sis and assist the field engineer in interpreting messages. They are tools that may be connected to the BTS, BSC or MSC over a period of time to generate trace files. In the case of problems, manual analysis starts. Generally signalling measurements are performed on the BSS part where more network elements and parameters exist; hence, hardware and tuning problems are more probable in the NSS. When used in NSS signalling analysis, the protocol analyser mainly highlights problems in interworking of protocol implementation. Automatic analysis of protocol traces is possible through specific software packages developed by the manufacturer. It offers postprocessing in the shape of graphs or tables that present one level up in interpreting and summing of events per cell or area. In the manual analysis scenario, the task is more time consuming and requires from the field engineer a deep knowledge of protocols and signalling charts. The Radio Network Optimisation Coverage Capacity Quality Figure 2.64 Network performance constraint evolution path main task consists of making use of filters and search functionalities to detect errors and then interpret and analyse them. There is a close interaction between signalling charts and counters. Step by step, while messages flow in both uplink and downlink ways, timers and counters are incremented and decremented. Therefore, the philosophy of upstep and downstep is dependent on the message. Timers are indicators generally expressed in seconds; they start counting down when the network sends a request and is waiting for the other side to answer. When they expire, a failure counter is incremented and the system itself takes the decision to either terminate the transaction, for example, or re-initiate a certain phase. On the other hand, most of the request, acknowledgement, nonacknowledgement, failure, rejected, seizure, assignment and complete messages result in an increase in several counters. Counters seen before are relevant items to estimate the quality of service before and afte