e depends on the total duration of calls. If there is a trend toward shorter voice calls, then the circuit- switching components of the MSC will have to increase. If the trend is toward longer voice calls, then we have to add more speech-coding equipment. The packet-switching component of the MSC serves the backhaul packet pipes, data services, and most of the other services. If there is steady growth in 3G services, then we expect an increasing share of the MSC workload to be packet switching. This means that the packet-switching equipment has to keep up with an increasing share of in- creasing traffic. In expanding the MSC, it is important to think about not only adding equipment but also making equipment better. Technology gains can make upgrades attractive because they increase capacity at lower cost. If the new version of a piece of equipment saves money, then this is good. If it means that the total capacity of an MSC is greater so that we can postpone purchasing a whole new switch, then this is even better. Upgrading equipment offers more than cost and capacity advantages. Often new equipment offers capabilities and features not available earlier. For example, if a new speech coder is developed that provides high-quality speech in 4800 bits per second, then we can install these speech coders in the MSC, sell user terminals with them, and realize an air-interface capacity increase for those subscribers with the new cell phones. As another example, a more efficient backhaul compression scheme for the packet link could be installed at the MSC and at the busiest base stations. Many of these upgrades are not capacity-driven but vendor-driven. Our equipment supplier makes us aware that there is a better piece of equipment that will save us money or will serve more subscribers or, perhaps, will be more reliable and easier to service. There is typically a window of upgrade opportunity between the first introduc- tion of new equipment and the end of support for the old equipment. 1 Early in the up- 1We all have sor