GSM Basic

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

Content

GSM System Overview GSM Common Events Basic Calling Process

AMPS

TACS

NMT

Others

1G

Analog

GSM

CDMA IS95

TDMAIS-136

PDC

2G

Digital

Market Driving

3G

IMT-2000

UMTSWCDMA

CDMA2000

Market Driving

TD-SCDMA

Mobile Telecommunication Technology Evolution

GSM History

1989 ： GSM Standard Take effect

1

1991 ， GSM system launched commercially

2

1994 ， GSM enter into China

3

2000 ， China Mobile 400 million subscribers

4

Customer

Demand

Competition

Technology Development

Development of mobile communication system

1 k

1 M

2 M

Bit/s

MessagingSMS

Voice

Graphics

text

Medium quality

High quality

Mobile Office

VideoUMTSUMTS

GPRSGPRS

2002

2000

GSMGSM10 k

1999 56 k

EDGEEDGE 2001

115 k

384 k

The way to 3G

Meaning of GSM

GSM: Group Special Mobile

GSM: Global System for Mobile

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

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

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

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 & Maintenance Management)

MS

GSM network entities

MS (Mobile Station)：Mobile Equipment

Subscriber Identity Module (SIM)

MS (Mobile Station)：Mobile Equipment

Subscriber Identity Module (SIM)

BTS (Base Transceiver Station)：Provide radio channels

BSC (Base Station Controller)：Radio resource management

Transcoder

BTS (Base Transceiver Station)：Provide radio channels

BSC (Base Station Controller)：Radio resource management

Transcoder

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 code （ LAC ）Subscriber data related to supplementary service

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 code （ LAC ）Subscriber data related to supplementary service

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

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

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

GSM service area

GSM Service Area

PLMN Service Area

MSC Service Area

Location Area

Cell

GSM interfaces

MS BTS BSC MSC

VLR VLR

HLR

MSCEIR

Sm Um Abis A B

D

C

E F

G

GSM operation band

SYSTEM P-GSM 900 E-GSM 900 GSM 1800 GSM 1900Frequencies- 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 cmBandwidth 25 MHz 35 MHz 75 MHz 60 MHzDuplex Distance 45 MHz 45 MHz 95 MHz 80 MHzCarrier Separation 200 kHz 200 kHz 200 kHz 200 kHzRadio Channels 125 175 375 300

Absolute radio frequency channel Number （ ARFCN ） GSM900 ：

Fu (n) = 890 + 0.2n MHz Fd (n) = Fu(n) + 45 MHz ， 01 n 124

GSM1800 ： Fu (n) = 1710.2 + 0.2(n-512) MHz Fd (n) = Fu(n) + 95 MHz ， 512 n 885

Multiple Access Technology (MAT)

Many subscribers share common telecommunication lines without interference to each other.

MAT

GSM

FDMA

TDMA

CDMA

FDMA

FDMA ： Identify by frequency

Time

Frequency

FDMA

TDMA

TDMA ： Identify by time

Time

Frequency

TDMA

CDMA

CDMA ： Identify by code

Time

Frequency

CDMA

Code

Content

GSM System Overview GSM Common Events Basic Calling Process

Subscriber status

IMSI Attach

IMSI Detach

MS busy

Location Update

Originated by MS Location info store

d in SIMMS monitor system info ， originate location update once the new LAC is different from that in SIM

HLR

VLR

MSC (old)

VLR

MSC (new)

LocationUpdate

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

VLRMSC

LA 2LA 1

ON

Handover

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 ？ MS 、 BTS 、 BSC 、 MSC

MS ： measure downlink radio signal level BTS ： measure uplink radio signal level and quality and send the res

ults to BSC BSC ： evaluate 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

Handover classification

Reason:

PBGT

Signal level

Signal quality

Distance

Traffic

TA:

Synchronous

Asynchronous

Position:

Intra-cell

Inter-cell

Intra-BSC

Inter-BSC

Inter-MSC

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 “IDLE” state

Authentication and Encryption

Triplet ： RAND: the question asked by the network side Ki: stored in the SIM card and AUC in a very confidentia

l way SRES: signed response. It is obtained through the calcu

lation of subscriber’s unique key parameter Ki.

Authentication process

Execute authentication when MS register 、 setup call 、 location update and active/d

eactivate supplementary service It is optional A3 algorithm Mobile Terminal Network

A3 algorithm

Random number generatorKi RAND

SRES'SRES

Ki

A3 algorithm

Encryption process

Kc: Encryption key 64-bits (A8 algorithm) A5 algorithm (exclusive or) It is optional.

Mobile Terminal Network

A8 algorithm

Random numbergeneratorKi

RAND

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)

Content

GSM System Overview GSM Common Events Basic Calling Process

Initialization

Initialization is a random access process

Ch request (RACH)TA, access reason

ACT （ SDCCH ）

Imm Assign SDCCH （ AGCH ）

Initial message （ SDCCH ）

Imm Assign SDCCH （ AGCH ）

ACT ACK （ SDCCH ）

MS BTS BSC

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.

Outgoing call from MS to PSTN

(1) Random access channel.

(2) Set up signaling connection between

MS and MSC.

(3) Authentication and encryption and ent

er the call setup starting phase.

(4) Service channel allocation

(5) Send ringing to the called subscriber,

and send back the call connection ackno

wledgment signal to MS.

(6)The called subscriber offhooks to reply,

in which case a response (connection) m

essage is sent to MS, thus entering the ul

timate call session phase.

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 conn

ection 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 respo

nse messages, then carries out the same ste

ps of (1), (2), (3), (4) as shown in the above o

utgoing call flow till the mobile station rings.

(11) The mobile subscriber offhooks to answe

r, thus the response (connection) message is

sent back to the fixed network

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.