GSMs

GSMs, or Global System for Mobile Communications, refers to a family of standards for digital cellular networks. Developed in the 1980s under the European Telecommunications Standards Institute (ETSI), the aim was to create a single, roaming-friendly system for mobile voice and data. By the mid-1990s, GSM had become the dominant 2G standard worldwide, paving the way for later technologies such as GPRS, EDGE, and UMTS.

The GSM network architecture combines a radio access network with a core network. The radio part includes the mobile station (the user device) and the base transceiver station (BTS), which is managed by a base station controller (BSC). The core network comprises the mobile switching center (MSC), the home location register (HLR), the visitor location register (VLR), and the authentication center (AuC). Subscriber identity is enabled by the SIM card, which supports roaming and authentication across networks.

GSM uses TDMA, a time-division multiple access method, with Gaussian minimum shift keying (GMSK) modulation. It operates in specific frequency bands, most commonly 900 and 1800 MHz in many regions (collectively known as primary GSM bands) and 850 and 1900 MHz in others (often referred to as digital cellular bands). Authentication and encryption protect communications and subscriber information.

Data services evolved from circuit-switched methods to packet-switched approaches. General Packet Radio Service (GPRS) introduced 2.5G data and was followed by EDGE (often called 2.75G) to increase data rates. The GSM framework was extended by the 3GPP family through UMTS and later evolved toward 4G and 5G networks, though GSM remains foundational for many networks and devices.

GSMs enabled widespread roaming, interoperability, and universal subscriber identity, making them a cornerstone of modern wireless communications.