ss a problem in identified and verified. For example, if one microwave link near the BSC in a chain is 'down' for few minutes, the network traffic and hence revenue generated from all the sites getting connected to that BSC would be lost. For this very reason, the transmission networks are not touched during the network optimisation. The process of transmission network optimisation is shown in Figure 3.25. When it has been identified that the transmission network needs to be optimised, the target areas for optimisation are defined. The process starts with the making of plans based on the data available and the targets to be achieved. These plans are then assessed and optimised, achieve a balance between costs, quality and the time frame for the process. The process of optimisation generates some plans, and these plans are then analysed. Again, based on the requirements and the costs, a master plan is prepared. This master plan is then implemented. Unlike in the radio network, where optimisation is an ongoing process, there is a gap period before the next optimisation cycle can begin in the transmission network. Gap Period Implementation of Master Plan Modifications Target definition Master Plan for the optimisation process Assesment Optimisation of the plans Process start-up Figure 3.25 Cellular transmission network optimisation cycle 3.5.2 Transmission Network Optimisation Process Process Definition There are two major reasons for transmission network optimisation: either capacity is less than desired, or the quality is not up to standard (see Figure 3.26). Once the main problem has been identified, the key performance indicators (KPIs) should be decided upon. The main KPIs in a transmission network are related to quality of the microwave links such as ESR and SESR. Apart from this, some parameters like slip frequency can be observed during a synchronisation study. Capacity Analysis During the initial network rollout, the benchmarks are usually on how many sites are on air. For going on air, the base stations ne