ion of our highways at rush hour. Frequent radio reports of accidents and delays allow drivers to select alternate routes during rush hour, optimizing their travel time to their destinations. This system has been enhanced in the last few years as drivers with cell phones have been calling to inform radio stations of accidents and delays. The sooner intelligence is passed to the agents capable of selecting routes, the more flexibly the network can respond, reducing traffic jams. Similar technology is being developed for networks. Several different designs are be- ing tested. There are two basic approaches. One involves using some type of central control for the entire network, and the other involves building intelligent routing ca- pability into each network device. In both approaches, it is crucial to have a method of signaling that informs devices of network conditions. The methods that use intelligent routers and switches rely on providing each device with information about network timing and delays. The devices use this information to make decisions regarding where to send voice packets and where to send data packets. Some systems report status using signals among switches and routers, and others use timing codes included in the data packet headers. Timing methods are, at present, used on Asynchronous Transfer Mode (ATM) networks but not on IP networks. In ATM, ATM adaptive layer 1 (AAL1) cells can provide information to the network, but the func- tionality of that information is somewhat limited. The signaling approach uses network overhead, but it has an advantage over the timing-code approach. When the timing codes are read by a router or switch, the node can calculate what is happening on the part of the network from which the packet came. However, the information only de- scribes what happened to the packet as it was heading toward the switch. It does not provide any information about the status of the path away from the switch. This limi- tation of the timing-code approach means that the device, in decid