affic. Other MSC-to-MSC communication is separate from handoff communication. Consider the handoff process at its most basic level: A call changes from one cell sec- tor to another. If the two sectors are in the same cell, then the MSC may not even need to know about it. If the two cells are served by the same MSC, then the one serving MSC handles the circuit switching, and the handoff has no need for MSC-to-MSC com- munication. When the call crosses an MSC boundary, however, one MSC needs to com- municate with another. For this section we need only consider the capacity require- ment of handoffs that cross MSC boundaries. Let us consider a handoff in more detail. Several cells and the user terminal make measurements and determine whether there should be a handoff and where it should go, and not all of these cells are served by the same MSC. ANSI-41 specifies how MSCs communicate with each other to make measurements for inter-MSC handoffs, how they complete the handoffs, and how they maintain efficient paths through multiple inter- MSC handoffs. Once two MSCs use the signaling network to decide to do an inter-MSC handoff, they use dedicated facilities between them to carry the subscriber's voice and data traffic. While these links may follow the same physical paths as the PSTN links used for roam- ing or call forwarding, they are not the same logical paths because they perform a dif- ferent function. Logical and physical models are discussed in Sec. 14.4. Multiple-handoff path minimization is important in today's wireless world. If we ture a user moving from system to system to system in a linear fashion, say, Boston to Hartford to New York, then the notion of multiple inter-MSC handoffs may seem like a rare event. 6 Increasing demand for wireless service has increased traffic density and Back in the early days of cellular, when we were working on abutting systems, we wanted to claim that one could start a call in Boston and drive all the way to Denver without losing the call. None of us could think of any reason