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GBC_001_E1_1 GSM Basic

ZTE University

GSM-BSS Team

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Objective

At the end of this course, you will be able to:

Understand GSM system architecture

and function

State GSM common events

Describe basic calling process

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Content

GSM System Overview

GSM Common Events

Basic Calling Process

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AMPS

TACS

NMT

Other s

1G

Analog

GSM

CDMA IS95

TDMAIS-136

PDC

2G

Digital

Market

Dr iving

3G

IMT-2000

UMTS

WCDMA

CDMA

2000

Market

Dr iving

TD-

SCDMA

Mobile Telecommunication Technology Evolution

GSM System Over view

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GSM Histor y

1989GSM Standard Take effect

1

1991GSM system launched commercially

2

1994GSM enter into China

3

2000China Mobile

400 million subscribers

4

Custome

r

Demand

Competitio

n

Technology

Development


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Development of mobile communication system

1k

1 M

2 M

Bit/s

Messaging

SMS

Voice

Gr aphics

text

Medium

quality

High

quality

Mobile Office

VideoUMTSUMTS

GPRSGPRS

2002

2000

GSMGSM10k

1999 56k

EDGEEDGE 2001

115k

384k

Always-o

n


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The way to 3G


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Meaning of GSM

GSM: Group Special Mobile

GSM: Global System for Mobile


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GSM specification

Field 1: General

Field 2: Services

Field 3: Network Functions

Field 4: MS-BS Interfaces and Protocols

Field 5: Physical Layer on Radio Path

Field 6: Speech Coding


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GSM specification

Field 7: MS Terminal Adaptor

F

ield 8: BS-MSC Interface

Field 9: Network Inter-working

Field 10: Service Inter-working

Field 11: Equipment and Model Acceptance Specification

Field 12: Operation and Maintenance


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GSM Network development

1982: The group special mobile

1986: On-site test

1987: TDMA, RPE-LTP, GMSK

1988: MOU

1989: GSM took effect

1991: First GSM network was deployed

1992: GSM standard was frozen

1993: GSM phase 2 complete

1994: GSM phase 2+ for mobile data service


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GSM system ar chitecture

BTS

BSC

MSC

VLR HLR AuC EIR

PSTN,ISDN...

OMCOMC

NMCX.25 links

GSM inter faces

Voicemail Ser ver

SM-SC

MS (Mobile Station)

BSS (Base Station System)

NSS(Network Switching

Subsystem)

OMS(Operations & MaintenanceManagement)

MS


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GSM network entities

MS (Mobile Station)

Mobile Equipment

Subscriber Identity Module (SIM)

BTS (Base Tr ansceiver Station)

Provide radio channels

BSC (Base Station Contr oller )Radio resource management

Transcoder


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HLR (Home Location Register )

Database

Subscriber data

Subscriber location info.

VLR (Visitor Location Register )

Database

MSRN (Mobile Station Roaming Number)

TMSI (Temporary Mobile Subscriber Identification)

Location area codeLAC

Subscriber data related to supplementary service


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MSC (Mobile ser vice Switching center )

Circuit switching

AUC (Authenticate Center ) :

Authenticate subscriber access

EIR (mobile station Equipment Identity Register ) :

Identify terminal equipment

OMC (Oper ation and Maintenance Center )

Provide MMI to control and monitor system


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GSM ser vice area

GSM Ser vice Area

PLMN Ser vice Area

MSC Ser vice Area

LocationArea

Cell


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GSM inter faces

MS BTS BSC MSC

VLR VLR

HLR

MSC

EIR

Sm

Um

Abis A B

D

C

E F

G


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GSM oper ation band

SYS M GSM GSM GSM GSM

Frequencies

- Uplink- Downlink

890 - 915 MHz935 - 960 MHz

880 - 915 MHz925 - 960 MHz

1710 - 1785 MHz1805 - 1880 MHz

1850 - 1910 MHz1930 - 1990 MHz

Wavelength ~33 cm ~33 cm ~17 cm ~16 cm

Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz

Duplex Distance 45 MHz 45 MHz 95 MHz 80 MHz

Carrier Separation 200 kHz 200 kHz 200 kHz 200 kHz

Radio Channels 125 175 375 300


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Absolute r adio f requency channel Number ARFCN

GSM900

f Fu (n) = 890 + 0.2vn MHz

f Fd (n) = Fu(n) + 45 MHz01e n e 124

GSM1800

f Fu (n) = 1710.2 + 0.2v(n-512) MHz

f Fd (n) = Fu(n) + 95 MHz512 e n e 885


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Multiple Access Technology (MAT)

Many subscribers share common telecommunication

lines without interference to each other.

MAT

GSM

FDMA

TDMA

CDMA


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FDMA

FDMA

f Identify by f requency

Time

Frequency

FDMA


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TDMA

TDMA

f Identify by time

Time

Frequency

TDMA


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CDMA

CDMA

f Identify by code

Time

Frequency

CDMA

Code


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Content

GSM System Overview

GSM Common Events


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Subscr iber status

IMSI Attach

IMSI Detach

MS busy

GSM Common Events

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Location Update

Originated by MS

Location info stored in

SIM

MS monitor system info

originate location update

once the new LAC is

different from that in SIM

HLR

VLR

MSC (old)

VLR

MSC (new)

LocationUpdate

GSM Common Events

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Location Update

Type

f Power on

IMSI ATTACH/DETACH

Location register

MS power on/off

f Nor mal location update

MS change LA

f Per iodic location updateOper ator decide the

per iod (timer )

Location update when

time out

VLR MSC

LA 2LA 1

ON

GSM Common Events

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Handover

Why need handover

f Keep and save the call in progress

f Improve network service quality

Decrease call drop rate

Decrease congestion rate

Who will be involved

f MSBTSBSCMSC

MSmeasure downlink radio signal level

BTSmeasure uplink radio signal level and quality and send the

results to BSC

BSCevaluate and decision of HO

MSC routes the call to the other MSC during Inter-MSC HO

Handover : Hand-over is a process that transfers a MS that is in setting

up or busy status to a new traffic channel

GSM Common Events

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Handover classification

Reason:

PBGT

Signal level

Signal quality

Distance

Traffic

TA:

Synchronous

Asynchronous

Position:

Intra-cell

Inter-cell

Intra-BSC

Inter-BSC

Inter-MSC

GSM Common Events

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Cell selection and Reselection

After a MS is turned on, it will attempt to contact

a common GSM PLMN, so the MS will select an

appropriate cell, and extract from it the

parameters of the control channel.

MS change its service cell in

³IDLE´ state

GSM Common Events

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Authentication and Encr yption

Triplet

f RAND: the question asked by the network side

f Ki: stored in the SIM card and AUC in a very confidential

way

f SRES: signed response. It is obtained through the

calculation of subscriber¶s unique key parameter Ki.

GSM Common Events

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Authentication pr ocess

Execute authentication when

fMS register setup calllocation update and active/deactivate

supplementary service

f It is optional

f A3 algorithm

Mobile Terminal Network

A3 algorithm

Random number generator Ki RAND

SRES'

SRES

Ki

A3 algorithm

GSM Common Events

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Encr yption pr ocess

Kc: Encryption key 64-bits (A8 algorithm)

A5 algorithm (exclusive or)

It is optional.

Mobile Terminal Network

A8 algorithm

Random number

generator KiRAND

Kc

Ki

Kc

A8 algorithm

A5

Frame No.

(22-bit)Kc (64-bit)

A5

S1

(114-bit)

S2 S1 S2

MS BTS

Frame No.

(22-bit)Kc (64-bit)

(114-bit) (114-bit) (114-bit)

GSM Common Events

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Content

GSM System Overview

GSM Common Events


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Initialization

Initialization is a random access process

Basic calling pr ocess

Ch request (R ACH)TA, access reason

ACTSDCCH

Imm Assign SDCCHAGCH

Initial messageSDCCH

Imm Assign SDCCHAGCH

ACT ACK SDCCH

MSBTS BSC

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Location update pr ocess

(1) MS moves from one BTS to another BTS

(2) Learn to the broadcasting information

(3)(4) MS sends the LU request to MSC-A.

(5) MSC-A sends the LU message to HLR

(6) HLR sends back subscriber data.

(7)(8) Subscriber data registration in the VLR.

(9) Sending LU response message

(10

) Notifying the original VLR to delete subscriber data.


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Outgoing call f r om MS to PSTN

(1) Random access channel.

(2) Set up signaling connection between

MS and MSC.

(3) Authentication and encryption and

enter the call setup starting phase.

(4) Service channel allocation

(5) Send ringing to the called subscriber,

and send back the call connection

acknowledgment signal to MS.

(6)The called subscriber offhooks to reply,

in which case a response (connection)

message is sent to MS, thus entering the

ultimate call session phase.


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Incoming call f r om PSTN to MS

(1) Send MSISDN number to GMSC

(2) Requests HLR for the MSC address

(3) HLR requests VLR to assign MSRN

(4) GMSC re-search for routes to set up

connection to the visited MSC by MSRN.

(5)(6) MSC obtains related subscriber data

(7)(8) MSC sends paging messages

(9)(10) The MS sends back the paging

response messages, then carries out the

same steps of (1), (2), (3), (4) as shown in the

above outgoing call flow till the mobile station

rings.

(11) The mobile subscriber offhooks to answer,

thus the response (connection) message is

sent back to the fixed network


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MS to MS call

(1) MS1 dials the phone number of MS2. BSS informs MSC1 of the call.

(2) MSC1 analyzes the phone number of MS2, finds out the HLR of MS2 and sends the route

application to HLR.

(3) HLR queries the current location information of MS2 and obtains MSRN from the MSC2/VLR2.(4) MSC2/VLR2 allocates the route information, that is, MSRN and submits the MSRN to the HLR.

(5) HLR sends the MSRN to the MSC1.

(6) MSC2 sets up the call with MSC2 according to the MSRN.

(7) MSC2/VLR2 sends the paging message to MS2.

(8) MSC2/VLR2 receives the message, indicating the access of MS2 is allowed.

(9) The call between MSC2 and MSC1 is set up.

(10) MSC1 sends the successful connection signal to MS1. MS1 and MS2 can talk over the phone.


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