Mobile Communication System - Global system for mobile communication - GSM - is a 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 mobile telephones (mobile stations), base stations (cell sites), and switching systems.

Digital Media Formats - GSM is designed to transfer digital information. The initial version of GSM transmitted digital media in circuit switched (continuous transmission) form and later versions of GSM deliver data in packet data form.

Functional Sections - GSM system is composed of three key sections:
- Mobile Stations (MS) - A device that converts media to and from GSM radio signals.
- Base Station Subsystem (BSS) - Assemblies that convert digital signals to radio signals that can be sent to mobile devices and receive radio signals that can be converted back to their digital form. The BSS is divided into base station - BS - parts that are located at the cell site and base station controllers - BSC - that coordinate the distribution and reception of communication connections.
- Network and Switching System (NSS) - The NSS performs the interconnection between the base station parts and other networks such as the public switched telephone network - PSTN - and public Internet. The NSS is composed of circuit data and packet data switches, databases, and administrative control services.