Buffering of Slow Terminals

A data communications network may be constructed by connecting together terminals and switching nodes so that each terminal is connected to just one node and the nodes are connected together in a more-or-less redundant fashion. All connections are by means of transmission lines. Those between terminals and nodes are called access lines, while those between one node and another are called trunk lines (Fig. 1). For economy, the access lines commonly have smaller bandwidth than the trunk lines. The character of the traffic carried by a data network depends in part upon the type of terminal connected to it. Keyboard and display terminals transmit and receive data messages that are typically less than a few hundred characters in length. These terminals operate at speeds up to 1.2 Kb/s. Batch stations transmit and receive data in larger quantities and typically operate at speeds up to 9.6 Kb/s. Trunk lines, arid the connections to computers, typically operate at about 50 Kb/s. Thus, we find that traffic in a data network is not uniformly distributed either among the terminals or among the various transmission lines. Analysis of delay and the probability of queue overflow is most simply 2865