GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones. It is the de facto global standard for mobile communications with over 90% market share, and is available in over 219 countries and territories

 

 

The GSM standard was developed as a replacement for first generation (1G) analog cellular networks, and originally described a digital, circuit-switched network optimized for full duplex voice telephony. This was expanded over time to include data communications, first by circuit-switched transport, then packet data transport via GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution or EGPRS).

The Global System for Mobile Communications (GSM) is the most deployed wireless network for cellular mobile telephony in the world. The ubiquity of GSM makes possible the international roaming and enables subscribers to use the GSM network for phone calls and data communication while travelling between countries. GSM is considered to be a second generation (2G) mobile phone system, since it was the first mobile phone protocol that employed digital signalling and speech channels. GSM networks operate mostly in the 900 MHz or 1800 MHz bands. 

 

 

 

The network is structured into a number of discrete sections:

• Base Station Subsystem – the base stations and their controllers explained
• Network and Switching Subsystem – the part of the network most similar to a fixed network, sometimes just called the "core network"
• GPRS Core Network – the optional part which allows packet-based Internet connections
• Operations support system (OSS) – network maintenance

 

 

 

 

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