ty Planning In planning, we must ensure that our network has the capacity to handle the signal load at peak capacity. This includes the signaling load required by the ANSI-41 stan- dard (including short message service support), as defined in Chap. 15 and discussed in Chap. 25. It also includes signaling required between base stations served by a sin- gle mobile switching center (MSC), which are not included in the ANSI-41 standard, and any other signaling features available on proprietary equipment that exceed the ANSI-41 standard, such as support for inter-MSC soft handoff. Although we are able to define all the types of signaling messages, and we have pro- posed methods for estimating them, it is difficult to develop precise statistical measures of signaling demand, such as the number of handoff measurements per minute per call for a particular geographic area. Due to the lack of precise, measured input, it is proba- bly better to err on the side of caution and allow some extra capacity for signaling. This is not excessively expensive because each signal is small, so adding a significant margin for error does not require a major investment in equipment or transport. 36.1 Handoffs Handoff activity generates communication messages between base stations. When the base stations share a common MSC, their handoff messages go through the MSC. When the base stations involved in a handoff are served by different MSCs, the MSCs use ANSI-41 messages to determine the need for a handoff, to establish the handoff, to make the required connections, and to end the handoff. The ANSI-41 specifications to date do not require soft-handoff capability between base stations on different MSCs, but several vendors support inter-MSC soft handoffs. The ANSI-41 signaling network is involved with any inter-MSC handoff, whether not it is on the same wireless telephone system. In the jargon of ANSI-41, any change of MSC is a change of system. In estimating the ANSI-41 signaling load for signaling capacity planning, we care about inter-MSC h