Global system for mobile communication (GSM) is wide area wireless communications system that uses digital radio transmission to provide voice, data, and multimedia communication services. A GSM system coordinates the communication between a mobile telephones (mobile stations), base stations (cell sites), and switching systems. Each GSM radio channel is 200 kHz wide channels that are further divided into frames that hold 8 time slots. GSM was originally named Groupe Special Mobile. The GSM system includes mobile telephones (mobile stations), radio towers (base stations), and interconnecting switching systems. The GSM system allows up to 8 to 16 voice users to share each radio channel and there may be several radio channels per radio transmission site (cell site).

Figure 1.1 shows an overview of a GSM radio system. This diagram shows that the GSM system includes mobile communication devices that communicate through base stations (BS) and a mobile switching center (MSC) to connect to other mobile telephones, public telephones, or to the Internet. This diagram shows that the MSC connects to databases of customers. This example shows that the GSM system mobile devices can include mobile telephones or data communication devices such as laptop computers.

Figure 1.1: Global System for Mobile Communications (GSM)

The GSM specification was initially created to provide a single industry standard for European cellular systems. In 1982, the development of the GSM specification began and the first commercial GSM system began operation in 1991. In 2004, there were more than 1.046 billion GSM subscribers in 205 countries and...