Gsm basics

ObjectivesObjectives Understand Concept of Cellular Understand the functional blocks in a GSM Network Understand the Air Interface with Channels Understand Mobile Call Setup Operations

Basics

Agenda Need for Cellular Introduction to Cellular Channelization Concept GSM Evolution and Markets GSM Network Arhcitecure GSM Air Interface Parameters GSM Speech Coding Physical and Logical Channels Frames and MultiFrames GSM Basic Operations

Telephony Communication is today's basic need Telephone has become part of life

Fixed Line Telephones

What are the drawbacks ?

Fixed Line Telephones No Mobility

Delay in New Connections

Security Hazards

Prone to Failures ( Line Disconnection, etc )

Very less value added services

Mobile Communications Drawbacks of Fixed Phones have

triggered wireless communications

"Call People , Not Places ""Call People , Not Places "

MCG Spokane Division RTEd Sem, 1000-1268 9/93Company ConfidentialH

First Wireless Signal

3Postcard: Chicago Daily News

Wireless Access Methods

Authoring Division Name File NameSecurity Notice (if required)

H

Wireless Communication Model

Source

DisplayTransmitter

Receiver

Media of transmission is Radio Frequency


H

Types of Wireless Communications

Simplex

The direction of transmission is in one direction only

BEEP

Ex : Broadcast Services ( AM/FM Radios, Television ) Paging Services


H

Types of Wireless CommunicationsHalf -

DuplexThe direction of transmission is alternate in both directions

Tx

Rx

Tx

Rx

"A"

"B"

A transmits -- B receives, thenB transmits -- A receives

Ex : PTT Handsets, Trunked Radios


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Types of Wireless CommunicationDuple

xThe direction of transmission is simultaneous in both directions

Ex : Cordless Telephones, Mobile Phones, Microwave Radios

Is there separate frequency of transmission at both ends ?


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The Electromagnetic Spectrum

MICROWAVES

AM

BR

OA

DC

AS

T R

AD

IO

SH

OR

T-W

AV

E

RA

DIO

MO

BIL

E R

AD

IO

VH

F T

V

FM

BR

OA

DC

AS

T

RA

DIO

MO

BIL

E R

AD

IOV

HF T

V

FIB

ER

OP

TIC

S

CO

MM

UN

ICA

TIO

N

VIS

IBLE L

IGH

T

1MHz

10MHz

100MHz

1GHz

10GHz

100 GHz

10

1210

14 1

0

15

MF HF VHF

UHF SHF EHF

1µm

1000m

100m

10m

1m

10cm

1cm

1mm

Wireless Communication !!! At what frequency ?


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Selection of Band for Wireless Communication

MF : 300 KHz - 3 MHz ( Domestic Radios )HF : 3 MHz - 30 MHz VHF : 30 MHz - 300 MHz ( FM, Paging, PTT )UHF : 300 MHz - 3 GHz ( Mobile Radios, Cordless Phones )SHF : 3 GHz - 30 GHz ( Microwave Band )

Properties of Radio FrequenciesLow Frequency - Less Loss ,,, High Frequency - More Loss

To overcome loss , more power required, More Power - Health hazardsLow Frequency - High Beamwidth - Wider and Deeper Coverage

Selection of Band will depend on ApplicationFrequency Band is subdivided into Application BandApplication Band is further divided into Technology Channels


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Channelization

Frequency Band has several application segments Certain blocks of the Band are reserved for certain applications by

regulating authorities and as well by standard Technologies Technologies have decided on fixed bandwidth Channels within these bands

Example : Mobile CommunicationsAMPS / DAMPS : 824 MHz -- 894 MHz ( 50 MHz + 20 MHz

separation)GSM : 890 MHz -- 960 MHz -- ( 50 MHz + 20 MHz separation)

These 50 Mhz are bands are further divided into Channels

Channelization can be done by three methods

--- FDMA --- TDMA --- CDMA


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Channelization Methods

FDMAPower

Frequency

Time

FDMA

Ex: AMPS / DAMPS band is divided into 30 Khz Channels ( 1666 Freq Chs) GSM band is divided into 200 Khz Channels ( 250 Freq Chs ).

Television Channels ( Star, Zee, Sony, MTV, BBC, CNN etc. )


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Frequency

Power Time

FDMA/TDMA

TDMA

Each FDMA Channel is divided into Timeslots Each Timeslot is of fixed period This method increases the number of Channels in a

systemEx: DAMPS has 3 timeslots on each 30 Khz Channel ( 4998 Channels) GSM has 8 timeslots on each 200 Khz Channel ( 2000 Channels )


H


CDMA

FrequencyCDMA

Power

Time

Frequency Channel is divided into Code Channels 1.25 MHz of FDMA Channel is divided into 64 Code

Channels


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Mobile Telephony -- Channelization

Mobile Telephony needs Duplex Communication

How many Channels will be required for one call ?

What type of Channels ? -- FDMA, TDMA, FDMA/TDMA , FDMA/CDMA or something else


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Duplex Access Methods

Frequency Division Duplex(FDD)

Frequency

Amplitude

Time

F1 F2

Tx RxTime Division Duplex

(TDD)

Frequency

Amplitude

Time

F1

TxTx

Rx

Rx

Introduction to Cellular Communications

Need for Cellular

Cellular network has cells of different sizes. Bigger cells are used where

subcriber density is low. Smaller cells are used where subscriber density is high.

Cellular structure

High

way

Cell Configuration

Omnidirectional Cell

BTS

Sectorial Cell

BTS

Frequency Reuse

GSM uses concept of cells One cell covers small part of network Network has many cells Frequency used in one cell can be used

in another cells This is known as Frequency Re-use

F=1

F=2F=3

F=4,8

F=5,9

F=6,10

F=7

F=1

F=2F=3

F=4,8

F=5,9

F=6,10

F=7

F=1

F=2F=3

F=4,8

F=5,9

F=6,10

F=7

F= 1,2,3,4,5,6,7,8,9,10

Clusters

Co-Channel ( Re-use ) Cells

Distance between two cellsusing same frequencies

1,13,29D

D=R x SQRT( 3 x N )

N= Cluster size ( 7 in this case ) R=Radius of one cell D=Dist between two cells using same channels

1,13,29

1,13,29

1,13,29D R

Cell Splitting

Macro Cell

Macro Cell

Micro Cells

Micro Cells

Pico Cell

Macro Cell

Authoring Division Name File NameSecurity Notice (if required) H

GSM TECHNOLOGY - Standards & Implementation.

GSM900DCS1800


GLOBAL System for Mobiles

GSM900

239 licenses in 109 countries now

44 million subscribers now

One New subscriber Every Second !

> 200 million subscribers by Year 2000


Personal Communications Networks

USA: PCS1900for new PCS

UK: DCS1800Mercury One-2-OneMicrotel-Orange

Germany: DCS1800E Net

France: DCS1800For new PCN

Australia: DCS1800for new PCN

Thailand: DCS1800AIS

DCS1800PCS1900

Hong Kong: DCS1800for 6 New PCNs


Evolution of GSM GSM Requirements

Good subjective speech quality Encryption of user information Must operate in the entire 890 - 960 Mhz frequency band Spectral efficiency Support for international roaming Minimize modifications to the existing fixed public networks Low handsets and service cost ISDN compatibility Support for range of new services and facilities


The Global Standard


Other GSM standards

GSM 900 and DCS 1800 use the same standards DCS 1800 specs are defined as a delta standard to GSM specs Same GSM switches can be used for DCS 1800 Some software upgrading may be required ( if RR are manged by switch ) Dual Mode handsets will be required to support both

PCS 1900

DCS 1800

ETSI has assisted ANSI T1 and TIA TR-46 committees to formulatespecs for PCS 1900.


Evolution of GSM

1982 : Group Special Mobile formed within CEPT 1986 : A permenent Nucleus formed 1987 : Radio transmission Techniques are chosen.Field

trials completed 1987 : GSM becomes ETSI technical committee 1987 : 13 Operators sign a memorandum of uderstanding 1989 : Prototype ( validation ) systems are on the air 1990 : GSM Phase I specifications are finalised 1991 : UK,France,Germany andItaly introduce GSM services 1992 : Motorola cuts over the first commercial system built

for COMVIQ on Sept 1 1994 : GSM Phase 2 specifications released 1996 : GSM Phase 2+ specs are now defined GSM Phase I specification document has 5230 pages !!!

The History


Growth


Technology Evolution


GSM 2G+


IMT-2000 / 3G+(International Mobile Telecommunications -2000)


GSM Standards structure

01 Series : General02 Series : Service aspects03 Series : Network aspects04 Series : MS-BS interface and protocols ( air interface layer 2 & 3)

05 Series : Physical layer on the Radio path ( air interface layer 1)

06 Series : Speech coding specs.


GSM STANDARDS - Continued

07 Series : Terminal adaptation for mobile stations 08 Series : BSS - MSC interfaces ( A & Abis) 09 Series : Network interworking10 Series : Empty - For future use11 Series : Equipment and Type approval specifications12 Series : Operation & Maintenance

MS

BTS

BTS

BTS

BTS BTS

BTS

BTS

BTS

BSC

BSC

PSTN

VLR

TRAU HLREIR

OMC

SMSC

BC

AUC

VMSC

MSC

Abis

A

OML

GSM Network Architecture

BTS

BTS

BTSMS

MS

EIR

AUC

HLR

VLR

MS - Mobile Station Mobile station provides user access to GSM network for Voice & Data. All GSM mobiles comply to the GSM standards. Subscriber data is read from a SIM card that plugs into MS. Each MS has a unique number called as IMEI number, which is stored in EIR for authentication

purposes. Mobile camps on to the GSM network through a BTS serving the cell. Mobile also scans neighbouring cells and reports signal strength. Network knows whereabouts of mobiles from HLR & VLR databases. Mobile Transmit and Receive voice at 13 KB/s over air interface.

SIM

H GSM Course

Mobile Station Output Power

CLASS 1 20 watts Vehicle and Portable

CLASS 2 8 watts Portable and Vehicle

CLASS 3 5 watts Hand-held

CLASS 4 2 watts Hand-held

CLASS 5 0.8 watts Hand-held

Output Power determines: ---- Accessibility in areas of

coverage ---- Talk time and Standby Time Output Power on call is varied as commanded by

BTS

MS - Mobile Station

H GSM Course

Mobile Station Identities

MSISDN : Human Identity used to call a Mobile Station

CC NDC SN

98 XXX 12345

IMEI: Serial number unique to every Mobile Station TAC FAC SNR SP

6 digits 2 digits 6 digits 1digit

H GSM Course

SIM - Subscriber Identity Module

GSM

Removable Module inserted when the subscriber wants to use the MS

IMSI : Network Identity unique to a SIM

MCC MNC MSIN404 XX 12345

3 digits

2 digits

10 digits

Two Sizes

Credit Card Stamp Size

4-8 digits PIN code 3 false entries - blocks 8 digit PUK 10 false entries -

disabled

MS

ROM = 6kb to 16kbRAM = 128 byte to 256 byteEEPROM = 3 kb to 8 kb

H GSM Course

SIM - Subscriber Identity Module

Contents of SIM Serial Number IMSI, Subscriber Key ( Ki ) Algorithms for Authentication, Ciphering Network Code PIN, PUK Charging Information Abbreviated Dialling Supplementary Features ( e.g. call barring

)

SIM features and contents are personalized by the Service Activator

MS also stores some temporary data on SIM during operation

H GSM Course

Base Station Cell Site Architecture

MainsPowerPanel

DCPowerSupplyUnit

BatteryBackup

Abis

BTSDMR

GSM Antenna System

BTS Cabin/Shelter/Room

AirCon

H GSM Course

BTS - Base Transceiver Station

BTS

MS

BSC MSC

CELL

BTS has a set of Transceivers to communicate with mobile's in its area One BTS covers one or more than one cell The capacity of a cell depends upon number of tranceivers in a cell. BTS is connected to the BSC through Abis Interface, which is a 2Mb/s BTS transmit and receive voice at 13 kbps over air interface to the

mobiles. BTS commands mobiles to set Tx. power, timing advance and Handovers

RF ChannelsAbis - 2 MBits/s

H GSM Course

BTS Architecture 1

BSC

TxRx A Rx B

Splitter

Processor Modules

T S B

P P

PCMInterface

AlarmInterfac

e

A1

TRX TRX1 2

B1

A2

B2

TRAU

BTS

COM

RFUBPF

Fr

Ref

H GSM Course

BTS Architecture 2

TRX Logic

TRX RF

Power Amplifier

TRX Unit

PSU & Climate Control

Antenna

ABIS over G703

Backplane

BTS Cabinet. 3 Channel. Single Sector

I Q

RF

I Q

Combiner / Distribution Unit

Rx FilterLNA

Sp

litte

r

Combiner Du

ple

xe

r

CouplerCoupler

Interface

Frequency Reference

Unit

CPUBTS

Alarms

NEMProprietary Interfac

e

H GSM Course

BSC - Base Station Controller

Several BTS's are connected to one BSC BSC manages channel allocation,handovers and release of channels at connected

BTS's BSC connects to each BTS on an Abis interface & to the MSC on A interface BSC has the entire database for all cell parameters associated with the BTS's.

MSC

Abis

A

H GSM Course

Base Station Controller

BTS

Processor Modules

P

C

M

P

C

M

P

C

M

T S B

P P

TM

G

TRAU

MSC

BSC

H GSM Course

Abis Interface

E1 / T1

Abis is a G.703 interface. It could be E1 or T1 Abis carrries Traffic information of all the mobiles in the cells controlled by

the BTS. Abis also carriers signalling information between BTS and BSC Signaling over Abis is done by LAPD protocols LAPD has several modes of implementation

--- LAPD--- LAPD Concentrated--- LAPD Multiplexed

H GSM Course

Abis Interface

LAPD ModesLAPDSignaling for each TRX is on a dedicated 64 Kbps circuitMaximum Signalling for 10 Transceivers on 1 E1 link

64 kbps 0 Sync64 kbps 1 TRX Signaling64 kbps 2 4 Traffic Channels64 kbps 3 4 Traffic Channels64 kbps 4 TRX Signaling64 kbps 5 4 Traffic Channels64 kbps 6 4 Traffic Channels64 kbps 7 TRX Signaling64 kbps 8 4 Traffic Channels64 kbps 9 4 Traffic Channels

} 1 TRX

} 1 TRX

} 1 TRX

H GSM Course

Abis Interface

LAPD ModesLAPD Concentrated mode 1Signaling for 4 TRX's is on a dedicated 64 Kbps ciruitMaximum Signalling for 13 Transceivers on 1 E1 link

64 kbps 0 Sync64 kbps 1 4 x TRX Signaling64 kbps 2 4 Traffic Channels64 kbps 3 4 Traffic Channels64 kbps 4 4 Traffic Channels64 kbps 5 4 Traffic Channels64 kbps 6 4 Traffic Channels64 kbps 7 4 Traffic Channels64 kbps 8 4 Traffic Channels64 kbps 9 4 Traffic Channels

64 kbps 10 4 x TRX Signaling

} 1 TRX

} 1 TRX

} 1 TRX

} 1 TRX

H GSM Course

LAPD ModesLAPD Concentrated mode 2Signaling for All TRX's is on a dedicated 64 Kbps ciruitMaximum Signalling for 15 Transceivers on 1 E1 link

64 kbps 0 Sync64 kbps 1 ALL TRX Signaling64 kbps 2 4 Traffic Channels64 kbps 3 4 Traffic Channels64 kbps 4 4 Traffic Channels64 kbps 5 4 Traffic Channels64 kbps 6 4 Traffic Channels64 kbps 7 4 Traffic Channels64 kbps 8 4 Traffic Channels64 kbps 9 4 Traffic Channels

64 kbps 10 4 Traffic Channels

} 1 TRX

} 1 TRX

} 1 TRX

} 1 TRX

Abis Interface

H GSM Course

Abis Interface

LAPD ModesLAPD MultiplexedSignaling for each TRX is on 16kbps subchannel.Maximum signalling for 15 TRX's on

64 kbps 0 Sync64 kbps 1 TRX Signaling/ 3 Traffic Channels64 kbps 2 4 Traffic Channels64 kbps 3 TRX Signaling/ 3 Traffic Channels64 kbps 4 4 Traffic Channels64 kbps 5 TRX Signaling/ 3 Traffic Channels64 kbps 6 4 Traffic Channels64 kbps 7 TRX Signaling/ 3 Traffic Channels64 kbps 8 4 Traffic Channels64 kbps 9 TRX Signaling/ 3 Traffic Channels

64 kbps 10 4 Traffic Channels

} 1 TRX

} 1 TRX

} 1 TRX

} 1 TRX

} 1 TRX

TRAU - Transcoder / Rate Adaptation Unit

The MSC is based on ISDN switching. The Fixed Network is also ISDN based ISDN has speech rate of 64kbps. Mobile communicates at 13 Kbps TRAU converts the data rates between 13 KB/s GSM rate to 64 Kbits /s Standard ISDN rate TRAU can be colocated with the BTS,BSC or MSC or it can be a separate unit.

MS

MS

RF Channels

BTS BSC

MSC

TRAU

Abis interface 2 MBits/s

A interface 2 MBits/s

13 KBits/sec

PSTN

16 KBits/sec 16 KBits/sec 64 KBits/secVOICE

H GSM Course

LOCATION OF TRANSCODER

Colocated with MSC,BSC,BTSSeparate Unit

16 kbps

64 kbps BSCTranscode

rMSC

H GSM Course

MSC - Mobile Switching Centre

Exchange where calls are established,maintained and released. Database for all subcribers and their associated features. Communicates with BSC's on MS side and with PSTN on fixed line

side. MSC is weighted on the number of subcribers it can support

BSC's

BTS'sHLR

VLR

MSC

H GSM Course

MSC - Mobile Switching Centre

Multiple MSC's

BSC's

BSC's

MSC

MSC

GMSC

More subscribers ? More MSC's !

H GSM Course

HLR - Home Location Register

HLR

MSC has all subscriber database stored in HLR HLR has all permanent subscriber database MSC communicates with HLR to get data for subscribers on

call

HLR will have the series of all subscriber numbers, which may not be activated or issued .

H GSM Course

VLR - Visiting Location Register

VLR

HLR

A subscribtion when activated is registered in VLR VLR has all the subscriber no's which are activated VLR also has temporary database of all activated subscribers ( on/off,

location )

MSC communicates with HLR for susbcribers coming from different MSC'sand if found valid, then registers them in its VLR

H GSM Course

AUC - Authentication Centre

HLR AUCMSCMS

Authentification is a process by which a SIM is verified Secret data and the verification process alogorithm are stored at

AUC AUC is the element which carries out the verification of SIM AUC is associated with the HLR

H GSM Course

EIR : Equipment Identity Register

EIR is the Mobile Equipment Database which has a series of IMEI's

MSC asks the Mobile to send its IMEI MSC then checks the validity of IMEI with the EIR All IMEI are stored in EIR with relevant classfications

EIR

MSC

Classifications of IMEI( Mobile Stations )

White List Grey List

Black List

H GSM Course

BC - Billing Centre

BC

BC Generates the Billing Statement for each Subscriber BC may be directly connected to the MSC MSC sents the billing information ( duration of call ) to BC BC then produces the billing amount based on the units set

H GSM Course

OMC - Operations & Maintenance Centre

It is central monitoring and remote maintenance centre for all network elements

OMC has links to BSC's and MSC

OMC Terminals

BTS's

BTS's

BTS's

OMC System

BSC's

MSC

asasasaaaaaaqwtttsssdfaaqwrqrncnceas



H GSM Course

OMC - Operations & Maintenance Centre

BTS's

BTS's

OMC System

BSC's

MSC



OMC - R OMC -

S

H GSM Course

OMC - RADIO

BTS BTS BTS BTS

BSC BSC

TRANSCODER

MSC

MUX / DEMUX

SERVER OMC - R

X.25 SWITCH

H GSM Course

OMC - Functions

En viron m en tal Alarm sPower , F ire, Secu rity,

Aircon s, etc.

Eq u ip m en t F ailu re Alarm sBTS, BSC site F ailu res

MSC an d p h erip h eral failu res

A larm M onitoring

Ad d n ew h ard wareMod ify con trol p aram etersoth er software ch an g es.

C onfiguration C hanges

Cell Traffic An alysisNo of calls, o/g ,i/c

PSTN, Call d rop s etc.

P erform ance A nalysis

OM C Functions

H GSM Course

Equipment Alarms

BTS , BSC , Transcoder Failures

Link Failures

Module Failures ( Transceiver,Processors)

NetworkBTS A

Transceiver 1 Fail

17:35hrs Site A Transceiver 1 Fail

H GSM Course

Cell Traffic

0

1

2

3

4

5

6

7

8

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3

cell names

TCH TRAFFIC IN ERLANGS FROM 09:00 to 21:00hrs

1

H GSM Course

SMSC - Short Message Service Centre

Message is sent to a particular mobile. Message transfer takes place through SMSC Messages are be sent through a Manual Terminal connected to

SMSC

SMSC

MSC

H GSM Course

VMSC : Voice Mail Service centre

VMSC

MSC

It has a database for all Voice Mail Subscribers It also stores all the Voice Mail - Voice

Messages

H GSM Course

GSM Signaling Interfaces

VLR

HLR/AUC

EIR

PSTN GMSC GSMSC

VLR

HLR/AUC

Abis A

B

C

F

E

G

D

SS7/R2

MSCBSC

BTS

OMLOMC

A,B,C,D,E,F,G,H,I = SS7Abis = LAPDOML = X.25

SUPP

I

H

A GSM Cell

Broadcast CHannel

Traffic CHannel

UPLINK

890-915 MHz

DOWNLINK

935-960 MHz

BTS

Abis Interface

To BSC

BCH

TCH

Separate Bands for Uplink and DownlinkDown link : 935 - 960 MHz ( E-GSM 925 - 960 MHz ) Uplink : 890 - 915 MHz ( E-GSM 880 - 915 MHz)

TDMA and FDMA Multiplex–124 Frequency Channels (ARFCN) for GSM900– 1 to 124 for current band– 975 to 1023 for E-GSM–200kHz Channels–8 Mobiles share ARFCN by TDMA

0.3 GMSK Modulation–270.833 kbits/sec. rate

Variable Tx Power and Timing

GSM Air Interface

TDMA and FDMA

1 2 3

4

5

6

7

3

4 5 67

0

1

2

Time

Frequency

Amplitude

ARFCN

Timeslot

Physical Channel is anARFCN and Timeslot

The GSM Burst

Guard

Period

Time

Frequency

Amplitude

Midamble

8.25

bits3

57 bits

126

bits1

57 bits3

Data

Tail

bits

Data

Control

bit

Tail

bit

Control

bit

Speech Coding

PSTN

Air Interface

PCM Coding - 64 KB/s

RPE-LTP Coding in GSM - 13 KB/s

RPE and LTP Coder ( Regular Pulse Excited - Long Term Prediction )

RPE-LTP is a combination of RELP and MPE-LTP codecs.

Coverts Speech to Low Data Rate

20ms Speech makes 260 Bits

Output 13 kbit/s

20 ms Blocks

Speech Coder

Bits Ordered

260 Bits

260 Bits

132 78Important Bits

Other Bits

50Very Important Bits

Speech Coder - Defined under GSM TS 6.10

Block Code

132 7850Type Ia Type Ib Type II

Re-ordering

Half rate convolutional code

CRC

50 132 783

Type Ia Type Ib Type II

378 78

Type II

25 25 78466 663

TailCRC Type Ib Type IaType Ia Type Ib Type II

262 Bits in

456 Bits Out

456

Bits from 20ms of Speech

Error Correction

Diagonal Interleaving

57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57

456 Bits from 20ms of Speech 456

Bits from 20ms of Speech

57 57 57 57 57 57 57 57 57 57 57 57 57 57

Traffic Channel (TCH) Bursts Carry Two 57 Bit Blocks (114) Each

120ms of Speech = 456x6 = 2736 bits2736 / 114 = 24 bursts i.e. 24 frames (mobile Tx once per frame)Multiframe has 26 frames in 120msThere are 2 spare frames ......One SACCH, One Idle

TCH

Convolutional Coding & Interleaving

HELLO FOLKS

HHEELLLLOO FFOOLLKKSS

ELSOLHLOFK LEOLSHOLKF

EL SOL HLOFK LEOLSHOLKF

HHEELLL -OO FFO -LLKK -S

HELLO FOLKS

Bits to be Txed:

Convolutionally Encoded:

Interleaved:

Bits Rxed:

De-Interleaved:

Viterbi Decoded:

Convolu

tion

al

Enco

de

r

Inte

rleav

er

De

-In

terle

av

er

Deco

de

rH

ello

.....

Example:

H GSM Course

Speech coding Process

20ms

Speech Coder

260 bits

50 132 781a 1b 11

Channel Coder

456 bits

13 kbps

22.8 Kbps

Tranceiver ( BTS )

22.8 Kbps456

bits

260 bits13 kbps

Transcoder Handler

260 + 60 = 320 bits

16 kbps

TRAU Frame

Abis

H GSM Course

TRAU Frame

260 bits info + 60 TRAU bits = 320 bits/ 20ms = TRAU Frame

60 bits contains Frame Information data which indicatesspeech,data,idle,O & M , full-rate/half-rate.

16 Kbps T =

T T T TSynch Sign

T0 T1 T2 T3 T30 T31Abis

60 bits = 35 synchronization + 21control + 4 timing

8 Midamble Patterns (Colour Codes) of 26 bits RACH and SCH have Longer 41 and 64 bit Midambles

Equalizer Estimates Channel Impulse Response From Midamble

Mathematically Construct Inverse Filter Uses Inverse to Decode Data Bits

Midamble or Training Bits

Timeslot

(normal burst)

Midamble

8.25bits

357 bits

126 bits

157 bits

3

GuardPeriod

Data

Tail bits Data

Controlbit

Tail bit

Controlbit

GSM TDMA Power Burst

+1.0 dB

-1.0 dB

+4 dB

-6 dB

-30 dB

-70 dB

-6 dB

-30 dB

-70 dB

147 "Useful" Bits542.8s

148 "Active" Bits, 546.42s

3 57 1 26 1 57 3

10s 8s 10s 10s 10s8s

Power

Time

0.3 GMSK Modulation

Data

Frequency

Phase

+67.708 kHz

-67.708 kHz

270.833kB/s

+90deg -90degI

Q

Uplink Lags Downlink by 3 Timeslot periods Uplink and Downlink use same Timeslot Number Uplink and Downlink use same Channel Number (ARFCN) Uplink and Downlink use different bands (45MHz apart for GSM900)

Downlink and Uplink

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1

25

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1

Downlink

Uplink45 MHz

Measurements by MS and BTS

Uplink RXLEV ( - 48 to -110 dbm )

Uplink RXQUAL ( 0 - 7 )

Downlink RXLEV ( - 48 to -110 dbm )

Donwlink RXQUAL ( 0 - 7 )

RXLEV is the received power level RXQUAL is the received quality.

It is the bit errorr measured on the M idamble

0 1 < 0.2 %2 0.2 - 0.4 %3 0.4 - 0.8 %4 0.8 - 1.6 %5 1.6 - 3.2 %6 3.2 - 6.4 %7 6.4 - 12.8 %

RXQUAL

Measuring Adjacent Cell BCH Power

UPLINK

ADJACENT CELL

BCH

DOWNLINK

RXLEV RXLEV RXLEV RXLEV RXLEV

Mobile Power Control

Mobile is commanded to change its Transmit Power Change in Power is proportionate to the Path Loss Change is Power is done in steps of 2 dbs

Tx Level567.

1415

Power dBm33 31 29 .

1513

Path LossLow RXLEV

Pwr Command

TDMA approach requires signals to arrive at BTS atthe correct time. They must not overlap.

BTS

Timing Advance

Concept of Channels in GSM

1. To pick up employees in the morning 2. To receive company guests from airport 3. To carry material to the site / stores 4. To Collect mail/courier 5. To drop the employees back home 6. To get a doctor in case of emergency 7. To carry company gusts for a dinner

If there were two vehicles, we can allocate a set of tasks to one , and rest to the other. However, since both are identicle vehicles, there is greater flexibility in usage.

Concept of Channels in GSM A company vehicle is used for several purposes in a

day..

0 1

5

6

7

4

2 3 40

1

2

3

FRAME NUMBER

TIME S

LOT

Time Sharing by Channels FCCH

SCH

BCCHBCCH

BCCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCHTCH

Concept of Frames

C T T T T T T T

C T T T T T T T

C T T T T T T T

Frame No. 1

Frame No. 2

Frame No. 3

Time slot Number.. 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

C T T T T T T T Frame No. 4

CHANNEL ALLOCATIONS IN A CELL

0

1

2

3

4

5

6

7

U1U1 U1 U1

U5 U5 U5 U5 U5 U5 U5 U5 U5

U2 U2 U2 U2 U2

U3 U3 U3 U3 U3 U3 U3

U4 U4 U4 U4 U4 U4 U4 U4

U6 U6 U6 U6 U6 U6 U6 U6

FRAME Number

U7 U7 U7 U7 U7

U8 U8 U8 U8

C CCCC C C C CC C C

Frames and Multiframes

(normal burst)

Control Channel Multiframe

Frame

Timeslot156.25 Bits

8 Timeslots

GuardPeriod

4.615ms

576.92 us

8.25bits

3

57 bits

126 bits1

57 bits

3 Data

Tail bits

Data

Controlbit

Midamble

Tail bit

Controlbit

0 12 3 4

5 6 7

0 50 0 26

Traffic Channel Multiframe

Channels in GSM Air Interface

PHYSICAL CHANNELSARFCNs - 1 to 124 ( D & U )Timeslots - 0 to 7 ( D & U )Total of 124 x 8 = 992 Channels

LOGICAL CHANNELS ARFCN - X , Timeslot - YFrame Number - N

1 2 3

45

3

4 5 60

1 2

BCH -BROADCASTCHANNELS

DCCH - DEDICATED CONTROLCHANNELS

CCCH - COMMON CONTROLCHANNELS

CONTROL CHANNELS TRAFFIC CHANNELS

PCH -PAGINGCHANNEL

FCCH - Frequency Correction Channel

SCH - Synchronisation Channel

BCCH - Broadcast Control Channel

BCH

SDCCH - Standalone Dedicated Control Channnel

SACCH - SlowAssociated Control Channnel

FACCH - FAST ASSOCIATED CONTROL CHANNEL

AGCH -ACCESSGRANTCHANNEL

RACH -RANDOMACCESSCHANNEL

TCH - F FULL RATE TRAFFIC CHANNEL

TCH - TRAFFIC CHANNEL

TCH - H HALF RATE TRAFFIC CHANNEL

TCH

One ARFCN, On all the time, in every cell Uses Timeslot 0 on a channel, in Downlink. Allows Mobiles to tune to BTS freq. - FCCH This channel carries a 142 bit zero sequence and repeats once in every 10 frames on BCH

Allows Mobile to Synchronise - SCH This channel carries the Frame number and BSIC in encrypted data format. Amidamble of 64 bits helps mobiles to synchronize. SCH also repeats once every 10 Frames.

Allows Mobiles to identify Network - BCCH Used to broadcastl Cell and Network identity. BCCH occupies 4 frames on BCH. and repeats once every Multiframe.

BCH - Broadcast CHannel

BCH

BCH Sub channels

FCCH

SCH

142 bits - all 0's3 3 8.25

StartBits

StopBits

GuardBits

33 8.2539 3964

Training Sequence

GuardBits

StopBitsStart

Bits

EncryptedData Bits

EncryptedData Bits

BCCH

3 3 8.25StartBits

StopBits

GuardBits

3 3 8.25StartBits

StopBits

GuardBits

3 3 8.25StartBits

StopBits

GuardBits

3 3 8.25StartBits

StopBits

GuardBits

BCH

57

57

57 57

57

57

57

57

26

26

26

26

CCCH shares Timeslot 0 with BCH on a Multiframe

CCCH consists of PCH , RACH & AGCH. PCH - Paging Channel is used to alert mobiles on incomming calls. PCH carries IMSI to page for Mobiles in the cell. PCH is Downlink channel.

RACH - Random Access Channel - is a short burst sent by mobile to BTS , to initiate a call request . RACH uses Timeslot 0 on reverse BCH channel on Uplink.

AGCH - Access Grant Channel - When mobile sends a RACH to BTS, BTS responds by allocating a SDCCH channel to mobile over AGCH.

CCCH - Common Control CHannel

BCH

Used by the MOBILE to get attention from BASE STATION in the Uplink.

Several mobiles might originate RACH simultaneously.

RACH uses a Slotted ALOHA access scheme. Mobile doesn't know path delay

–So RACH has to be a special SHORT BURST–Mobile sends normal burst only after getting Timing Advance on Downlink SACCH

RACH - Random Access CHannel

8 3 68.2541 36

ExtendedGuard Period

StopBits

StartBits

Synchronisation Bits

EncryptedData Bits

88 bits

BCH & CCCH - 51 Frame structure - DOWNLINK

Frame number ( DOWN LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

FCCH - Frequency correction Channel SCH - Synchronisation ChannelBCCH - Broadcast Control ChannelAGCH - Access Grant Chan PCH - Paging Channel

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

F S B B B B A A A A F S P P P P P P P P F S

F S F S I

0123

0123

Timeslots

BCH & CCCH - 51 Frame structure - UPLINK

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

R A C H

R A C H

R A C H

R A C H

Frame number ( UP LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0

12

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

0

12

RACH - Random Access Channel ( A short burst is transmitted by mobile towards BTS on RACH)

Timeslots

DCCH - Dedicated Control Channels Dedicated Control Channels have a TCH like allocation.

DCCH have three Sub Channels. SDCCH - Standalone Dedicated Control Channel This

is used as an interim channel before final assignment of TCH. SDCCH is used for signalling and Authentication message transfers.

FACCH - Fast Associated Control Channel . FACCH is used by BTS to command a handoff to the mobile. A TCH frame is used up by FACCH , since handoff has to take place on priority.

SACCH - Slow Associated Control Channel - SACCH flows at a slower rate on Uplink & Downlink along with TCH or SDCCH. During a call, SACCH flows once for every 24 Frames of TCH .

SDCCH - Stand-alone Dedicated Control CHannel

USED DURING CALL SET-UP

Stepping Stone between BCH and TCH

Used for Authentication Etc.

SDCCHSDCCH

TCH

BCH BCH BCH

DOWNLINK ( BTS - MS )–Mobile Tx Power Commands –Mobile Timing Advance–Cell's Channel Configuration

UPLINK ( MS - BTS )–Received signal quality report (RXQual)

–Received signal level report (RXLev)–Adjacent BCH power measurements –Mobile's status

SACCH - Slow Associated Control CHannel

INTERRUPTS TCH ON UPLINK AND DOWNLINK

Rapid message exchange for handovers Control Bits either side of midamble:

–Indicate TCH ( 0 ) or FACCH ( 1 )

FACCH - Fast Associated Control CHannel

Miidamble

8.25bits

357 bits

126 bits

157 bits

3

GuardPeriod

Data

Tail bits Data

Controlbit

Tail bit

Controlbit

SDCCH - Combined Channel Config ( Shares Time slot 0 with BCH and CCCH )

Frame number ( DOWN LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Time

slots

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

F S B B B B A A A A F S P P P P P P P P F S D D D D

D D D D F S D D D D D D D D F S H H H H H H H H I

SDCCH ( D ) : Standalone Dedicated Control ChannelSACCH ( H ) : Slow Associated Control Channel

0123

0123

BCH & CCCH - 51 Frame structure - UPLINK

SDCCH

SDCCH

SDCCH

SDCCH

RACH

RACH

SAC

CH

SACC

H

SACC

H

SACC

H

SACC

H

SACC

H

SACC

H

SACC

H

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

R A C H

R A C H

R A C H

R A C H

Frame number ( UP LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0

12

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

RACH

RACH

SDCCH

SDCCH

SDCCH

SDCCH

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

0

12

RACH - Random Access Channel ( A short burst is transmitted by mobile towards BTS on RACH)

Timeslots

8.25bits357

bits126

bits157 bits

3

GuardPeriod

Data

Tail bits Data

Controlbit

Midamble

Tail bit

Controlbit

TCH - Traffic Channel

One time burst

Traffic Channel carries the Voice data. Two blocks of 57 bits contain voice data . One TCH is allocated for every active call. While call is in

progress if there is degradation in quality of current channel, BTS may shift the communication to another TCH on a different Carrier and/or Time slot .

A Full rate TCH carries 13 KB/s voice data , and Half rate TCH carries a 6.5 KB/s voice data.

156.25 bits or 576.92 uS

TCH Multiframe - TCH Full rate

26 Frames - 120 ms24 Carry Speech, 1 Idle, 1 SACCH

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

T T A -T T T T T T T T T T T T T T T T T T T T T T

SACCH Idle

TCH Multiframe - TCH Half rate

26 Frames - 120 ms

24 Carry Speech , 2 SACCH ( shared by two mobiles - a & b )

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Ta Tb Aa AbTa Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb

SACCH-a SACCH-b

Click here to type bulleted textF S B B B B A A A A A A A A F S P P P P D D D D D D

T T T T T T T T T T T T

SA T T T T T T T T T T T T Idle

T T T T T T T T T T T T SA T T T T T T T T T T T T Idle


T T T T T T T T T T T T SA T T T T T T T T T T T Idle




Frame number 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0

1

2

3

4

5

6

7

T - TCH SA - SACCH I - Idle

A delay of (12 * 8)+1 Timeslotsis kept between two successiveSACCH .

TCH and SACCH - FRAMES

TimeSlots

H GSM Course

FRAMES

00

11

22

4823

4924

5025

= 6.12 sec

1 Superframe = 51 x 26 CCH MF = 1326 TF = 26 x 51 TCH MF = 1326 TF

1 Burst = 577usecs

0 1 2 3 4 5 6 71 TDMA Frame = 8 bursts = 4.616 ms

0 1 2 23

24

25

0 1 2 48

49

50

Multiframe

1 TCH Multiframe = 26 TF = 120ms

1 CCH Multiframe = 51 TF = 234.6ms

0 1 2 3 2044

2045

2046

20471 Hyperframe = 2048 Superframes = 2715648 TDMA

Frames = 3 hrs 28 min 53 sec 760 ms

TDMA approach requires signals to arrive at BTS atthe correct time. They must not overlap.

BTS

Timing Advance

H

Timing Advance

TB

Synch Seq 41 bits

Encrypted bits 36

TB

Guard Period 68.25 bp63

bitsTiming Adv

5.25 GP

BSS calculates access delay from RACH in terms of bits

Informs Mobile to delay its timing in terms of bits

Maximum Timing Advance of 63 bits

RACH Burst

H

Mobile Maximum Range

Range = Timing Advance x bit period x velocity2

Range = Distance between Mobile to Base StationTiming Advance = Delay of Bits ( 0 -- 63 )Bit period = 577 / 156.25 = 3.693 usecs = 3.693 x 10e-6 secsVelocity = 3 x 10e5

Range = ( 63 ) x ( 3.693 x 10e-6 ) x (3 x 10e5) 2

= 34.9 kms

Hopping Traffic Channel

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

C1

C2

C3

C1

C2

C3

UPLINK

ADJACENT CELLBCH

DOWNLINK

IREG• PURPOSE: To test various call scenarios to provide reliable Roaming services• Various Call Scenarios

•Mobile to Mobile•PSTN to Mobile•Checking Announcements•Call Forwarding•SMS Test•Combined Test

H

Mobile Searches for Broadcast Channels (BCH)

Synchronises Frequency and Timing

Decodes BCH sub-channels (BCCH)

Checks if Network Allowed by SIM

Location Update

Authentication

Mobile Turn-On

BSC

MSC

Location Area 1

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BSC

BSC

Location Area 3

Location Area 2

Location Area

MCC MNC LAC

Location Area Identity

H

IMPORTANCE OF LOCATION AREA

Reduce Paging Load

Resource Planning

L.Area = 1

L.Area = 2

L.Area = 3

H

What is Location Update MSC should know the Location of the Mobile for paging.

Mobile is continously changing Location Area. Mobile when changes Location Area informs the MSC about its new

L.A

Process of informing MSC about new Location Area is Location Update

L.Area = 1 L.Area = 2 L.Area = 3

Location Update

H

IMSI ATTACH

Mobile turns off and sends an IMSI Detach to MSC.

Mobile turns on again and compares LAI.

If same,sends an IMSI attach to MSC.

1. Normal Location Update.

2. IMSI Attach.

3. Periodic Location Update.

Types of Location Update

H

NORMAL LOCATION UPDATE

Mobile turns on power.

Reads the new LAI.

If different,does a Location Update.

H

PERIODIC LOCATION UPDATE

Mobile enters non-coverage zone.

MSC goes on sending Pages

Mobile has to inform MSC after a set period.

H

Location Update Mobile Changes Location Area

Reads the new Location Area from BCCH

Sends a RACH ( request for channel )

Gets a SDCCH on AGCH

Sends its IMSI and new & old LAI in a Location Update Request to MSC on SDCCH

MSC starts Authentication

If successful, Updates the new Location area for the Mobile in the VLR

Sends a confirmation to the Mobile

Mobiles leaves SDCCH , and comes to idle mode

H

Mobile Originated Call

Channel Request

Immediate Assign

Service Request

Authentication

Set Up

Ciphering

Call Proceeding

Assignment

Alerting

Connection

H

MOBILE TERMINATED CALL

Channel Request

Immediate Assign

Authentication

Set Up

Ciphering

Call Confirmed

Assignment

Alerting

Connection

Paging

Paging Response

H

Security Features

Authentication

--- Process to verify the Authenticity of SIM--- Mobile is asked to perform an operation using an identity unique to SIM.

Ciphering

--- Process of coding speech for secrecy--- The speech bits are EXORed with bit stream unique to MS

H

Security FeaturesTMSI Reallocation

Loc Upd ( IMSI )

TMSI Allocation

Call Setup ( TMSI )

TMSI Reallocation

H

Security FeaturesIdentity Check

Identity Check ( IMEI )

Sends IMEI

EIRWhite listed / Grey listed / Black listed ?????

H

HANDOVER

Cell 1

Cell 2

--- Handover is a process by which the control/communication of a Mobile is transferred from one cell to another

H

CRITERIA FOR HANDOVER

Receive Quality (RXQUAL) on Uplink & Downlink.

Receive Signal Strength (RXLEV) on Uplink & Downlink.

Distance ( Timing Advance ).

Interference Level.

Power Budget.

H

Handover Decision

BSC processes the measurement reported by Mobile and the BTS.

BSS performs averaging function on these measurements every SACCH frame ( 480ms).

Handover Decision algorithm is activated after a set number of SACCH frame periods by comparison against Thresholds.

H

TYPES OF HANDOVERS

INTRA - CELL HANDOVER

INTER - CELL HANDOVER

INTRA - BSC HANDOVER

INTER - BSC HANDOVER

INTER - MSC HANDOVER

H

INTRA - CELL HANDOVER

- Handover between channels / timeslots of same cell

BTS

H

INTER - CELL HANDOVER

--- Handover between cells of same BTS

C0 C

0

BTS

H

INTRA - BSC HANDOVER

MSC BSC

BTS

BTS

--- This type of Handover takes place if the cell to which which handover is to be done belongs to the sameBSC. --- In this the BSC handles everything without involving MSC.--- The MSC will be informed by the BSC after Handover.

H

INTER BSC HANDOVER

MSC

BSC

BSC

BTS

BTS

--- In this type of Handover,the Mobile is handed over to a cell which belongs to another BSC.--- The MSC is completely involved in this Handover

H

GMSC

MSC BSC BTS

MSC BSC BTS

--- If the cell belongs to another MSC,then it is Inter-MSC handover. --- In this case the handover takes place through the interconnecting element (PSTN) between the MSC's

INTER - MSC HANDOVER

H

WHAT IS CELL BARRING ?

BTS

H

Every Mobile has an access class .

Every cell defines the Mobile classes which are barred access.

Cell Barring

USE OF CELL BARRING

--- Reserving Cells for Handovers.

--- Reserving Cells for a certain Mobile Class.

H

Both users talk alternately.

Each direction of Transmission is only 50 %

Transmitter is switched ON for useful information frames.

What is DTX ?

H

Need for DTX

---- To increase Battery Life

---- To reduce the average interference level

DTX is done by DTX Handlers which have the following functions.

H

Voice Activity Detector ( VAD )

Senses for speech in 20ms blocks Removes stationary noise.

VAD is an energy detector.

Compares Energy of filtered speech threshold

H

Evaluation of Background noise

Background noise is always present with speech.

DTX cuts off this noise with speech.

Gives an uncomfortable feeling to the listener.

VAD takes care by inserting comfort noise.

H

CELL BROADCAST

Message is continously broadcasted in cell/or cells

Broadcast is done on SDCCH

BCCH informs the mobile the details of SDCCH for CBCH

Mobile tunes to SDCCH at certain intervals and reads messages

All Mobiles dont support this feature

H

Short Message Service

SMSCentre

MSC/VLR

BSC BTS

Short Message is sent to a particular Mobile Station

H

Emergency Calls

-- GSM Specs define ' 112' as emergency number

-- '112' is accessible with or without SIM

-- Without SIM it is sent on the best channel

-- Mobile on sensing '112' sets the establishment cause to emergency call in the RACH

-- Routing of this call can be done to a desired location defined in the Switch.

H

GSM Phase 2 features

Extended Frequency Band ( 50 more channels )

Multiple and Alternate Ciphering Algorithm

Half - Rate Coding

Compatibility with DCS 1800 Specifications

Enhancement of SMS and SIM functions

Additional functions for bearer services

H

GSM Phase 2 + features

Data transmission at 64 Kbps and above

DECT access to GSM

PMR/ Public Access Mobile Radio ( PAMR ) - like capabilities

GSM in the local loop

Packet Radio

SIM enhancements

Premium rate services ( e.g. Stock prices sent to your phone )

H

Automatic National Roaming

PLMN "A"

PLMN "B"

PLMN "D" PLMN "C"

STP

Roamer from "A"

H

Automatic International Roaming

PLMN "A"

PLMN "Z"

CountryInterntlGateway

InterntlGateway

CountryInterntlGateway

Gsm basics

Business

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