GSM

GSM

 GSM (Global System for Mobile Communications) is a standard for digital cellular networks that was developed by the European Telecommunications Standards Institute (ETSI). It was first deployed in 1991 and has since become the most widely used mobile phone standard in the world. 

GSM networks use a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA) to allow multiple users to share the same radio frequencies. This allows many users to communicate simultaneously over a single cell tower. GSM also introduced the use of SIM (Subscriber Identity Module) cards, which can be swapped between devices, allowing users to easily switch between different phones and service providers.

GSM has been replaced in many countries by newer cellular technologies such as 3G, 4G LTE, and 5G, but it still remains in use in many parts of the world.