ed on the SIP. SIP messages are carried on top of the UDP/IP. If domain names are used the MSS/GCS may use a DNS to change domain names to IP addresses that may be used to route call control related signalling to the target MSS/GCS. The use of IP routing for signalling messages and of DNS to get those IP addresses eases tasks of configuration of signalling networks and is not limited by the number of MSS/GCS in the network. The need for a signalling transfer point is no longer necessary when using SIP. It has to be noted, however, that the use of the SIP in the release 4 circuit core is a vendor proprietary solution, and is not included in the 3GPP standards. 4.4.2 CS Network Dimensioning Dimensioning Inputs The actual process of network planning has already been discussed. The CS core network planning for 3G release 4 networks would follow the same planning process. It is important to remember that network Core Network Planning and Optimisation Migration/ Growth Target Network Phase 3 Phase 2 Phase 1 Pre-planning Optimisation Master Plan 1 Master Plan 2 Master Plan 3 Datafill Datafill Datafill Detailed Design Figure 4.11 Phased planning of the network (HLD, highlevel design) assessment is still a fundamental part of the process. If not explicitly carried out as a separate module, information gathered during network assessment is an important input for network dimensioning module. Prior to dimensioning the network, the following information should be agreed with the operator before performing network dimensioning: existing sites, floor space available, and transmission equipment installed and available capacity, ex- listing equipment technology, quantity and location; planned services to be provided by the release 4 network; subscriber forecasts, traffic profile, forecasts or measurements; country specific regulations, customer specific requirements; network element capacity and functionality roadmaps. Network Dimensioning The purpose of network dimensioning is to find the most cost-effective and technically opti