Chapter Switching Capacity A mobile switching center (MSC) is a busy place, with processors, switches, speech han- dlers, and other equipment handling calls coming from dozens or hundreds of base sta- tions. 1 Each component must have the capacity to handle the workload for all its vari- ous tasks. In this chapter we look at each logical component and enumerate its tasks, laying out the picture of what needs to be done to estimate capacity for each component of the MSC. 24.1 Main Processor Capacity The MSC is a telephone switch that has extra responsibilities for the wireless part of the wireless telephone system. The main processor of the MSC is the computer proces- sor that figures out what the switch should be doing. The processor itself has to have enough computing power to do everything the MSC has to do. Therefore, let us go over the functions that the MSC main processor has to perform, and let us keep our eyes open for how much workload each presents. These functions include call processing, providing short message service (SMS), and managing handoffs. 24.1.1 Call processing The call-processing workload for the MSC processor is on a per-call basis. Once we es- timate the number of calls the MSC has to handle, we have a handle on the amount of computation the processor has to do. Each voice call originating from a cellular telephone served by the MSC uses pro- cessing resources. Each call involves analyzing dialed digits and deciding if the sub- scriber can make the call. For example, if a subscriber's telephone service has been can- celed due to reported theft or loss of the cellular telephone or due to nonpayment bills, the system will not allow most calls, but by law it must accept 911 emergency calls, even from these phones. The exchange of signaling messages with the home lo- cation register (HLR) needed for this type of validation uses processor resources. If the The term MSC is used ambiguously. Sometimes it refers to the central switch and its proces- sor, and other times it refers to the entire bui