The Global System for Mobile Communications (GSM) is the foundational standard for second-generation (2G) digital cellular networks. It was developed to provide a unified digital mobile system that facilitates seamless international roaming and secure voice and data services.
GSM uses a layered protocol structure for communication between the mobile station and the network: GSM – Architecture, Protocols and Services
Handles the radio link with mobile devices. It includes the Base Transceiver Station (BTS) , which contains the radio transmitters and receivers, and the Base Station Controller (BSC) , which manages radio resources and handovers for multiple BTSs. The Global System for Mobile Communications (GSM) is
Manages call control (CC), Short Message Service (SMS), and supplementary services. Services and Security and the Base Station Controller (BSC)