rhaps some antennas need to be downtilted. If the cells are handing off properly, then there may be more traffic moving across the MSC-region border than we had anticipated in the system design. In such a case, it is time to get more facilities there. We also can have dedicated links between MSCs to save PSTN costs for some roamer terminations and for mobile-to-mobile calls. These facilities are used to reduce costs rather than to provide a vital function, so we should be measuring their occupancy. If they are not carrying enough traffic to pay their own way, then it is time to reduce the size of these dedicated inter-MSC packet pipes. The traffic actually on the facility de- termines how much money it is saving us in PSTN charges. 39.8.4 Backhaul links Backhaul link engineering should be easier than most other transport because we know the capacity of the air interface. Thus we should have few surprises from the base station to the MSC. With few exceptions, packets over the air become packets to the MSC. Different vendors handle the channel data differently on their packet links. Most use compression schemes, so the backhaul links are not perfect data mirrors of the CDMA air interface. The CDMA carrier does vary in capacity due to changes in the environment. Calls from areas of low radio signal path gain consume more of the CDMA radio resource, but this is not going to overflow the backhaul link. A CDMA carrier will have more capac- ity if neighboring cells have less traffic than usual due to some cause or just due to sta- tistical randomness. When this happens, the backhaul link might be the bottleneck. We should measure backhaul packet link delay. If this delay becomes significant, then we should act. Most likely, the action we will have to take to fix a backhaul delay problem is to call the maintenance technician and have him or her repair a failed DS-1 or E-1 link. 39.9 Conclusion Monitoring the status of our entire cellular network, especially these crucial measures of performance, allows us to identify pot