Presentation on:

GSM BASICS

Presented by:Sandip ThakkarSaurabh Gandhi

Fixed line telephones

What are the drawbacks ?

• No mobility

• Delay in new connections

• Security Hazards

• Prone to failures (line disconnection, etc)

• Very less value added services

What is GSM?

Global system for Mobile communication

Standard defined by ETSI (European Telecommunications Standards Institute)

Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation

GSM: History

1982 CEPT initiated a new cellular system (GSM) in the 900 Mhz band.

1986 CEPT tested 8 experimental systems in Paris.

1987 MoU of allocations of frequencies.(uplink and downlink)

1991 First official call in the world with GSM on 1st July.

1992 New freq. allocation for GSM 1800.

1995 There were 117 GSM networks operating around the world.

2006 >1300 miilion subscribers in the world & >45 millions subscribers in india.

Aim : to replace the incompatible analog system

Evolution

1G 3G2G+

2G

GSM in world Arab world

Asia pacific

Africa

East central asia

Europe

Russia

India

North amer-ica

South amer-ica

43%

37%

4%

3%

3%

3%4%

3%3%

1%

INDIA

GSM in INDIA

Bharti

BSNL

Reliance infocom

Hutch

Idea

Reliance GSM

Tata indicom

Others

21.91%BHARTI

19.2%BSNL

17.24%Relianceinfocom

18.04%Others

5.43%Tata

10.11%HUTCH

Reliance GSM

5.973%Idea

2.075%

GSM Specifications-1

RF Spectrum

GSM 900 Mobile to BTS (uplink): 890-915 Mhz BTS to Mobile(downlink):935-960 Mhz Bandwidth : 2* 25 Mhz

GSM 1800 Mobile to BTS (uplink): 1710-1785 Mhz BTS to Mobile(downlink): 1805-1880 Mhz Bandwidth : 2* 75 Mhz

GSM-900 System Specifications

Frequency Range : 890 MHz to 915 MHz for Uplink

935 MHz to 960 MHz for Downlink.

Uses TDMA technology for Downlink / Uplink.

124 Reusable Spot frequencies of 200 kHz bandwidth each.

Each Spot Frequency carries 8 Time slots for Traffic/Signalling.

Compatible to ISDN & PSPDN.

Modulation Method : GMSK

Modulation data rate : 270.833 Kbps

Performance characteristics of GSM

Communication

Total mobility

Worldwide connectivity

High capacity

High transmission quality

Security functions

Greater QOS

CONSIDERATIONS

FREQUENCY

CAPACITY

COVERAGE

The Cell

Cellular Radio involves dividing a large service area

into regions called “cells.”

BTS

BTS

BTS

BTS

BTS

BTS

BTS

Cell Size:

LARGE CELL(35 Km)

SMALL CELL(1 Km)

Frequency & ARFCNu

l= 8

90 t

o 9

15 M

Hz

dl=

935

to

960

MH

z

Ful(n) = 890.0 + (0.2) *n MHz

Fdl(n) = Ful + 45 MHz

where n =ARFCN ; 1 n 124

GSM Services

Tele-services Bearer or Data Services Supplementary services

Tele Services

Telecommunication services that enable voice communication via mobile phones

Offered services

- Mobile telephony

- Emergency calling

Bearer Services

Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 to 9600 bps

Short Message Service (SMS) up to 160 character alphanumeric data transmission to/from the mobile terminal

Unified Messaging Services(UMS)

Voice mailbox

Electronic mail

Supplementary Services

Call related services :

o Call Waiting- Notification of an incoming call while on the handset

oCall Hold- Put a caller on hold to take another call

oCall Barring- All calls, outgoing calls, or incoming calls

oCall Forwarding- Calls can be sent to various numbers defined by the user

oMulti Party Call Conferencing - Link multiple calls together

oCLIP – Caller line identification presentation

oCLIR – Caller line identification restriction

oCUG – Closed user group

GSM System Architecture

BSC

BSC

MSC

MS

MS

MS BTS

BTS

BTS

GMSC

PSTNISDNPDN

EIRAUC

HLR

VLR

OMC

SMSC

VMSC

GSM System Architecture-I

Mobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)

Base Station Subsystem (BSS)Base Transceiver Station (BTS)Base Station Controller (BSC)

Network Switching Subsystem(NSS)Mobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR)

Mobile Station

Mobile Station consist of two units

1)Mobile handset

2) SIM(Subscriber Identity Module)

Mobile Station (MS)

A Typical Handset Consists of the following parts:

• A microscopic microphone, A speaker, An LCD or plasma display, A mini keyboard, An Antenna, A battery, A Circuit board, SIM

MS is the radio mobile terminal carried by the subscriber

MS consists of User independent HW and SWSIM (Subscriber Identity Module)

MS can be identified by IMEI (Intl Mobile Equipment Identity)

MSs have transmit power of 2W and 1W

IMEI

The Mobile Equipment is identified inside any GSM network by the International Mobile Equipment Identity (IMEI)

The IMEI is a 15-digit number

IMEI = TAC/ FAC/ SNR/ SP

TAC = Type Approval Code, determined by the main body of the GSM (6 digits)

FAC = Final Assembly Code, identifies the maker (2 digits)

SNR = Serial Number (6 digits)

SP = A spare supplementary number (1digit)

SIM stands for "Subscriber Identification Module"

SIM cards are small ‘smart’ cards that fit inside phones based on GSM technology.

SIM

SIM Uniquely associated to a user

Not to an equipment, as in first generation cellular networks

Stores user addresses IMSI MSISDN Temporary addresses for location, roaming, etc

Authentication and encryption featuresAll security features of GSM are stored in the SIM for max. protection

subscriber’s secret authentication key (Ki) Authentication algorithm (“secret” algorithm - A3 – not unique) Cipher key generation algorithm (A8)

Personalization SIM stores user profile (subscribed services) RAM available for SMS, short numbers, user’s directory, etc

Protection codes PIN (Personal Identification Number, 4-8 digits) PUK (PIN Unblocking Key, 8 digits)

MSISDN (Mobile Subscriber ISDN Number)

MSISDN: the “usual” telephone numberStructure:

CC/NDC/SN

CC : Country Code(up to 3 digits)NDC : National Destination Code (3 digits ,for PLMN)SN : Subscriber Number (max 10 digits)

IMSI

The IMSI has the following:

MCC / MNC / MSIN where

MCC: Mobile Country Code (2 or 3 digits, 404 for INDIA)

MNC: Mobile Network Code (2 digits)

MSIN: Mobile Station Identification Number (max 13 digits)

Temporary addresses

TMSI – Temporary Mobile Subscriber

Identity

32 bits assigned by VLR within an administrative area

has significance only in this area

transmitted on the radio interface instead of IMSI

reduces problem of“eavesdropping”

MSRN –Mobile Station Roaming

Number

An MSISDN number• CC, NDC of the visited

network• SN assigned by VLR

Used to route calls to a roaming MSSubscriber Number (SN)assigned to provide routinginformation towards actuallyresponsible

Base Station Subsystem (BSS)

Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers

1. Base Transceiver Station (BTS)

2. Base Station Controller (BSC)

BTS

TCBSC

BSC

TCBTS

BTS

Base Transceiver Station (BTS):

SHELTER +Transmission Medium +TOWER

BTS has a set of Transceivers to talk to MS.

One BTS covers one or more than one cell.

Capacity of BTS depends on no of Transceivers.

BTS is connected to BSC via A’bis interface.

Transmission rate on A’bis is 2 Mbps (G.703).

Interface between MS & BTS is called Air I/f.

Transmission rate on Air interface is 13 Kbps.

BTS controls RF parameters of MS.

Each TRx has 8 TDMA channels to carry Voice & signalling

BTS

A BTS in general has the following units:

Transceiver (TRX)

Power unit

Combiner

Duplexer

Antenna

Alarm extension system

Transmission unit

Baseband receiver unit (BBxx)

Nokia BTS’s

Nokia ultrasite

Nokia metrosite

Nokia flexisite

1-12 1-4 1-24 TRx capacity

Max Tx power(dBm

)

43

30

49.5

Base Station Controller (BSC)

• BSC controls several BTSs.

• BSC manages channel allocation, & Handover of calls from one BTS to another BTS.

• BSC is connected to MSC via A interface.

• Transmission rate on A I/f is 2 Mbps (G.703).

• Interface between BSC & BTS is called A’bis I/f.

• BSC has database for all of its BTS’s parameters.

• BSC provides path from MS to MSC.

1 BSC may control up to 40 BTS

BSC

BTS & BSC

Tasks of a BSS are distributed over BSC and BTS

Functions BTS BSCManagement of radio channels XFrequency hopping (FH) X XManagement of terrestrial channels XMapping of terrestrial onto radio channels XChannel coding and decoding XRate adaptation XEncryption and decryption X XPaging X XUplink signal measurements XTraffic measurement XAuthentication XLocation registry, location update XHandover management X

Transcoder and Sub multiplexer

TC

64 kbps

16 (13+3) kbps

13 kbps16 kbps (90 Channels)

16 kbps

TCSM

MSC

BTS

BSC

SMUX

TC

TC

Taking care of speech transcoding,

For transmission over the air interface, the speech signal is compressed by the mobile station to

13Kbits/s (Full Rate) or 5.6Kbits/s (Half Rate).

TCSM incorporates the transcoder and the sub-multiplexer into one piece of hardware.

Minimum possible PCM line: 4 Maximum (half rate channel): 7

TC enable also (DTx=discontinous transmssion)

In NOKIA =TCSM2E(European version) or TCSM2A(American version)

Network Switching Sub-System (NSS)

Elements:Mobile Switching Center (MSC) / Gateway MSC (GMSC)Home Location Register (HLR ) / Authentication Center (AuC)Visitor Location Register (VLR)Equipment Identity Register (EIR)

Functions:Call controlUser management

Inter-component communication:Via SS7 signalling networkWith suitable extensions (e.g. MAP – Mobile Application

Part)

Mobile Switching Center (MSC)

Heart of the network

Manages communication between GSM and other networks

Call setup function and basic switching

Call routing

Billing information and collection

Mobility management- Registration- Location Updating- Inter BSS and inter MSC call handoff

MSC does gateway function while its customer roams to other network by using HLR/VLR.

database per operator (PLMN)

HLR entries: Every user / MSISDN that has subscribed to the operator

Stores: Permanent information

associated to the user

• IMSI, MSISDN• Services subscribed• Service restrictions (e.g. roaming

restrictions)• Parameters for additional services• info about user equipment (IMEI)• Authentication data

Temporary information associated to the user

• Link to current location of the user:

• Current VLR address (if avail)• Current MSC address (if avail)• MSRN (if user outside PLMN)

Home location register (HLR)

Subscriber and subscription data

IMSI, MSISDN Parameters for additional

services info about user equipment

(IMEI) Authentication data

Tracking & routing information

Mobile Station Roaming No(MSRN) Temporary Mobile Station Identity Location Area Identity (LAI) where

MS has registered Used for paging and call setup

Visitor Location Register (VLR)

At most 1 database per MSC

VLR entries:Every user / MSISDN actually staying in the administrative area of

the associated MSC

Entry created when an MS enters the MSC area (registration)

NOTE: may store data for roaming users (subscribed to different operators)

Stores:

Authentication Centre (AUC)

HLR

MSC

Authentication is a process to verify the subscriber SIM.

Secret data & verification algorithm are stored in to the

AUC.

AUC & HLR combined to authenticate the subscribers.

Subscriber authentication can be done on every call, if required.

AUC

Equipment Identity Register (EIR)

EIR

MSC

All subscriber's mobile handset data is stored in EIR.

MSC asks mobile to send it IMEI & then checks it with data available in EIR.

EIR has different classification for mobile handset like, White list, Grey list & Black list.

According to category the MS can make calls or can be stopped from making calls.

VMSC & SMSC

MSC

SMSC VMSC

Voice Mail Service Centre : To provide Voice Mail service.

It has database for all the VMS subscribers & also stores voice messages for them.

Short Message Service Centre : To provide text message service.

To send short messages from mobile to another mobile subscriber.

Messages can also be sent by Manual Terminal connected to SMSC.0

OMC All the network elements are connected to OMC.

OMC monitors health of all network elements & carry out maintenance operation, if required.

OMC link to BTSs are via parent BSC.

OMC keeps records of all the faults occurred.

OMC can also do Traffic analysis.

OMC may prepares MIS Report for the network.

OMC

GSM Terrestrial Interfaces

Broadly classified into two types of interfaces -

Standard Interfaces

2 Mbps Trunks (E1)

Signalling System No.

7 SS7 ( CCS7)

X.25 (Packet Switched

Mode)

GSM Interfaces

Air interface: MS-BTS Abis interface: BTS-

BSC Ater interface: BSC-

TCSM A interface: TCSM-MSC Gb interface: MSC-

SGSN X.25(protocol): MSC-

DCN

GSM Operation

Speech decoding

Channel decoding

De-interleaving

Burst Formatting

De-ciphering

DemodulationModulation

Ciphering

Burst Formatting

Interleaving

Channel Coding

Speech coding

Radio Interface

Speech Speech

13 Kbps

22.8 Kbps

22.8 Kbps

33.6 Kbps

33.6 Kbps

270.83 Kbps

GSM Framing

0 1 2 3 4 5 6 7

3

Tail

bit

s

57

Coded

data

1

Steal

ing

bit

26

midambl

e

1

Steal

ing

bit

57

Code

d

data

3

Tail

bits

8.25

Guar

d

perio

d

120 ms

4.615 ms

6.12 ms

576.92 micro sec

51 Multiframes

26 frames

8 time slots

Superframe

Multiframe

Frame

Multiple access TechniquesIn

GSM

FDD / TDMA

In GSM FDD/TDMA is used.

f

c

t

FDD is used to separate downlink and uplink.

GSM TDMA System:

In TDMA one radio freq. channel is devides into consecutive periods of time.

124 traffic channels * 8 slots/Ch = 992 simultaneous conversations

13 kbps coding data rate

Each TDMA frame contain 8 shorter periods of time

known as Time slots.

TDMA time slots are called physical channel

GSM Channels

GSM Channel

Physical Logical

Common Dedicated

SCHFCCH BCCH SDCCH

BroadcastCommon control

Dedicated control

Traffic

SACCH FACCH

RACHPCH AGCH TCH/HTCH/FTCH/EFR

Incoming Call &

Outgoing Call

PSTNcallingstation

GMSC

HLR VLR

BSSBSSBSS

MSC

MS

1 2

3

4

5

6

7

8 9

10

11 12

1316

10 10

11 11

11

14 15

17

1: Calling a GSM subscriber2: Forwarding call to GMSC3: Signal call setup to HLR4, 5: Request MSRN from VLR6: Forward responsible MSC to GMSC7: Forward call to current MSC8, 9: Get current status of MS10, 11: Paging of MS12, 13: MS answers14, 15: Security checks16, 17: Set up connection

Incoming Call

PSTN GMSC

VLR

BSS

MSC

MS1

2

6 5

3 4

9

10

7 8

1. MS sends dialled number to BSS 2. BSS sends dialled number to MSC3,4 MSC checks VLR if MS is

allowed the requested service.If so,MSC asks BSS to allocate resources for call.

5 MSC routes the call to GMSC6 GMSC routes the call to local

exchange of called user7, 8,9,10 Answer back(ring back) tone is

routed from called user to MS via GMSC,MSC,BSS

Outgoing C all

Handover

What is the purpose of HO?

What is the purpose of HO?

Call continuityCall quality

Others...

Call continuityCall quality

Others...

Reasons:

Handover due to traffic reasons

Handover due to Signal quality and strength

Four Possible Handover Scenarios:

Intra-cell handover

Inter-cell, intra-BSC handover

Inter-BSC, intra-MSC handover

Inter MSC handover

Handovers

Hard HandoffAnalog, TDMA and

GSM

Soft HandoffCDMA

Break before Make Make before Break

GSMData

HSCSD

GPRS

EDGEEGPRS

WCDMA

1998 1999 2003

WCDMAPhase I

Time

Evolution

14.4 kbps

14.4 – 57.6 kbps

64 ~ 170 kbps

384 kbps

144 - 384 kbps

384 - 2048 kbps

2002 2004 2005

Technology UpgradationThe Evolutionary Path

Thanking You……