e million subscribers (these values depend on the equipment manufacturer and individual equipments capacities). Thus, if one MSC or one HLR fails completely, revenue is lost from 0.5 to 1 million subscribers. Using redundant MSC/HLRs is one way to reduce the lost traffic. The situation in networks having just one switch is quite severe in cases of failure. In networks having more than one switch, failure can be alleviated. One of the methods is to move the base stations from a failed MSC to another 'live' or redundant MSC. The second 'live' MSC should have enough capacity to handle the additional traffic. In traditional networks, the HLR data were transferred to the redundant HLR using DAT tapes. These days, real-time updating of subscriber data takes place between the 'live' and redundant HLR. Sometimes only part of some equipment may fail, but even slight damage/malfunctioning can lead to link or route failures. Typical examples of this are a damaged or disconnected PCM cable or ET port failure. There may be cases when route failure takes place, and existing routes experience higher loads leading to bigger delays. To cover these circum- stances, it is recommended to define more than one signalling link in each link set, and/or have a redundant signalling route. During dimensioning, each of the links should be over- dimensioned, SO that if there is a failure, the link should be able to carry extra traffic. Thus, there has to be a trade-off between the resources and failure protection in core networks. FAILURE ANALYSIS AND PROTECTION Output of Network Dimensioning As noted above, network planning tools are used for dimensioning and planning of a core network. Some results of the dimensioning exercise are explained below. Traffic calculations: Based on inputs such as the number of subscribers, calling interest, moving interest, forecast number of subscribers, etc., a traffic matrix is generated. Number of switches, their capacities and locations: The number of switches required is one of the main outputs of dimens