GSM is an abbreviation of Global System for Mobile communications.
World's most of the mobile phone networks rely on GSM technology. GSM has become the world's fastest growing communications technology of all time and the leading global mobile standard, spanning 214 countries. GSM uses a variation of Time Division Multiple Access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA).
It is a digital cell-based communication service that started in Europe, and has quickly spread throughout most of the world. A notable exception is the US, where CDMA is the dominant standard; however, GSM is gaining popularity there. GSM is the most supported protocol in smartphones.
GSM was designed for circuit-switched voice communication. Circuitswitched means that fixed bandwidth is reserved for each direction of a phone call for the entire duration of the voice call, whether you are talking or not.
Although originally designed for voice, GSM now has a variety of higher bandwidth data services (e.g. GPRS and EDGE) available, running on top of the base GSM protocol. This allows for faster data transfer, as we will see shortly.
Types of GSM and band used in the frequency spectrum
- GSM 850
- GSM 900
- GSM 1800
- GSM 1900
The number indicates the frequency band, in MHz, that the protocol uses. Mobile phones supporting GSM 900 and GSM 1800 will ensure coverage in Europe and many other areas outside of the US, while GSM 850 and GSM 1900 are used in the US ( mostly GSM 1900 ).
Fortunately, smartphones support multiple bands to ensure as wide a coverage as possible. It’s common to have tri-band phones that support GSM 900, GSM 1800 and GSM 1900 to ensure maximum international coverage – although some still offer separate US models to reduce costs.
A GSM phone uses a Subscriber Identification Module (SIM) to gain access to the GSM network. A SIM contains all the pertinent information regarding a user’s account including the services allowed. It is used to identify the user to the GSM network for billing purposes. The user can switch their SIM from one GSM phone to another, provided that the phone is not locked either to a specific carrier or to the carrier that the SIM is associated with.