.5 Kb/s

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GSMTypical GSM Architecture

MS

MS Mobile StationMSC Mobile Switching CentreBTS Base Transceiver StationBSC Base Station Controller

VLR Visited Location RegisterHLR Home Location Register

EIR Equipment Identity Register

AUC Authentication Centre

Data

HLR VLR

MSC

AUC

MSC

EIR

PSTN

PSPDN BTS

BSC

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NETWORK ARCHITECTURE

Air interface

MSC VLR SS#7

PSTNISDN

Data

Networks

SS#7

OSS

X.25

BTS

BTS

BSC

B

TS

MSC VLR

SS#7

A bis Interface A Interface

SS#7

HLR

GSM

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GSM Network Overview

ME

SIM

BTS

BTS

BSC

BSC

MSC

HLR

EIR

VLR

AuC

MobileStation Base Station Subsystem Network Switching

Subsystem

PSTNISDN

PSPDN

Um Abis

A

OMC

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Mobile StationMobile Station is really two distinct entities.

Mobile equipment or terminal.SIM Card.Mobile equipment, which is the actual Hardware, is

anonymous.

SIM card, implemented as a smart card holds thesubscriber information including a uniqueidentifier called International MobileSubscriber Identity (IMSI).

MS=ME+SIM

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SIM CARD

SIM provides personal mobility

SIM makes the terminal operational

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GSM Base Station Subsystem (BSS)

Base Station Subsystem (BSS) consists of

Base Station Controller (BSC)&

Base Transceiver Station (BTS)

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Base Station Subsystem(BSS)

BSS connects the MS and the NSS.Composed of two parts:The Base Transceiver Station (BTS) also called

Base Station.Base Station Controller (BSC).

BTS and BSC communicate across thestandardised Abis interface..

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GSM Base Transceiver Station (BTS)

BTS accommodates all radio transmission equipmentfor one antenna site along with the necessarymonitoring equipment.

One BTS can support several Trans-Receive Units

(TRX).

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Base Station Controller(BSC)

BSC manages the radio resources for one ora group of BTSs.

Handles radio-channel setup, handovers,and control of the RF power levels.

Establishes connection between the mobilestation and the MSC..

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GSM Base Station Controller (BSC)

BSC is connected via interfaces to MSC, OMCand BTS.

Its duties are

-Radio Channel Management-Sending fault alarms to OMC.-Handling of handover of a mobile station

changing a radio cell-Connectivity to BTSs..

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Network & Switching Subsystem(NSS)

Manages the communication between themobile users and other users.Provides all the functionality needed to

handle a mobile subscriber such as:Registration

Authentication

Handovers andRouting to roaming subscribers.

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Network & Switching Subsystem

Central component is the MSC (MobileServices Switching Centre). It performsthe switching functions of the network.

Gateway Mobile Services Switching Centreinterfaces between the mobile network and

PSTN..

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Network & Switching Subsystem

Mobile Switching Center (MSC) provides the services in conjunction withfour intelligent databases.

Home Location Register (HLR)Visitor Location Register (VLR)

Equipment Identity Register (EIR)Authentication Centre (AuC)..

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GSM Home Location Register

Contains all administrative information ofeach subscriber registered in an GSMnetwork.

Logically there is one HLR per GSMnetwork.

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Visitor Location Register.

VLR Contains selected administrativeinformation from HLR needed for call

control and provision of subscribed servicesfor each mobile located in the geographicalarea controlled by it .

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GSM Authentication Centre

-Used for security purposes.-Subscriber authentication data

ie.Authentication Keys Ki-Encryption data.

The authentication center (AuC) stores the

keys required for checking whether a mobilesubscriber is authorized to access the PLMN.

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GSM Equipment Identity Register..

The equipment identity register (EIR)contains a database consisting of threelists classifying the international mobile

equipment identities (IMEI) of allmobile equipment in the GSM network.

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GSM Equipment Identity Register

The white list contains all approved mobileequipment. The grey list contains suspiciousmobile equipment which needs observation. The

black list contains all mobile equipment which isnot allowed in the network.

The three lists are interrogated to determine

the status of the mobile equipment: whitelisted, grey listed, black listed.

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GSM Voice EncodingIn the case of full rate encoding, 8 voice

circuits are provided whereas in half rateencoding 16 voice circuits are possible.

-Voice encoding at 13 kbps

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GSM Digital Voice Transmission-I

-The voice signal is initially converted to a 13 kbps bit stream by a voice encoding process i.e. RegularPulse Excited- Long Term Prediction (RPE-LTP).

-To improve the voice immunity of the information

to be transmitted, the channel coding provides dataerror control with which the transmittedinformation can be reconstructed at the receivereven if the transmission path is disturbed.Thisincreases the bit rate to 22.8 kbps

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GSM Speech to Radio waves

Speech Coding

Channel Coding

Interleaving

Burst formatting

Ciphering

Burst formatting

Deciphering

Analog

Modulation

200kHz BW

Speech Decoding

Analog

200kHz BW

Demodulation

De-interleaving

Channel Decoding

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GSM Network Structure

-GSM Service Area

-PLMN Service Area

-MSC Service Area-Location Area

-Cells

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GSM - NETWORK STRUCTURE

CELL

Location Area

MSC Area

PLMN Area

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Questions ?

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Question-1

What are the up-link &

down-link frequencies inGSM 900 Mhz Band?

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Answer

Up-Link -890 to 915 Mhz

Down-Link-935 to 960 Mhz

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Question-2

What are the main H/W entitiesin BSS?

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Answer

BSC

BTS

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Answer

A- interface

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Question-4

Which database stores the subscriber relateddata permanently?

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Answer

HLR

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Question-5

In EIR which list contains

IMEIs that are assigned tovalid MSs ?

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Answer

White List

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THANK YOU