elements in an IN network is the IP (an intelligent peripheral). This is basically a stand-alone processor that provides the additional services for which IN is implemented in a network. IP functions include IVR, DTMF (dual-tone multi-frequency) translation, speech recognition, providing access to the signalling networks, etc. CORE NETWORK PLANNING AND OPTIMISATION Taking into account all the above factors, the number of signalling links can be calculated. Usually, network planning tools are used for this (see Appendix A). The output of signalling network dimensioning is the required number of signalling links. Once this is done, the number of ET ports can be calculated. 4.5 FAILURE ANALYSIS AND PROTECTION As noted earlier in this chapter, the number of switches is fewer than the number of base stations or base station controllers, and in some cases there is only one switch in the network. A minor failure in the core network may lead to a large part of the radio network becoming non-functional, leading to a huge revenue loss. Protection of the network therefore becomes an inseparable part of core network planning. For designing (or assigning) protection, it is important to know the main failures that may take place in a network. These are: site failure equipment/node failure. A site rarely fails. If it does, this is usually due to conditions that are beyond human control - flooding, earthquake, fire, etc. Although natural calamities cannot be prevented or their effects predicted, some steps should be taken to minimize the likely damage they cause. This may include choosing a site at a higher altitude in regions where floods are common, avoiding buildings or locations that do not have proper fire detection and preven- tion equipments, and adequate cooling arrangements to prevent over-heating of network elements. Apart from site failures, small failures arising from power or transmission problems may lead to temporary failure of the equipment or node. One MSC and one HLR handle respectively about 0.5 million and on