GSM (Global System for Mobile Communications)

Global System for Mobile Communications or GSM.
a cellular digital telecommunications standard.
first implemented in Finland in December, 1991.
widely used in more than 200 nations and territories.
shares frequency spectrum using time division multiple access (TDMA).
supports digital services, SMS, and circuit-switched phone calls.
uses SIM (Subscriber Identity Module) cards to identify users.
incorporates security components like authentication and encryption.
adapted to enable General Packet Radio Service (GPRS) and Enhanced GPRS (EDGE)'s higher data transfer rates.
lays the groundwork for 3G (UMTS) and 4G (LTE) network technology.

General figure of GSM working

GSM operates on the principle of dividing a geographic area into smaller cells to provide wireless coverage.
A base station that provides service to each cell communicates with mobile devices in its coverage area.
The mobile device contacts the closest base station whenever a user places a call.
Call routing and network management are handled by the Mobile Switching Center (MSC), which is connected to by the base station.
The MSC chooses the recipient's mobile device or another network as the call's destination and establishes a connection with it.
Voice signals are encoded, compressed, and transferred as digital data via the GSM network while a call is in progress.
GSM uses Time Division Multiple Access (TDMA) to divide the frequency spectrum into time slots, allowing multiple users to share the same frequency.
Each call is assigned a specific time slot within a frequency channel to prevent interference.
GSM uses Frequency Division Multiple Access (FDMA) to assign different frequency channels to different cells.
The SIM card in the mobile device contains user-specific information and enables network authentication.

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