Chapter 2 packet came in on. The switch then records in its routing tables an entry that dictates that all packets originating from the same source (the source being a virtual circuit address/physical port address combination that identifies the logical source of the packets) should be transmitted out the same switch port. This process is then followed by every switch in the path, from the source to the destination. Each switch makes table entries, similar to the blazes left by the Corps of Discovery.2 With this technique, the only packet that requires a complete address is the initial one that blazes the trail through the network wilderness. All subsequent packets carry nothing more than a short identifier-a virtual circuit address-that instructs each switch they pass through how to handle them. Thus, all the packets with the same origin will follow the same path through the network. Consequently, they will arrive in order and will all be delayed the same amount of time as they traverse the network. The service provided by connection-oriented networks is called virtual circuit service, because it simulates the service provided by a ded- icated network. The technique is called connection-oriented because the switches perceive that there is a relationship, or connection, between all of the packets that derive from the same source. As with most technologies, there is a downside to connection-oriented transmission: In the event of a network failure or heavy congestion some- where along the predetermined path, the circuit is interrupted and will require some form of intervention to correct the problem, because the network is not self-healing from a protocol point of view. There are cer- tainly network management schemes and stopgap measures in place to reduce the possibility that a network failure might cause a service inter- ruption, but in a connection-oriented network these measures are exter- nal. Nevertheless, because of its ability to emulate the service provided by a dedicated network, connection-oriented serv