rging gateways (CG), firewalls (FW), and the G-interfaces as shown in Figure 9.4. (Note: Fig. 9.4 forms part of Fig. 5.1). Network Dimensioning We have already seen most of these elements in Chapter 4, but there are some differences in 2.5G and 3G packet core networks. One is obviously the data rate, which is higher in 3G. The evolution of networks also brings new challenges with the increase of the number of PDP CORE NETWORK PLANNING PROCESS Corporate Intranet Corporate Intranet Router Network Internet Figure 9.4 Elements and interfaces to focus on in 3G packet core network planning contexts. In early releases of GPRS, there is only one PDP context per access point for one subscriber. However, with the new releases and quality-of-service (QoS) differentiation, the network is able to handle several PDP contexts per access point for one subscriber. This has an impact on the GSN dimensioning as discussed in Chapter 5 (in transmission network dimensioning). As data increases in 3G in terms of type, rates, etc., the SGSN and GGSN dimensioning becomes more complex them in previous chapters. Predictions for the number of subscribers, voice and data, are very important, as they give an indication on the PDP context and data traffic that will be needed in the dimensioning process. Although overheads were taken into account in 2G networks, in 3G networks they play a more crucial role. In fact, the impact of overheads in quite substantial in all three parts of planning, for radio, transmission and core. In the packet core network, overheads affect the capacity and subsequently the quality of the network. Overheads in the packet core network can be calculated on the basis of the protocol stack shown in Figure 9.5. The overheads due to each layer needs to added to during the dimensioning phase. Layer 1 (L1) is the physical interface while layer 2 (L2) is the ATM (or Ethernet) layer. The percentages of overheads due to each of these layers depend upon the traffic. Dimensioning of border gateways (BG) and firewalls (FW) is ano