 simple to estimate because they are directly related to voice-call activity. A call starts, a call stops, a call-waiting call comes in, a three-way call goes out, and a call ends. Each of these involves a fixed amount of switching activity. Circuit-switched data channels such as Integrated Services Digital Network (ISDN) follow the same rules. The connection is made, the connection is broken, and not much more happens to an ISDN call. Direct data packet service is no work at all for the circuit-switching component of the MSC. Packets come in and go out through packet handlers, and no circuit switching is required. The wireless environment adds one enormous monkey wrench to the circuit-switch- ing load-handoffs. If the typical call averages 1.5 handoffs, then this multiplies the switching load by approximately 2.5 compared with a network with no handoffs. 4 Soft handoff may keep other MSC components busy, but it is no worse than hard handoff for switching. The estimate of handoff activity per voice call can be an important calcula- tion for MSC capacity. It is not clear, however, that handoffs must involve circuit switching at all. Some ven- dors maintain a pure packet link between the base stations and the MSC. In this case, the packet handler routes the compressed-speech voice packets based on their address. Even a handoff to another MSC may use a virtual circuit over a packet link and there- fore may require no circuit switching. 24.4 Packet Switching Going down the list of MSC functions and resources, there seems to be a pattern. We seem to be putting more and more work into the packet handlers. Therefore, let us examine what these packet handlers might be doing and how their capacity is engineered. The packet component of the base-station-to-MSC link goes through the packet han- dler. If the speech is packetized, then the entire base-station-to-MSC link is a packet link and goes through the packet handler. The voice packets go to the speech coding Some telephone companies provide an always-on ISDN service th