n though it is working well at present. The new capac- ity starts with new sectors and perhaps new cells and works its way back to the land- line world. This means more backhaul, more MSC equipment, more signaling re- sources, and more transport to the landline networks. This capacity expansion may require more MSCs and auxiliary equipment, as described in Secs. 34.6 and 43.6. The system also may need to change, to serve a changing subscriber community, us- ing a different mix of services. We hope that this is associated with a growing sub- scriber community SO that we can add new equipment rather than changing old equip- ment. The change can be a shift from voice to data service, but it also can be growing demand for cellular snapshots in the form of MMS or even real-time video calls. What- ever shift there may be in subscriber demand, we have to make sure that the wireless telephone system is able to serve the changing demands well enough to ensure a rev- enue stream. Classically, the distinction between repair and improvement is this: Repair returns a system to its prior operating status or brings it to the QoS level committed to in a service-level agreement (SLA) or similar specification. Improvement is change that re- sults in performance better than what was previously achieved or exceeding the previ- ously defined standard or specification. Sometimes the line between repair and improvement can get blurry. We call a ven- dor to fix a software problem in the packet data switching area, and we are told that the repair requires us to buy a new software release that also will increase packet data switching capacity. Are we fixing a broken piece of equipment, or are we buying an en- hancement to serve subscribers with more packet data? We are constantly updating parameters, upgrading software, modifying configura- tions, and adding equipment. Each of these changes should be justified by a need in the wireless telephone system, fixing performance or capacity, adding capacity for growth, or following trends in the