A new class of high speed LAN access protocols based on the principle of timed packet release

This paper describes a class of protocols, based on the principle of Timed Packet Release-or TPR, which provide access to high speed local area network bus structures. The principle behind TPR is a system of time delays in the nodes, reckoned from a common timing reference signal generated at a suitable point on the bus structure. By arranging for the delays in each node to increase according to its physical location on the bus nodes always detect packets from “upstream” nodes before their time delay expires. The TPR protocols described in this paper operate on linear bidirectional and unidirectional buses-although the TPR principle can be realised in a number of versions to provide collision free, prioritised, deterministic access to various bus topologies including hub/star. A comparative evaluation of their performance with established methods of bidirectional bus access such as token passing and the reservation protocols is obtained using discrete event simulation. Performance is measured in terms of the average delay-throughput characteristics of the protocols at data rates extending into the Gigabits/sec. region