uirements imposed by the operator. Should there be a resiliency requirement to introduce some redundant capacity margin, then it should be taken into account when dimensioning the MGW elements. End-to-End Traffic Matrices The initial number and location of the MGW and MSS/GCS is determined by the number of users served by each MGW element. The number and location of MGW elements together with other network information gathered during network assessment (e.g. service supported, number of users, traffic profiles per user) are used to calculate end-to-end traffic matrices. The end-to-end traffic matrices show the traffic intensity between any two MGWs in Erlangs. As the user plane traffic is routed by MGW elements, end-to-end traffic matrices are therefore a valid support in deciding the interconnection architecture and represent the first step in network element dimensioning. The end-to-end traffic matrix may be calculated using specialised tools, e.g. the interswitch module of the NetAct Transmission planner. It is also possible to use measured traffic values if available. The calculations are based on CS network dimensioning principles. The traffic matrix should be studied carefully and compared with the available data in order to start the dimensioning process using the conect assumptions. Core Network Planning and Optimisation Figure 4.14 MGW transit layer concept MGW Interconnection Architecture and Transit Layer Concept All the MGWs controlled by the same MSS/GCS are part of the same MSS area. In order to minimise the number of elements on the user plane path for a call generated and terminated in the same MSS area, the MGW in one MSS area should have direct links. The architecture of the MGW under the same MSS area should therefore present a full meshed structure. In large networks with several MSS areas, there is a possibility of having a fully meshed architecture between all the MGWs or of selecting transit MGWs for inter-MSS area traffic. Figure 4.14 presents an example of MGW transit layer topology. The 