PACKET TRAINS - MEASUREMENTS AND A NEW MODEL FOR COMPUTER NETWORK TRAFFIC.

Traffic measurements on a ring local-area computer network at the Massachusetts Institute of Technology are presented. The analysis of the arrival pattern shows that the arrival processes are neither Poisson nor compound Poisson. An alternative model called packet train is proposed. In the packet train model, the traffic on the network consists of a number of packet streams between various pairs of nodes on the network. Each node-pair stream consists of a number of trains. Each train consists of a number of packets going in either direction. The intercar gap is large (compared to packet transmission time) and random. The intertrain time is even larger. The Poisson and the compound Poisson arrivals are shown to be special cases of the train arrival model. The packet arrivals exhibit a source locality which is related to the probability of the next packet being sent between the last node pair which was connected. Implications of the train arrivals and of source locality on the design of bridges, gateways, and reservation protocols are discussed. A number of open problems requiring development of analysis techniques for systems with train arrival processes are also described.