n is done to transmit data between two terminals via a channel. Each layer in the OSI model is responsible for some tasks (multiplexing/de-multiplexing, segmenting/de- segmenting, compressing/decompressing, etc.). Layer 3 is the most relevant for physical connection reliability. The radio interface carries bursts of the size of 114 bits; formatting is therefore very important. Layer 3 contains three sublayers. Radio Resource (RR) Management RR management is responsible for setup, maintenance and termination of a dedicated radio channel connection. It englobes procedures for managing shared transmission resources. An RR connection may be released and re-established on another physical layer several times during a single p-2-p connection between two terminals. Radio Network Planning and Optimisation Mobility Management (MM) This entity controls mobility of an MS and authorisation to access the network. MM manages the identification, authentication and allocation of new TMSI. It also mainly handles the procedures of IMSI attach, IMSI detach and location update. Call Management (CM) CM is useful for setup, maintenance and termination of circuit switched calls. It is in its turn divided into three entities (call control, short message service and supplementary services). Call control (CC) provides the transport layer with a p-2-p connection. CC is responsible for call establishment, call re- establishment and call clearing. For more details on the network layer, the reader can refer to the GSM recommendations For optimisation purposes, this layer is the most commonly analysed as it detects network problems. Protocol Trace Exploitation in Optimisation Based on what has previously been explained in this section, here the practical applications are presented, and it is shown how daily optimisation uses signalling charts to improve network quality. The idea is first to present and explain the signalling charts of the main quality events of the GSM system (e.g. MTC, MOC, LU, etc.). An indications is then given of how to mo