• The BTS used in a GSM network comprises the radiotransmitter receivers. It is the defining element for each cell .
• The BTS communicates with the mobiles and the interface between the two is known as the Um interface with its associated protocols.
• The BSC forms the next stage back into the GSM network. It controls a group of BTSs, and is often co-located with one of the BTSs in its group.
• It manages the radio resources and controls items such as handover within the group of BTSs, allocates channels.
• It communicates with the BTSs over what is termed the Abis interface.
• The main element within the core network area of the overall GSM network architecture is the Mobile switching Services Centre (MSC).
• It provides registration, authentication, call location, inter-MSC handovers and call routing to a mobile subscriber.