GSM (GLOBAL SYSTEM FOR MOBILE COMMUNICATION)

It all started like this First telephone (photophone) – Alexander Bell, 1880 First telephone (photophone) – Alexander Bell, 1880 The first car mounted radio The first car mounted radio telephone – 1921 telephone – 1921

But what’s cellular? HLR, VLR, AC, EIR MSC PSTN BS

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

GSM: History Developed by Group Spéciale Mobile (founded 1982) which was an initiative of CEPT ( Conference of European Post and Telecommunication ) Aim : to replace the incompatible analog system Presently the responsibility of GSM standardization resides with special mobile group under ETSI ( European telecommunication Standards Institute ) Full set of specifications phase-I became available in 1990 Under ETSI, GSM is named as “ Global System for Mobile communication “ Today many providers all over the world use GSM (more than 135 countries in Asia, Africa, Europe, Australia, America) More than 1300 million subscribers in world and 45 million subscriber in India.

Tele Services Telecommunication services that enable voice communication via mobile phones Offered services - Mobile telephony - Emergency calling

GSM Overview

1st Generation Start to use in 1989 Call forwarding All calls No answer Engaged Unreachable Outgoing calls barring Incoming calls barring Global roaming

2nd Generation Finished process in 1995 SMS(Short Message Services) Multi Party Calling Call holding Call waiting Mobile data service Mobile fax service Call line identity Advice of charging Advice of charging Cell broadcast Cell broadcast

2+ Generation Start to use in 1998 Start to use in 1998 Services developed Services developed DECT and GSM DECT and GSM VPN(Virtual Private Network) VPN(Virtual Private Network) Packet Radio Packet Radio SIM development SIM development Enjoyable services Enjoyable services

GSM in World

GSM in India

GSM System Architecture BSC MSC MS BTS GMSC PSTN ISDN PDN EIR AUC HLR VLR

Outgoing Call 1. MS sends dialled number to BSS 2. BSS sends dialled number to MSC 3,4 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 GMSC 6 GMSC routes the call to local exchange of called user 7, 8, 9,10 Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS

Incoming Call 1. Calling a GSM subscribers 2. Forwarding call to GSMC 3. Signal Setup to HLR Request MSRN from VLR 6. Forward responsible MSC to GMSC 7. Forward Call to current MSC Get current status of MS Paging of MS MS answers Security checks Set up connection

Handovers Between 1 and 2 – Inter BTS / Intra BSC Between 1 and 2 – Inter BTS / Intra BSC Between 1 and 3 – Between 1 and 3 – Inter BSC/ Intra MSC Inter BSC/ Intra MSC Between 1 and 4 – Between 1 and 4 – Inter MSC Inter MSC

Authentication in GSM

Key generation and Encryption

Mobile Radio Cellular Mobile Communications

Mobile Comms. Principles –Mobile uses a separate, temporary radio channel to talk to the cell site –Cell site talks to many mobiles at once, using one channel per mobile –Channels use a pair of frequencies for communication The forward link for transmitting from the cell site The forward link for transmitting from the cell site The reverse link for the cell site to receive calls from the users The reverse link for the cell site to receive calls from the users

Mobile Comms. Principles Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications Basic structure of mobile networks includes telephone systems and radio services Basic structure of mobile networks includes telephone systems and radio services

Mobile Comms. Principles Where mobile radio service operates in a closed network and has no access to the telephone system, mobile telephone service allows interconnection to the telephone network Where mobile radio service operates in a closed network and has no access to the telephone system, mobile telephone service allows interconnection to the telephone network

Mobile Comms. Principles Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications basic structure of mobile networks includes telephone systems and radio services basic structure of mobile networks includes telephone systems and radio services

Mobile Systems Using Cells The cellular concept employs variable low- power levels The cellular concept employs variable low- power levels –cells are sized according to the subscriber density and demand in a given area Cells can be added to accommodate population growth Cells can be added to accommodate population growth

Cellular System Architecture In modern cellular telephony, rural and urban regions are divided into areas according to specific provisioning guidelines In modern cellular telephony, rural and urban regions are divided into areas according to specific provisioning guidelines Deployment parameters, such as amount of cell-splitting and cell sizes, are determined by engineers experienced in cellular system architecture Deployment parameters, such as amount of cell-splitting and cell sizes, are determined by engineers experienced in cellular system architecture

Cells A cell is the basic geographic unit of a cellular system A cell is the basic geographic unit of a cellular system –The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided –Cells are base stations transmitting over small geographic areas that are represented as hexagons –Size varies depending on the landscape

GSM Operation Speech decoding Channel decoding De-interleaving Burst Formatting De-ciphering DemodulationModulation Ciphering Burst Formatting Interleaving Channel Coding Speech coding Radio Interface Speech 13 Kbps 22.8 Kbps 33.6 Kbps Kbps

GSM-Frame Structure

OPEN INTERFACES OF GSM Network Switching Subsystem(NSS) Network Switching Subsystem(NSS) Base Station Subsystem(BSS) Base Station Subsystem(BSS) Network Management Subsystem(NMS) or Operation and Support Subsystem(OSS) Network Management Subsystem(NMS) or Operation and Support Subsystem(OSS) They connect with Air,A,O&M interfaces They connect with Air,A,O&M interfaces

PROCEDURE OF CALL SET UP FROM MOBİLE USER

SIGNALS AND PROTOCOLS STANDART MESSAGES STANDART MESSAGES SENDER WANTS TO SERVICE SENDER WANTS TO SERVICE OPERATOR ASK THAT YOU WANTS TO TALK,BUT WHICH USER OPERATOR ASK THAT YOU WANTS TO TALK,BUT WHICH USER OPERATOR CONNECT TO RECEIVER OPERATOR CONNECT TO RECEIVER WHEN THE RECEIVER REPLIES TO CALL,THE CALL STARTS WHEN THE RECEIVER REPLIES TO CALL,THE CALL STARTS WHEN THE RECEIVER OR SENDER CLOSE THE PHONE, THE OPERATOR FINISH CONNECTION TO EACH OTHER WHEN THE RECEIVER OR SENDER CLOSE THE PHONE, THE OPERATOR FINISH CONNECTION TO EACH OTHER

PROCEDURE OF SIGNALS

COMMON CHANNEL SIGNALLING SYSTEM MTP(MASSAGE TRANSFER PART) MTP(MASSAGE TRANSFER PART) TUP(TELEPHONE USER PART) TUP(TELEPHONE USER PART) SSCP(SIGNALLING CONNECTION AND CONTROL PART) SSCP(SIGNALLING CONNECTION AND CONTROL PART)