The GSM protocol stack

The protocol stack for GSM follows the basic concepts of the ISO OSI 7 layer stack in so much as it is a layered architecture. The relationship between the three layers as defined in the OSI model and those in GSM are described along with a breakdown of the functions performed by each layer. GSM Layer 1 is normally understood to mean the control software which controls the radio and baseband hardware-the physical layer. Layer 1 multiplexes the physical access to the radio channel and provides a number of logical channels which can be used for signalling. Layer 2 is responsible for establishing a data link on these logical channels to allow reliable transmission of Layer 3 signalling messages. Layer 3 is subdivided into a number of separate tasks including the radio resources manager, the mobility manager, and the connection manager