GSM Overview
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GSM Overview. Manish singh. OBJECTIVES. Describe the Cellular Concept Explain the GSM Access Network Explain the GSM Core Network Explain the GPRS Core Network. Inter-Exchange Junction. Subscriber Line (2W). BSC. BTS. MS. Telephone Exchange. Mobile Switching Centre (MSC).

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Gsm overview

GSM Overview

Manish singh


Gsm overview

OBJECTIVES

  • Describe the Cellular Concept

  • Explain the GSM Access Network

  • Explain the GSM Core Network

  • Explain the GPRS Core Network


Communication mobile

Inter-Exchange

Junction

Subscriber

Line

(2W)

BSC

BTS

MS

Telephone

Exchange

Mobile Switching

Centre (MSC)

Communication - Mobile


Gsm overview

CELLULARMOBILECONCEPTS

WHAT IS A CELL ?

  • A base station (transmitter) having a number of

  • RF channels is called a cell

  • Each cell covers a a limited number of mobile

  • subscribers within the cell boundaries

  • ( Coverage area)

  • Typical Cell Radius Aprrox = 30 Km

  • (Start up), 1 KM (Mature)


Gsm overview

Voice

Channels

Coverage

area

Forward path

Reverse path

Or

control

channels

MS

Lines to

BSC

A RADIO CELL


Fundamental problems

Large no. of subscribers in the range of millions

Fundamental problems

  • Radio range, or coverage

  • No. of channels, or voice circuits

  • Full, seamless service coverage


Gsm overview

GSM Specifications

Carrier Separation -200 kHz

Duplex Distance -45 MHz

No. of RF Carriers -124

Access Method -TDMA/FDMA

Modulation Method -GMSK

Transmission Rate -270.833 Kbps

Speech Coding -Full rate 13 Kbps

Half rate 6.5 Kbps


Gsm fdma f requency d ivision m ultiple a ccess

890

915

935

960

25 MHz

25 MHz

1

2

1

2

0

0

Mobile to Base

Base to Mobile

(MHz)

890.4

890.6

935.4

935.6

890.2

935.2

200 kHz

200 kHz

45MHz

Channel layout and frequency bands of operation

GSMFDMA(Frequency Division Multiple Access


Gsm tdma t ime d ivision m ultiple a ccess

8

8

7

7

6

6

5

5

4

4

3

3

2

2

1

1

GSMTDMA(Time Division Multiple Access)

Amplitude

45 MHz

Frequency

F1

(Cell Rx)

F2

F2’

F1’

(Cell transmit)

Typical TDMA/ FDMA frame structure


Fdma tdma scheme

TIME

BP2

BP1

BP8

BURST

BP7

BP6

BP5

BP4

BP3

BP2

BP1

FREQ

MHz

890.2

890.6

891.0

915.8

890.0

890.4

890.8

891.2

FDMA/TDMA Scheme

F

R

A

M

E


Gsm overview

GSM RF CHANNELS

LOGICAL CHANNELS

USER INFORMATION( TRAFFIC)

SIGNALLING INFORMATION (CONTROL)


Gsm overview

OPERATIONAL CONCEPTS

  • Subscribers are not allocated dedicated channels

  • TCH Allocated to users only when needed

  • Hence IDLE MODE & DEDICATED MODE

  • DEDICATED MODE

-- When a full Bi -directional P to P CHL

has been allocated during an established call

  • IDLE MODE MODE

-- When MS is powered on (active)

without being in dedicated mode


Network architecture

B

T

S

B

T

S

MSC VLR

B

T

S

MSC VLR

Network Architecture

1 MSC=16 BSC

1 BSC=1024 TRU

OSS

(

HLR

PSTN

ISDN

Data

Networks

BSC

A Interface

A-bis interface

Air interface


Gsm network structure

GSM Service Area:Total area served by the combination of all member countries where a mobile can be served.

PLMN Service Area:It is one N/W area.

MSC Service Area:There can many MSC/VLR in one PLMN area.It is one Mobile Exch. Area.

GMSC:All I/C calls for PLMN N/W will be routed through GMSC. In a GSM/PLMN N/W all mobile terminated calls will be routed to a Gateway MSC. Call connections between PLMNs , or to fixed N/Ws must be routed to a GMSC.The GMSC contains the Inter working functions to make these connections.

Location Area

Cells

GSM Network Structure


Gsm overview

GSM Network Structure

LOCATION AREA :There are several LA in a MSC/VLR combination. A LA is a part of the MSC/VLR service area in which a MS may move freely without updating location information to the MSC/VLR exchange that control the LA. Within a LA a paging message is broadcast in order to find the called mobile subs. LA can be identified by system using the LAI.

CELL :A cell is an identity served by one BTS. The MS distinguishes between cells using the BASE STATION IDENTIFICATION CODE(BSIC) that the cell site broadcast over the air.


Gsm overview

MSC/VLR

MSC/VLR

MSC/VLR

MSC/VLR

I

II

IV

III

GSMPLMN Service Area


Gsm overview

MSC/VLR

LA 2

LA 1

LA 3

LA 6

LA 4

LA 5

GSMMSC Service Area


Gsm overview

MSC/VLR

GSMCells

C1

LA 3

LA 2

LA 1

C2

C6

C4

C5

C3

C7

LA 6

LA 4

LA 5

C = Cell


Gsm relation between areas in gsm

Location Area

Cell

Area served by a BTS

Location Area

MSC Service Area

PLMN Service Area

GSM Service Area

GSMRelation between areas in GSM


Gsm functions of mobile station

Voice and data transmission

Frequency and time synchronization

Monitoring of power and signal quality of the surrounding cells

Provision of location updates even during inactive state

Equalization of multi path distortions

GSMFunctions of Mobile Station


Gsm mobile station

Portable, vehicle mounted, hand held

MS identified by unique IMEI(International Mobile Equipment Identity)

Shall display at least last ten received, dialled and missed calls

Minimum talk time of 1hr 30 min. and standby time of 80 hrs

160 characters long SMS

GSMMobile Station


Gsm mobile identification numbers

IMEI

MSISDN

IMSI

GSMMobile Identification Numbers


Gsm imsi

International mobile subscriber’s Identity

The IMSI is an unique identity which is used internationally and used within the network to identify the mobile subscribers.

The IMSI is stored on the subscriber identity module (SIM), the HLR, VLR and AC database.

GSMIMSI


Gsm overview

MSC/VLR

BSC

BSC

BSC

n BTS

n BTS

RADIO SUB SYSTEM (RSS)

RSS


Gsm function of bts i

Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna

Transcoding and rate adaption Functionality

Time and frequency synchronisation signals transmission.

GSMFUNCTION OF BTS -I


Gsm function of bts ii

Frequency hopping

Random access detection

Uplink radio channel measurements

BTS mainly consists of a set of transceivers (TRX).

GSMFUNCTION OF BTS -II


Gsm functions of bsc i

It is connected to BTS and offloads MSC

Radio resource management

Inter-cell handover

Reallocation of frequencies

Power control

GSMFUNCTIONS OF BSC-I


Gsm functions of bsc ii

Time delay measurement of the received signals from MS with respect to BTS clock.

Performs traffic concentration to reduce the number of lines from BSC to MSC.

GSMFUNCTIONS OF BSC-II


Gsm msc bss configurations

BTS

BSS

BTS

BTS

BTS

BTS

BTS

MSC

BTS

BSC

GSMMSC-BSS Configurations

Multi - cell site (sector Cells

Configuration -5

A

A

Single - cell site

Configuration -1

A

Many single cell sites

BSS

A-bis

A-bis

Multi - cell site = multi--BTS site

Configuration -6

MCC: Mobile Switching Centre

BSS: Base Station System

BSC: Base Station Controller

BTS: Base Transceiver Station


Gsm msc mobile switching centre

Manages communication between GSM & other network

Call setup functions, basic switching are done

MSC takes into account the RR allocation in addition to normal exchange functions

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

GSMMSC ( MOBILE SWITCHING CENTRE)


Gsm msc functions i

Paging, specifically call handling

Location updation

Handover management

Billing for all subscribers based in its area

Reallocation of frequencies to BTSs in its area to meet heavy demands

GSMMSC Functions - I


Gsm msc functions ii

Echo canceller operation control

Signaling interface to databases like HLR,

VLR.

Gateway to SMS between SMS centers and

subscribers

Handle interworking function while

working as GMSC

GSMMSC Functions - II


Gsm visitor location register vlr i

It controls those mobiles roaming in its area.

VLR reduces the number of queries to HLR

One VLR may be incharge of one or more LA.

VLR is updated by HLR on entry of MS its area.

VLR assigns TMSI which keeps on changing.

IMSI detach and attach operation

GSMVISITOR LOCATION REGISTER (VLR)-I


Gsm data in vlr

IMSI & TMSI

MSISDN

MSRN.

Location Area

Supplementary service parameters

MS category

Authentication Key

GSMData in VLR


Gsm home location register hlr i

Reference store for subscriber’s parameters, numbers, authentication & Encryption values.

Current subscriber status and associated VLR.

Both VLR and HLR can be implemented in the same equipment in an MSC.

one PLMN may contain one or several HLR.

GSM Home Location Register(HLR)-I


Gsm home location register hlr ii

Data stored is changed only by man-machine.

IMSI, MS-ISDN number.

Category of MS ( whether pay phone or not )

Roaming restriction ( allowed or not ).

Supplementary services like call forwarding

GSM Home Location Register(HLR)-II

Permanent data in HLR


Gsm home location register hlr ii1

Temporary data in HLR

The data changes from call to call & is

dynamic

MSRN

RAND /SRES and Kc

VLR address, MSC address.

Messages waiting data used for SMS

GSM Home Location Register(HLR)-II


G eneral p acket r adio s ystem

General Packet Radio System

GPRS


Gsm overview

SMS-G/IW MSC

BSC

MSC/VLR

HLR

AUC

BTS

MS

EDGE

TRU

Iu

MS

MS

UMTS

R

N

C

BTS

U

T

R

A

N

BTS

R

N

C

BTS

Network Evolution

Gd

P

C

U

Gs

Gr

ISP

Network

Gb

SGSN

GGSN

Gi

Gn

Gn

CorporateNetwork

Backbone Network


Gsm overview

SMS-G/IW MSC

BSC

MSC/VLR

HLR

AUC

BTS

MS

EDGE

TRU

MS

Network Evolution

Gd

P

C

U

Gs

Gr

ISP

Network

Gb

SGSN

GGSN

Gi

Gn

Gn

CorporateNetwork

Backbone Network


Gsm overview

SMS-G/IW MSC

BSC

MSC/VLR

HLR

AUC

BTS

MS

EDGE

TRU

Iu

MS

MS

UMTS

R

N

C

BTS

U

T

R

A

N

BTS

R

N

C

BTS

Network Evolution

Gd

P

C

U

Gs

Gr

ISP

Network

Gb

SGSN

GGSN

Gi

Gn

Gn

CorporateNetwork

Backbone Network


Gprs architecture

GPRS Architecture

BTS

ISDN / PSTN / PLMN

Network

GMSC

MSC/VLR

Um

MT

Abis

EIR

A

BSC

Gs

AUC

Gf

TE

SGSN

MS

Gb

HLR

BSS

Gr

IP-Backbone

Network

Gn

AGSM Interface

AbisGSM Interface (Proprietary of M/s Ericsson)

AUCAuthentication Center

BSCBase Station Center

BSSBase Station System

BTSBase Transceiver Station

EIREquipment Identity Register

GGSNGateway GPRS Support Node

GMSCGateway Mobile services Switching Center

GxGPRS Interfaces

HLRHome Location Register

MSMobile Station

MSCMobile services Switching Center

MTMobile Terminal

SGSNServing GPRS Support Node

TETerminal Equipment

UmAir Interface

VLRVisitor Location Register

Gn

Gi

GGSN

External

IP Network

Gi

External

X.25 Network

GSM Network Elements

Signaling

GPRS Network Elements

Traffic & Signaling


Gprs components

To ensure the interworking of the PLMN, PDN and the wireless networks, two new major components are required.

These components are called GPRS Support Nodes.

There are two types of GPRS Support Nodes

Serving GPRS Support Node (SGSN)

Gateway GPRS Support Node (GGSN)

GPRS COMPONENTS


S erving g prs s upport n ode sgsn

An SGSN delivers packets to mobile stations within its service area. SGSNs send queries to Home Location Registers (HLRs) to obtain profile data of GPRS subscribers.

SGSNs detect new GPRS mobile stations in a given service area; and, finally, SGSNs process registration of new mobile subscribers and keep a record of their location inside a given service area.

Serving GPRS Support Node (SGSN)


G ateway g prs s upport n ode ggsn

GGSNs are used as interfaces to external PDNs. GGSNs maintain routing information that is necessary to tunnel the Protocol Data Units (PDUs) to the SGSNs that service particular mobile stations.

Other functions include network and subscriber screening and address mapping. One or more GGSNs may support multiple SGSNs.

Gateway GPRS Support Node(GGSN)


Gprs network enhancements

In addition to the new GPRS components, existing GSM and TDMA network elements must also be enhanced in order to support GPRS.

The following two pieces of equipment must be enhanced:

Base Station System (BSS): must be enhanced to recognize and send user data to the SGSN that is serving the area.

Home Location Register (HLR): must be enhanced to register GPRS user profiles and respond to queries originating from SGSNs regarding these profiles.

GPRS Network Enhancements


Advantages of gprs

Increased revenues by moving in to the mobile data market

Gain new subscribers requiring the data services without investing in to PCs to gain internet access

Retain current subscribers by offering new services

Reduce costs due to efficient use of network resources

Advantages of GPRS


Gsm overview

Thanks


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