GSM

GSM, or Global System for Mobile Communications, is a standard for second-generation (2G) mobile networks developed in Europe and adopted worldwide. It originated from the Groupe Spécial Mobile initiative and was standardized by the European Telecommunications Standards Institute (ETSI) in the 1990s as a successor to analog mobile systems. GSM networks became the dominant 2G technology in many regions and laid the groundwork for ongoing global roaming and interoperability among mobile operators.

Technically, GSM uses a combination of frequency-division multiple access (FDMA) and time-division multiple access (TDMA). Each carrier is divided into 200 kHz channels, and each channel is further subdivided into eight time slots for simultaneous users. The standard employs digital speech encoding and the GMSK modulation scheme, with a modular network architecture that includes mobile equipment (MS), base transceiver stations (BTS), base station controllers (BSC), and mobile switching centers (MSC). Subscriber data and mobility management are handled by databases such as the Home Location Register (HLR), Visitor Location Register (VLR), Authentication Center (AUC), and Equipment Identity Register (EIR). A Subscriber Identity Module (SIM) card stores the subscriber’s identity credentials and security keys, enabling roaming across networks that support GSM.

In addition to voice, GSM introduced data services. Circuit-switched data offered modest speeds, while later enhancements provided packet data access through GPRS (2.5G) and later EDGE (2.75G), delivering tens to hundreds of kilobits per second and enabling more practical mobile internet use. Commercial deployment occurred on multiple bands, notably 900/1800 MHz in many regions and 850/1900 MHz in the Americas, with roaming enabled across networks that share the standard. Today, GSM networks coexist with newer generations, serving as a foundation for voice and legacy data services while 3G and 4G technologies handle higher-speed mobility.