Fresh Field Mtc 001 Section 2

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GSM SystemOverviewSection Two

GSM Architecture



¥ 2001 Freshfield Communications Limited.Company Confidential Slide 2

GSM ArchitectureGSM Architecture Network ComponentsNetwork Components

± Mobile Station

± SIM

± Base Station Sub-system

± Network Switching Sub-system

± Inter-working Functions

± Network Management Centre

± Operations and Maintenance Centre

± Interfaces Used in GSM

Summary Summary

Presentation OutlinePresentation Outline



¥

2001 Freshfield Communications Limited.Company Confidential Slide 3

At the end of this course, attendees will: At the end of this course, attendees will: ± Have an appreciation of GSM network architecture

± Have an appreciation of protocol interfaces used in GSM

ObjectivesObjectives



¥


Network Switching System

Um

Abis

A

BTS

BTS

G-MSC

BTS

BSC

PSTN

EIR

NMC

OMC

Operations and Maintenance

System

Base Station Subsystem

HLR

MSCVLR

AuC

Mobile

Equipment

GSM ArchitectureGSM Architecture



¥


PSTN

Network ComponentsNetwork Components

IWF EC

Data Network

s

MSC

VLR HLR EIR

AUC

NMC

OMC

XCDR BSC

BTS

BTS

BTS

ME

BSS

SIM



¥


SIM SIM -- Subscriber Identity ModuleSubscriber Identity Module ME ME -- Mobile Equipment Mobile Equipment

BTS BTS -- Base Transceiver StationBase Transceiver Station

BSC BSC -- Base Station Controller Base Station Controller HLRHLR -- Home Location Register Home Location Register

VLRVLR -- Visitor Location Register Visitor Location Register

MSC MSC -- Mobile Switching CentreMobile Switching Centre

EIREIR -- Equipment Identity Register Equipment Identity Register

AuC AuC -- Authentication Centre Authentication Centre

Architecture Components Architecture Components



¥ 2001 Freshfield Communications Limited.

Company Confidential Slide 7

Mobile Equipment ME

Ciphering

Algorithm

(e.g. level 2)

International Mobile

Equipment Identity

IMEI

RF Capability

(e.g. output power)

Frequency

Capability

(e.g. dual-band)

CODEC

(e.g. FR, HR, EFR)

Mobile StationMobile Station




Company Confidential

Slide 8

International Mobile

Subscriber Identity

IMSI

Personal Identification

Number (PIN)

Location Area

Identification

MSISDN

Authentication key Ki

Temporary Mobile

Subscriber Identity

TMSI

Subscriber Identity Module (SIM)Subscriber Identity Module (SIM)





Slide 9

IMEI

LAI

MSRN

MS-ISDN

IMSI

TMSI

GSM

Numbering

SIM GSM NumberingSIM GSM Numbering





Slide 10

CC NDC SN

1-3 digits Variable Variable

N(S)N

MSISDN-NOT MORE THAN 15 DIGITS

MS ISDN NumberingMS ISDN Numbering





Slide 11

MCC MNC MSIN

3 digits 3 digits Not more than 9 digits

NMSI

IMSI-NOT MORE THAN 15 DIGITS

International Mobile Subscriber Identity International Mobile Subscriber Identity





Slide 12

MSC-VLR Specific

Stored in VLR & SIM Cards

Assigned after authentication

Often changed after an operator defined time period

Size ± 4 X Octets

Temporary Mobile Subscriber Identifier Temporary Mobile Subscriber Identifier





Slide 13

CC NDC SN

1-3 digits Variable Variable

N(S)N

MSRN-NOT MORE THAN 15 DIGITS

Mobile Station Roaming Number Mobile Station Roaming Number





Slide 14

MCC MNC LAC

3 digits 3 digits 3 digits

LAI

Location Area Identifier Location Area Identifier





Slide 15

International MS Equipment Identity (IMEI)

White List Grey List Black List

International Mobile Equipment Identifier International Mobile Equipment Identifier





Slide 16

MS communicates with BTS via U MS communicates with BTS via U mm interfaceinterface MS and BTS handle cell selection and reMS and BTS handle cell selection and re--selectionselection

MS and BTS handle cell handover MS and BTS handle cell handover

MS MS--BTS CommunicationBTS Communication

U m

U m

U m





Slide 17

Modulation

CipheringBurstFormatting

BitInterleaving

ChannelCoding

Digitising &

Source

Encoding

13kbps

22.8kbps

33.8kbps

8 Timeslots

270.8kbps

Tx &Antenna

Air Air--Interface CommunicationInterface Communication





Slide 18

MSC BSS with XCDR XCDR

BSC

BTS

BTS

BTS

BTS

BTS

Base Station SubBase Station Sub--systemsystem





Slide 19

Contains RF

Hardware

Limited Control Functionality

Channel coding/decoding

Timing advance

Idle channel observation

Measurement reporting

Frequency hopping*

Traffic channel management*

Control channel management*

Encryption*

Paging*

Power control*

* Can be controlled by the BSC.

Manufacturer and service

Provider will configure as required

Supports One

Or More Cells

Antenna

System

Base Transceiver StationBase Transceiver Station





Slide 20

Controls One

or More BTSs

Control Functionality

Terrestrial Channel Management

Channel allocations

Radio Channel Management

Channel Configuration

Management

Frequency hopping*

Traffic channel management*

Control channel management*

Encryption*

Paging*

Power control*

* Can be controlled by the BSC.

Manufacturer and service

Provider will configure as required

Controls

Local

Handovers

ConveysInformation to

And From The BTSs

to MSCs

Base Station Controller Base Station Controller





Slide 21

Coder

Waveform Coding

0011101010111101100

Coder

Source Coding

111101100

Coder

Coder

GSM

64kbps --- 13kbps

Speech CodingSpeech Coding





Slide 22

Transcoder Transcoder

Can be located at BSS or MSC Can be located at BSS or MSC Essential since BSC can only accept traffic via XCDREssential since BSC can only accept traffic via XCDR

64kb/s PCM traffic channel arriving from MSC is64kb/s PCM traffic channel arriving from MSC is

compressed to 13kb/scompressed to 13kb/s

TRAU converts 13kb/s into 16kb/s for BTS transmissionTRAU converts 13kb/s into 16kb/s for BTS transmission

Gross rate of 22.6 kb/s transmission over air Gross rate of 22.6 kb/s transmission over air--interfaceinterface

Each timeslot between XCDR and BSC can support up toEach timeslot between XCDR and BSC can support up to

4 traffic channels4 traffic channels





Slide 23

MSC

BSC

BTS

BTS

BTS

BTS

BTS

BTS

1 TCH = 64 kbps

XCDR

4xE1

Links

30 TCH 30 TCH 30 TCH 30 TCH

1 TCH = 64 kbps

120 GSM Traffic Channels

1xE1 Link

4:1 Compression Ratio

64 13+3=16kb/s

Transcoder XCDRTranscoder XCDR





Slide 24

BTS BSC XCDR MSC

BTS XCDR MSCBSC

13 kb/s encoded voice / 9.6 kb/s data

16 kb/s transmission

64 kb/s transmission

Transcoder XCDR ConfigurationTranscoder XCDR Configuration





Slide 25

VLR HLR

AUC

MSC

IWF

EIR

EC

Data

Networ

ks

PSTN

Network Switching SubNetwork Switching Sub--systemsystem





Slide 26

Operations &Maintenance

Call Billing

Data

Call

Processing

Gateway to

Other Networks

Mobile Switching Centre (MSC)Mobile Switching Centre (MSC)





Slide 27

Authentication

Key and AUC

Functionality

Supplementary

Services info

Subscriber

Status

IMSI and

MSISDN

Updated by

System

MSRN

SupplementaryServices

Updated byservice provider/user

Current

Subscriber VLR

Home Location Register Home Location Register





Slide 28

Temporary Mobile

Subscriber Identity

(TMSI)

Copy of the Subscriber

Profile Field by HLR

Mobile Station

Roaming Number (MSRN)

Mobile StatusLocation Area Identity

(LAI)

Visitor Location Register Visitor Location Register





Slide 29

MS

KiRAND

A3

SRES

Network

Ki RAND

A3

SRES

Equal ?

RAND

Authentication Process Authentication Process





Slide 30






Slide 31


± Triples generated by AuC and stored in HLR ± Triples (Ki, SRES and RANDS) requested by VLR and allocated

a Cipher Key Sequence Number (CKSN)

± VLR sends RAND and CKSN of triple via MSC and BSS to the

MS (unencrypted) ± MS, using A3 and A8 algorithms and Ki on MS SIM card,

calculates SRES and CKSN unencrypted to VLR

± Within VLR, value of SRES is compared with SRES of triple for

specified CKSN

± If both match, then authentication is successful





Slide 32

MS

KiRAND

A8

Network

Ki RAND

A8

Kc

RAND

Kc

Encryption ProcessEncryption Process





Slide 33

Encryption ProcessEncryption Process

± After authentication, Kc from the assigned triple is now passed to the BSS

± MS calculates Kc from the RAND and A8 Ki on the SIM

± Using Kc, A5 and the GSM hyperframe number, encryption can

now occur over the air-interface





Slide 34

HLR

AUC

VLR

MSC

HLR

AUC

VLR

MSC

EIR

White List Grey List Black List

Equipment Identity Register Equipment Identity Register





Slide 35

MSC

2-4 wireHYBRID

Echo Canceller (EC)

Data

Networks

PSTN

Echo Canceller Echo Canceller

Combats

delay of

180ms due to

voice pattern processing in

GSM





Slide 36

BSS

RoutersMSC

Modems

FAX End user¶s network

PSTN

Inter Inter--working Functionsworking Functions





Slide 37

Network Management CentreNetwork Management Centre

Highest level in hierarchical treeHighest level in hierarchical tree Overall management of network Overall management of network

Monitors OMC regionsMonitors OMC regions

± Can take control of regional areas if required

Facilitates interconnection to other networksFacilitates interconnection to other networks

Monitors network statistics for longMonitors network statistics for long--term planningterm planning





Slide 38

OMC

NMC

OMC

MSC MSC MSC

XCDR XCDR XCDR XCDR XCDR XCDR XCDR

BSC BSC BSC BSC BSC BSC BSC BSC BSC BSC

BTSBTS

BTSBTS

BTSBTS

BTSBTS

BTSBTS

Management SystemManagement System





Slide 39

Operations and Maintenance CentreOperations and Maintenance Centre

Works under the command of the NMC Works under the command of the NMC Central point for control of BSSs, MSC and databasesCentral point for control of BSSs, MSC and databases

Management of faults, alarm systems, statistics, and Management of faults, alarm systems, statistics, and

configurationconfiguration

Two systems availableTwo systems available

± OMC-R: Allocated to the command and control of all BSSs and

interconnecting links

± OMC-S: Allocated to the command and control of all network

switching sub-system and interconnecting links





Slide 40

OMC (R)

BSS

OMC (S)

Network

Switching

System

OMC

FunctionsConfiguration

Management

Fault

Management

Security

Management

Performance

Management

Event/Alarm

Management

Operations and Maintenance CentreOperations and Maintenance Centre





Slide 41

Interfaces Used in GSM Interfaces Used in GSM

2Mb/s trunks (E1)2Mb/s trunks (E1) ± Bearer of speech, data and control signalling around network

Signalling system ITU Signalling system ITU--T SS7 or C T SS7 or C--7 7

± Standard method for signalling between digital exchanges

X.25 Packet X.25 Packet--switched dataswitched data

± Used to transport subscriber queries, authentication,

equipment identity numbers, etc.

Abis using LAPD protocol Abis using LAPD protocol

± Main control protocol between BSC and BTS





Slide 42

IWF EC

MSCVLR

EIR

NMC

OMCXCDR

BSC

Data

NetworksPSTN

BTS

BSC

BTS BTS

BTS

IWFEC

MSC

VLR

HLR

XCDR

BSC

BTS

BSC

BTSBTS

BTS

AUC

Network Interconnectivity Network Interconnectivity





Slide 43

IWFEC

MSCVLR

EIR

NMC

OMCXCDR

BSC

Data

NetworksPSTN

BTS

BSC

BTS BTS

BTS

IWFEC

MSC

VLR

HLR

XCDR

BSC

BTS

BSC

BTSBTS

BTS

AUC

E1/T1 LinksE1/T1 Links





Slide 44

IWFEC

MSCVLR

EIR

NMC

OMCXCDR

BSC

Data

NetworksPSTN

BTS

BSC

BTS BTS

BTS

IWFEC

MSC

VLR

HLR

XCDR

BSC

BTS

BSC

BTSBTS

BTS

AUC

SS7 Signalling InterfacesSS7 Signalling Interfaces





Slide 45

IWF EC

MSCVLR

EIR

NMC

OMCXCDR

BSC

Data

NetworksPSTN

BTS

BSC

BTS BTS

BTS

IWFEC

MSC

VLR

HLR

XCDR

BSC

BTS

BSC

BTSBTS

BTS

AUC

Abis LAPD Interfaces Abis LAPD Interfaces





Slide 46

IWF EC

MSCVLR

EIR

NMC

OMCXCDR

BSC

Data

NetworksPSTN

BTS

BSC

BTS BTS

BTS

IWFEC

MSC

VLR

HLR

XCDR

BSC

BTS

BSC

BTSBTS

BTS

AUC

X.25 Interfaces X.25 Interfaces





Slide 47

Summary Summary

GSM architecture reveals a highly complex but GSM architecture reveals a highly complex but hierarchical system.hierarchical system.

System inter System inter--working is designed to allow for working is designed to allow for

appropriate subscriber management includingappropriate subscriber management including

authentication, encryption and location updatingauthentication, encryption and location updating Knowledge of the components of this architecture areKnowledge of the components of this architecture are

essential for a good understanding of call sequences inessential for a good understanding of call sequences in

GSM GSM

Documents

Fresh Field Mtc 001 Section 2