ther part of core network, planning. Any given 3G network will have diverse types of data traffic, and will interact with different types in other networks. Thus, firewalls become more important in 3G networks. SNDCP UDP/TCP UDP/TCP BSSGP N/W Services Figure 9.5 Protocol stack in a PS network 3G CORE NETWORK PLANNING AND OPTIMISATION BG dimensioning is dependent on the number of 'own' subscribers in external networks and external subscribers in the 'own' network. Firewall dimensioning may not be a part of the initial network plan, but it will be required in the later stages to protect the network from 'intruders'. Core network planning engineers should remember that other factors - such as redun- dancy of equipment - is highly recommended in the core network, but cost implications should be considered as well. 9.3 DETAILED NETWORK PLANNING 9.3.1 Circuit Switch (CS) Core Network The detailed master plan for the CS core will include plans related to routing, signalling and parameter settings. All these are based on the core network plan that is an output of network dimensioning (though it may change in the detailed planning phase). Elements The network plan consists of the CS core network elements such as MSC, MGW and the inter-connections of these elements amongst themselves and with other elements in the cellular network. A CS voice network plan, as shown in Figure 9.6, contains the connection between the MGW and MSC. This plan also indicates the capacity required for the link (four E1s in the example). Apart from this, the routing plan for both voice and signalling is required. This plan contains primary routes and secondary routes for carrying the voice and signalling traffic. A load sharing factor is also decided. The locations of the MGWs/MSCs, inter-connections between them, connection between the 'own' network and external networks, etc., should be decided. In the core network, elements can be inter-connected physically or logically or in both ways. In the present scenario of 3G core networks, physical conn