le traffic. If we assume decentralized Media Gateway (MGW) configurations, one MGW in each switch centre (i.e. A, B, and C) will handle capacities > 8000 Erlang CS traffic and >500 kpps packet switched traffic in each city. configurations as needed. Table 7.25 illustrates the value for the assumptions. Initially, to consolidate the functionality and operation of MGW (new on CN) we can centralize it in one city where there is high-density traffic, e.g. city A. Then we can ex- pand it to other cities as need arises. Or we can start with one MGW in each city to fa- cilitate network lay-out. In this study we choose the latter for the first years starting 2002. The UMTS Network and Radio Access Technology We also estimate the total simultaneous data sessions (SDS) and distribute them throughout the three cities. The SDS allows us to estimate the traffic interaction, e.g. in the PS network, which occurs based on the number of subscribers attached. The latter depends on the GGSN and SGSN capacity for handling PDP contexts and throughput. For example, a GGSN capable of handling 500K PDP context and a throughput of 500 kpps with a SGSN also handling 500K PDP contexts and supporting 400K simultaneous attached users can serve as reference here. We can also assume that the proportion of traffic passing through the cities are: city A 45%, city B 30%, and city C 25%. Table 7.25 MGW PS and CS, GGSN and SGSN Configurations 2002 and 2005 Location GGSN configura- SGSN configura- Simultaneous MGW configura- tion (min. 300K tion (min. 300K data sessions (e.g. tion 8400(E) 540 subscribers) subscribers) 5K SDS package) (kpps) City A City B City C Total The SGSN and GGSN servers control the PS traffic. Thus, the number of GSN servers depends on the number of simultaneous packet data sessions. Because the data packets are switched in the media gateways, the data volumes in the network do not influence the dimensioning of the GSN servers. Likewise, the MSC server controls the circuit switched calls, and only the total circuit switched tr