 stations to MSC should see very low delay almost all the time because the MSC is carrying real-time voice traffic and may be carrying real-time video as well. Because the backhaul network may be complicated not only by a multiple-hop backhaul configuration but also by redundancy in the network with some alternative packet routing, it is important to monitor backhaul links and to ensure high-quality packet performance. The system should be measuring packet delay on the backhaul links. As in any packet system, we can measure delay in two ways. The global delay can be determined by knowing when a packet is sent and when it is received. When the time stamps are far apart, the packet has been delayed. The other method is to measure the sizes of backhaul packet queues at the MSC and the base stations. In a multiple-hop link, the delay is the total delay time of all the individual hops. Different packet protocols have different measuring tools for delay and latency. Time stamps on data packets can be monitored to determine delay on any hop or path of mul- tiple hops. Also, packets can be sent and returned for a loopback test, which not only ensures that the link is running but also performs timing benchmarks. As quality-of- service (QoS) protocols are improved and deployed, monitoring methods and intelligent network response will continue to improve. Backhaul delay should be monitored routinely. Alert levels should be set so that we are automatically notified of any delay that might be noticeable to users or even a bit tighter than that at, say, 80 percent of the limit of acceptable performance. If alerts happen very seldom, then we may decide to live with occasional bursts of slow back- haul performance. If backhaul delay happens too often, then it will degrade subscriber service with noticeable dropouts in voice calls. 39.6 MSC Performance The MSC has several components that can become bottlenecks in a wireless telephone system. Each of these components should be watched so that congestion can be dealt with before it