What is GSM?

§GSM, the Global System for Mobile Communications, is a digital cellular communications system

§

§GSM provides –

§Digital Transmission

§ISDN compatibility

§Worldwide roaming in other GSM networks

§Provides a model for 3G Cellular systems (UMTS) 

Nomenclature

nMS (Mobile Station) = ME (Mobile Equipment ) +SIM (Subscriber Identity Module)

nBSS (Base Station Subsystem) = BTS (Base Transceiver Station) + BSC (Base Station Controller)

nNSS (Network Switching Subsystem)

nMSC (Mobile Switching Center): telephony switching function and authentication of user

GSM Protocol Stack

-In any telecommunication system, signalling is required to coordinate the necessarily distributed functional entities of the network.

-The transfer of signalling information in GSM follows the layered OSI model

nLayer 1: Physical Layer

nRadio Transmission

nLayer 2: Data Link Layer (DLL)

nprovides error-free transmission between adjacent entities, based on the ISDN’s LAPD protocol for the Um and Abis interfaces, and on SS7’s Message Transfer Protocol (MTP) for the other Layer interfaces

nLayer 3: Networking or Messaging Layer

nResponsible for the communication of network resources, mobility, code format and call-related management messages between various network entities