GSM Vs CDMA - A Comparative Study

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GSM Architecture

A GSM based PLMN 16 (Public Land Mobile Network) can be broadly divided into 3 parts: • The Mobile Station • The Base Station Subsystem, and • The Network Subsystem The Mobile Station The Mobile Station (MS) refers to the user end of the network. It consists of the GSM device (cellphone) and the SIM (Subscriber Identity Module). Each mobile device has a globally unique IMEI (International Mobile Equipment Identity) and each SIM has an IMSI (International Mobile Subscriber Identity), which is used to identify and allow the subscriber to use various services. The SIM card may be protected against unauthorized use by using a PIN (Personal Identity Number).

The Base Station Subsystem (BSS)

Mobile networks consist of many BTS (Base Transceiver Stations), each of which covers a certain geographical area. This area is called a 'cell.' The BTSs are responsible for directly communicating with the mobile devices. Several BTSs are controlled together by a BSC (Base Station Controller). The BSC provides connectivity to the network subsystem.

The Network Subsystem

The MSC (Mobile services Switching Center) is the central component of the network subsystem. It communicates with all the BSCs and is responsible for providing all the functionalities to mobile devices like registration, authentication, call routing etc. Usually, a network also has a GMSC (Gateway MSC) to communicate with external (landline) networks like ISDN and PSTN ¹⁷(public switched telephone network).

The network subsystem also maintains many registers which contain information necessary for the smooth functioning of the network. The HLR (Home Location Register) stores information about the current location of all subscribers of the network. This information is necessary for routing calls or messages to their intended destinations. A VLR (Visitor Location Register) covers one or more cells and stores information about the subscribers currently under its area of influence. The EIR (Equipment Identity Register) authenticates and stores equipment data. The AUC or AC (Authentication Center) stores and validates each user's PIN. The MSC communicates with these registers whenever it needs information.

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16] The entire set of cells served by one network operator. It refers to the entire area in which an operator offers radio coverage and access.
17] Also referred to as the Plain Old Telephone System, it is a collection of interconnected voice-oriented public telephone networks, both commercial and government owned.

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