'. Calling interest indicates the distance to which calls are made (i.e. long distance or short distance), as shown in Figure 4.3. This figure is useful for inter-switch modelling when distance Figure 4.3 Calling interest CORE NETWORK PLANNING AND OPTIMISATION calculating the number of subscriber-originated calls. Moving interest is another parameter that defines the subscriber behaviour of moving within the network. The external calls would then be diverted via the shorted path using the HLR-call enquiry feature. When the number of subscribers has been determined, the number of switches can be calculated. The subscriber number directly affects the visitor location register (VLR). Thus: Number of switches = number of subscribers/VLR (or HLR) capacity. When the number of switches has been determined, the next step to locate them. If there is only one switch, the decision is quite easy: it is generally located near the mobile headquarters or at a place having easy accessibility. In this case the expected traffic is also low, SO no routing plan is required as all the traffic goes to only one switch. However, the scenario changes quite a bit when there is more than one switch. The main idea is to keep the switch locations in areas of high subscriber density, thereby saving on transmission costs. Next, the traffic route needs to be defined. Routing may be done in two ways: partly mesh or completely mesh. Assume that there are four switches. The traffic can be routed as shown as in Figure 4.4(a), where all the MSCs are connected in cyclic fashion with some protection afforded by a diagonal connection. In Figure 4.4(b), all the MSCs are interconnected, SO traffic from each flows into the rest of the MSCs. Though the former technique is simple, it results in a higher amount of transit traffic. Obviously the traffic in the complete mesh is more protected. This is a simple case. If the number of switches increases then the mesh technique becomes more complicated and routing of all the traffic to all the switches becomes a 