network, a routing table is used. This contains all the information needed to route data to the required destination within the network, or to a local gateway if the destination address belongs to an external network. GPRS: NETWORK PLANNING AND OPTIMISATION 5.6 NETWORK OPTIMISATION Steps in the optimisation of a GPRS network are the same as for a GSM network (explained in Chapter 2) and involve definition of key performance indicators (KPIs), network per- formance monitoring and parameter tuning. However, GPRS network optimisation is more complicated because it uses the resources, such as frequencies, of the existing GSM network. The optimisation process will focus on improvement in the following areas: Accessibility to the network: The mobile subscriber should be able to get the desired service when it is requested. Quality: A requested service should come along with the desired quality. Utilization of the resources: The air, Abis and Gb interfaces are optimised. CS and PS: There needs to be improvement in both the CS and PS quality levels along with the improvement in coverage and capacity. Security: Security aspects of the network need to be reviewed. The whole process can be divided into radio network, transmission network and core network optimisations. Only the radio and packet core network optimisation processes are covered here; see Chapters 3 and 4 for processes relating to the transmission and CS-core networks. 5.6.1 Radio Network Optimisation As the GPRS (data) traffic runs on the GSM radio network, there are some complications that should be taken into account. Optimisation of the GPRS (data) network involves op- timisation of the GSM radio (voice) network. This means there is a conflict between the priority of voice and data calls. Usually, voice calls take priority in such networks, SO that the capacity/coverage and quality requirements of the mobile (data calls) subscribers are even more difficult to fulfil, leading to a continuous process of GPRS network optimisation. Coverage in GSM and GPRS is d