ace planning solutions) are a part of the PC core network detailed plans. Traffic calculations are required so that traffic can be distributed equally between GGSNs. One way to send traffic is in a round-robin fashion whereby the traffic is sent to the next available GGSN. Another way could be a DNS deciding to which GGSN the traffic is routed through to the SGSN. Also, the amount of traffic is another factor to consider when deciding the routing for the traffic between the GGNs as it can be on an equal- or unequal-sharing basis. G interface planning involves one more network element, the charging gateway. Infor- mation exchange or message transfer between the GSN and charging gateways is done using GTP-based protocols. Inter-connections between these network elements are planned based on the capabilities of the network elements and network configuration. One of the possible ways to inter-connect these elements is to use virtual LANs along with the planning of IP addressing, redundancy of paths and associated signalling etc. 9.4 CORE NETWORK OPTIMISATION The optimisation process is quite similar to that seen in GSM/GPRS/EDGE core networks. Again, quality of services is an important backdrop against which the optimisation needs to be done (see Figure 9.10). Definition of key performance indicators (KPIs), analysis and preparation of the final optimisation plan are almost the same as what has already been discussed in Chapter 4 (for the CS core) and Chapter 5 (for the PS core). The final optimisation plan will consist of suggestions for changes to the existing network elements (e.g. increased capacity), new network elements and their locations, definition of allocation of transit elements and layers, new simplified number plans, etc. Also covered is optimisation END-TO-END QUALITY OF SERVICE Data Collection Final CN Definition Analysis CS & PS Optimisation Plan CS & PS Figure 9.10 3G core network optimisation process of the interfaces within the network, such as I-cs, Iu-ps and Gn, and interfaces to external networ