f the user terminals. Different subscriber equipment may have different levels of radio waveform distortion, adding different amounts of noise to the CDMA channel. This variation is not only call by call but also moment by moment. A subscriber walks into a building, and the CDMA channel goes from barely good enough to not good enough for that call or perhaps for other calls on the same carrier. The wireless service provider has to make some decisions about service quality in an- ticipation of changing radio channel conditions. Consider this example for planning ca- pacity for a particular sector. If the average call duration is 2 minutes (120 seconds) and the expected capacity is 24 calls, then the expected time until somebody hangs up normally is 5 seconds. In this case, if worse than usual conditions do not allow high- quality calls when the twenty-fifth call comes in, then the subscribers experience about 5 seconds of excessive interference before someone hangs up. This may be acceptable if it happens occasionally, but if it happens too often, subscribers will be dissatisfied with the service. If this network continues to allow a twenty-fifth caller onto the system, then service may be unsatisfactory. The network can anticipate the increased error rate and block calls, maintaining a maximum of 24 calls in the sector under these condi- tions. The tradeoff between capacity and quality manifests itself in the decision whether to hold the line at 24 calls of good quality or to allow 25 calls and to tolerate the occasional 5 seconds of substandard voice quality. 12.5.8 Varying overflow characteristics Overflow is the capacity of a network to provide alternate routing if demand exceeds the capacity of the normal or primary route of a call. On the traditional PSTN, if connection from switch A to switch B is full, it might be possible to carry the overflow from switch A to switch C and then from switch C to switch B. However, in the tradi- tional PSTN, there is no alternate route to replace the local loop. Overflow in