GSM (Global System for Mobile Communications) is a digital cellular communication standard developed for transmitting voice calls, SMS messages, and data over second-generation (2G) mobile networks. GSM became widely adopted in many countries and was one of the technologies that laid the foundation for modern mobile networks.
Unlike first-generation analog systems, GSM uses digital transmission. The standard also uses SIM cards to identify subscribers on a mobile network.
How GSM Works
The area served by a mobile network operator is divided into cells. Each cell is served by a base station that provides radio communication with nearby mobile devices.
When a user makes a call or sends an SMS message, the phone establishes a radio connection with a base station. The information is then transmitted through the operator’s infrastructure, which handles connection routing, subscriber identification, and communication with other networks.
As the user moves, the network can transfer an active connection between neighboring base stations. This process is known as a handover and allows a call to continue while the user is moving without having to establish a new connection manually.
To share radio resources among multiple subscribers, classic GSM uses a combination of FDMA and TDMA: the available frequency spectrum is divided into radio channels, and each channel is divided into time slots.
Components of a GSM Network
A classic GSM architecture includes several main components:
- Mobile Station (MS) — a mobile device together with its SIM card.
- Base Transceiver Station (BTS) — a base station that provides direct radio communication with mobile devices.
- Base Station Controller (BSC) — a controller that manages a group of base stations.
- Mobile Switching Centre (MSC) — a switching center responsible for establishing and routing connections.
- HLR and VLR — databases containing information about subscribers and their current location within the network.
This architecture allows an operator to serve a large number of subscribers and maintain their connections as they move between different coverage areas.
Data Transmission in GSM
GSM was originally developed primarily for voice communication, so data transmission capabilities in classic GSM networks were limited. Packet-switched data technologies were later added to the standard.
GPRS (General Packet Radio Service) is often referred to as a 2.5G technology. It enabled GSM networks to provide persistent packet-based internet connectivity without establishing a separate connection for each data transmission.
The next development was EDGE (Enhanced Data rates for GSM Evolution), which provided higher data transmission speeds through more efficient modulation methods.
With the introduction of 3G, 4G, and 5G, the role of GSM in mobile internet access has decreased significantly.
Where GSM Is Used
Despite the development of newer generations of mobile communications, GSM remains in use in a number of countries. In addition to conventional mobile phones, various telemetry and machine-to-machine communication devices can connect to 2G networks, including meters, security systems, payment terminals, GPS trackers, and industrial equipment.
At the same time, operators in many countries are gradually shutting down 2G networks and reallocating their frequencies to newer mobile standards. Therefore, when choosing equipment with a GSM module, it is important to consider the specific operator’s plans for continued 2G support.