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GB_BT01_E1_1 GSM Basics

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

Others

1G

Analog

GSM

CDMAIS95

TDMAIS-136

PDC

2G

Digital

Market

Driving

3G

IMT-2000

UMTS

WCDMA

CDMA

2000

Market

Driving

TD-SCDMA

Mobile Telecommunication Technology

Evolution

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GSM History

1989GSM Standard Take effect

1

1991GSM system launched commercially

2

1994GSM enter into China

3

2000China Mobile

400 million subscribers

4

Custome

r

Demand

Competition

Technology

Development

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Development of mobile communication system

1 k

1 M

2 M

Bit/s

Messaging

SMS

Voice

Graphics

text

Medium

quality

High

quality

Mobile Office

VideoUMTSUMTS

GPRSGPRS

2002

2000

GSMGSM10 k

1999 56 k

EDGEEDGE 2001

115 k

384 k

Alwa

ys-on

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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 Field 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 architecture

BTS

BSC

MSC

VLR HLR AuC EIR

PSTN,ISDN...

OMCOMC

NMCX.25 links

GSM interfaces

Voicemail Server

SM-SC

MS (Mobile Station)

BSS (Base Station System)

NSS(Network Switching

Subsystem)

OMS(Operations & MaintenanceManagement)

MS

http://www.nokia-asia.com/nokia/0,,48192,00.html

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GSM network entities

MS (Mobile Station)Mobile Equipment

Subscriber Identity Module (SIM)

BTS (Base Transceiver Station)Provide radio channels

BSC (Base Station Controller)

Radio resource management

Transcoder

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GSM network entities

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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GSM network entities

MSC (Mobile service Switching center)Circuit switching

AUC (Authenticate Center) :

Authenticate subscriber access

EIR (mobile station Equipment Identity Register) :

Identify terminal equipment

OMC (Operation and Maintenance Center)Provide MMI to control and monitor system

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GSM interfaces

MS BTS BSC MSC

VLR VLR

HLR

MSCEIR

Sm

Um

Abis A B

D

C

E F

G

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GSM operation band

SYSTEM P-GSM 900 E-GSM 900 GSM 1800 GSM 1900

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 radio frequency channel Number

ARFCN

GSM900 Fu (n) = 890 + 0.2n MHz

Fd (n) = Fu(n) + 45 MHz01n 124

GSM1800

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

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

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Multiple Access Technology (MAT)

Many subscribers share commontelecommunication lines without interference to

each other.

M T

GSM

FDMA

TDMA

CDMA

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FDMA

FDMA Identify by frequency

Time

Frequency

FDMA

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TDMA

TDMA Identify by time

Time

Frequency

TDMA

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CDMA

CDMA Identify by code

Time

Frequency

CDMA

Code

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Content

GSM System Overview GSM Common Events

Basic Calling Process

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Subscriber status

IMSI Attach

IMSI Detach

MS busy

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Location Update

Originated by MS Location info stored in

SIM

MS monitor system

infooriginatelocation update once

the new LAC is

different from that in

SIM

HLR

VLR

MSC (old)

VLR

MSC (new)

LocationUpdate

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Location Update

Type Power on

IMSI ATTACH/DETACH

Location register

MS power on/off Normal location update

MS change LA

Periodic location update

Operator decide the period(timer)

Location update when time

out

V L RM S C

LA 2LA 1

ON

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Handover

Handover: Hand-over is a process that transfers a MS thatis in setting up or busy status to a new traffic channel

Why need handover

Keep and save the call in progress

Improve network service quality

Decrease call drop rate

Decrease congestion rate

Who will be involved

MSBTSBSCMSC

MSmeasure downlink radio signal level BTSmeasure uplink radio signal level and quality and send the

results to BSC

BSCevaluate and decision of HO

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

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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

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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 thecontrol channel.

MS change its service

cell in IDLE state

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Authentication and Encryption

Triplet RAND: the question asked by the network side

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

confidential way

SRES: signed response. It is obtained through thecalculation of subscribers unique key parameter Ki.

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Authentication process

Execute authentication when MS registersetup calllocation update and

active/deactivate supplementary service

It is optional

A3 algorithm Mobile Terminal Network

A3 algorithm

Random number generatorKi RAND

SRES'

SRES

Ki

A3 algorithm

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Encryption process

Kc: Encryption key 64-bits (A8 algorithm) A5 algorithm (exclusive or)

It is optional.

Mobile Terminal Network

A8 algorithm

Random number

generatorKiRAND

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)

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Content

GSM System Overview GSM Common Events

Basic Call ing Process

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Initialization

Initialization is a random access process

Ch request (RACH)

TA, access reason

ACTSDCCH

Imm Assign SDCCHAGCH

Initial messageSDCCH

Imm Assign SDCCHAGCH

ACT ACKSDCCH

MS BTS BSC

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Location update process

(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 from 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 from 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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