 covered by a given MGW. The locations of the MGWs is another factor. An MGW can be distributed in the network (near the RNCs) or can be co-located near the core site. A distributed structure will result in transmission saving, but on the other hand it also leads to an increase in the number of MGWs, which in turn results in more inter-MGW connections. This increases the complexity of the network, making it difficult to maintain or expand. A concentrated structure decreases the equipment costs but increases the transmission costs. (Readers can draw the analogy from Chapter 3, where the concept of BSC location is discussed.) Also, in a concentrated structure, the complexity is less. In network rollout plans, both types of structure, distruted and concentrated, might be used simultaneously depending upon the requirements. Dimensioning of the number of MSCs (or MSC servers) depends directly on factors such as the subscriber base, their calling behaviour and the number of RNCs. The reason is that each MSC contains VLR in a limited capacity (i.e. can handle a specified number of subscribers and the number of attempts to log into the network). Every RNC can be connected to only one MSC. Once the subscriber base is known for the network, the traffic that is expected to flow in the CS network is calculated, using an approach similar to that outlined in Chapter 4. The traffic matrix will contain the traffic flowing in the network due to calls generated internally, and expected incoming calls generated in other networks. One small example is shown in Figure 9.3. Unlike a similar figure shown earlier (Figure 4.3), the traffic matrix contains MGW as the network element instead of MSC. External Network External Network Figure 9.3 Traffic generation (in Erlangs) 9.2.2 Packet Switch - Core Network Planning Network Analysis The packet core network is similar to that in GPRS network planning (refer to Chap- ter 5). The main elements include SGSN, GGSN, border gateway (BG), domain name servers (DNS), LIG, switches and routers, cha