No abstract

This paper describes the operation of a proposed method of access to bidirectional local area network buses - called Timed Packet Release or TPR. The method is based on a system of time delays in the nodes, reckoned from a timing reference signal and provides collision free deterministic access for queued packets. A comparative evaluation of the performance of TPR with other methods of bi-directional bus access such as token passing and the reservation protocols is provided. Results, obtained using discrete event simulation models, are presented for the various access protocols. Performance is measured in terms of the average delay-throughput characteristics of the networks. The implementation aspects of TPR are reviewed briefly

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 gelrerated 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 deslcribed in this paper operate on linear bidirectional and unidirectional buses -athough the TPR principle can be realised in a number of versions to provide collision free, prioritised, deterministic access to various bus topologies including hubistar. 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 Cigabitslsec. region. 1: IntroductionThe development of high speed data transmission techniques over optical fiber in the 1980's led to the emergence of high speed LANs, firstly with data rates of 1OOMbps. but now stretching into the Gigabits/sec. region. Initially, thereforc, most proposals for access protocols for high speed LANs and MANS were based on access methods that were only suitable for use with unidirectional interconnecting structures, such as unidirectional buses and rings.More recently the development of high spced data transmission techniques over copper, has led to the development of a number of 1OOMbps. LAN solutions based on long established methods, such as CSMPKD 111 and token passing [2,3], as well as those based on the new hub based Demand Priority polling mechanism [4].As data rates are incrcascd the extra propagation delays of star (hub) structures bccome significant. This paper tlherefore introduces two new protocols which provide deterministic access to linear buses. The paper primarily describes their operation over bidirectional linear buses although operation over unidirectional bus topology is also described -as it currently supports the highest data rates. Both protocols are based on the principle of Timed Packet Release, or TPR. TPR uses a system of appropriately chosen time delays in each node, reckoned from a common timing reference signal, generated by a Monitor node, to ensure collision free transmission of data packets. The performance characteristics of the various proposals are reviewed in the context of each other and of previously proposed deterministic access methods. In the case of the bidirectional linear bus, in particular, it is shown how TPR overcomes many of the performance limitations imposed on traditional access methods by the broadcast nature of the bus. Performance figures at 100Mbps. and 1.6Gigabits/sec. are presented. 2: The effects of signal propagationThe design...

No abstract

No abstract