GSM represents the Global System for Mobile communication. It is a standard established by the European Telecommunication Standards Institute (ETSI) to define protocols for second-generation (2G) digital mobile networks. It was restored for the first generation (1G) mobile networks. The concept of producing GSM was introduced from a mobile-based mobile radio framework at the Bell Laboratories in the early 1970s.
The GSM standard works on three multiple carrier frequencies: the 900 MHz band, which was utilized by the initial GSM system. The 1800 MHz band, which was inserted to provide the multiple subscribers and the 1900 MHz frequency, is used generally in the U.S.
The GSM specifications represent the functions and interface needed but do not address hardware.
The GSM system is split into three major systems including the switching framework, the base station framework, and the operating support framework.
The switching system is answerable for implementing call processing and subscriberrelated services. It contains the following functional units −
The Home Location Register (HLR) is a database used for the storage and administration of subscriptions. The HLR is the most significant database as it saves permanent records about subscribers, such as a subscriber’s service profile, location data, and activity status.
The mobile service switching center (MSC) implements the telephony switching services of the system. It also implements such services as toll ticketing, network interfacing, common channel signaling, etc.
The visitor location register (VLR) is a database that includes temporary data about subscribers that are required by the MSC to service visiting subscribers.
The equipment identity register (EIR) is a database that includes data about the identity of cellular equipment that avoids calls from robbed, unauthorized, or inadequate mobile stations.
All radio-related services are implemented in the BSS which includes the base station controller (BSCs) and the base transceiver stations (BTSs).
The BSC supports all the control functions and physical connections between MSC and BTS. It is a high-capacity switch that supports functions including handover, mobile configuration record, and control of radio frequency power levels in base transceiver stations.
The BTS manages the radio interface to the cellular station. The BTS is the radio equipment required to service each cell in the system.
The operation and maintenance center (OMC) is linked to all equipment in the switching framework and the BSC. The performance of OMC is known as the operation and support system.
The OSS is the functional body from which the network operator audits and controls the system. The goal of OSS is to provide the user economical support for centralized, regional, and local operational and maintenance activities that are needed for a GSM system.