en limited to signalling. Radio Resource and Mobility Management The management of radio resources, functions related to mobile location update, communi- cation management issues such as handover and roaming procedure handling, come under radio resource management (RRM). For these management functions to happen, informa- tion flow (traffic and signalling) takes place via three protocols, known as link protocols (see Figure 2.14). LAPDm is present over the MS-BTS connection and LAPD over the BTS-BSC connection. MTP (message transfer protocol) is used for signalling transport over the SS7 network. LAPDm Figure 2.14 Link protocol in a GSM network RRM procedures basically relate to the processes taking place during transitions between different states of the mobile station, such as the idle state, the dedicated state, during mobility, during handover, when calls are being re-established, etc. In GSM, there are two states that are defined for a mobile: idle and dedicated. Thus, from an idle state, the mobile station enters a BTS access mode wherein 'access' is granted to the mobile based on whether or not the mobile station is allowed to 'use' the base station. Then the mobile station enters the dedicated mode and starts using the resources until it enters the release mode, i.e. the call ends. Once a mobile is logged into the network, the transition procedure request always comes from the mobile, and this is done through the random access channel (RACH). As the timing of requests coming from mobiles cannot be predetermined, this may cause problems such RADIO NETWORK OPTIMISATION as 'collision of call request'. Then factors such as congestion, the call-repetition process, traffic increase, etc., come into the picture. The radio planner should keep the throughput under control by means of parameters such as the number of times the request for a channel can be sent, and the timing of re-requests (which is usually kept 'random'). Paging is another function whereby, when a request from the mobile reaches the MSC, then the 