Deterministic protocols for real-time communication in multiple access networks

In a distributed real-rime system, tasks scheduled on different nodes commu nicate by message passing mechanisms. In such a system, where messages are characterized by service times and deadlines, the timely delivery of messag es before their deadlines, is of prime importance. In this article, we cons ider the problem of time-constrained communication over a multiple access n etwork. Prior work in this area has resulted in very few protocols that can bound the worst case channel access time in order to ensure predictability of message transmission. These protocols cannot efficiently support messag es having multiple packets (packet is a basic unit of transmission) which a re needed in most peer-to-peer and client-server real-time applications. As a solution to the problem, we propose best effort protocols based on CSMA/ CD protocol with deterministic collision resolution, that use a concept of message deferment, which is based on laxity (laxity is the maximum amount o f time that the transmission of a message can be delayed). We study the eff ectiveness of the proposed protocols through extensive simulation studies b y comparing them with well known protocols. The simulation results indicate the superiority of the proposed protocols. (C) 1999 Elsevier Science B.V. All rights reserved.