The GSM (Global System For Mobile Communication

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Chapter 2 Background 2.1 GSM TECHNOLOGY GSM (Global System for Mobile Communications) is a standard which was developed by the European Telecommunications Standards Institute. Basically the second generation (2G) digital cellular networks protocols for mobile phones are described by GSM. GSM has a network of around 219 countries and territories with total 90% market share in mobile communications globally. The GSM standard came after first generation (1 G) as its replacement. 1G used analog cellular networks whereas 2G originally focused on digitally switched networks. Full duplex telephony was hence provided. This was further replaced by circuit switched network of transport and later packet transport system like general packet radio service. 2.1.1 GSM ARCHITECTURE Figure 1: GSM architecture 2.1.1.1 BASE TRANSCEIVER STATION A mobile station is first connected to a base transceiver station. A BTS is a tower (network equipment) which is used for communication between the entire network and the mobile. There are facilities of encryption and deciphering, transceiver and antennas, and equipments for spectrum filtering. A BTS can serve many sectors as well as cell’s numerous frequencies due to the multiple transceivers attached to it. BTS are also known as base stations or cell sites. 2.1.1.2 BASE STATION CONTROLLER A base station controller works like load sharing equipment. Many BSCs are attached to the BTS. The BSC effectively reduces the load on the MSC as it itself monitors the numerous BSCs attached to it. It also performs managing of radio networks which involve radio frequency control. It is also helpful in providing hand over and calls setup. It helps in fulfilling capacity requirements and providing full mo... ... middle of paper ... ...ENTITIES 2.1.3.1 CELL GLOBAL IDENTITY Figure 6: CGI divisions Cell global identity consists of 4 units – MCC, MNC, LAC and CI. MCC refers to Mobile Country Code. MNC is Mobile Network Code. LAC refers to Location Area Code and CI is Cell Identity. The Mobile Subscriber Integrated Services for Digital Network (MSISDN) number is the telephone number of the Mobile station. This is the number which the calling party has to dial to reach a particular subscriber. 2.1.3.2 SUBSCRIBER IDENTIFICATION 2.1.3.2.1 INTERNATIONAL MOBILE SUBSCRIBER IDENTITY IMSI – International Mobile Subscriber Identity is defined within a RAN – Radio access Network. It is elemental in identifying the mobile subscriber. The International Mobile Subscriber Identity (IMSI) is fixed for a particular subscriber and it stores the primary identity of the subscriber within a mobile network.
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