Deterministic protocols real-time communication in multiple access netowrks

摘要

In a distributed real-time system, tasks scheduled on different nodes communicate by message passing mechanisms. In such a system, where messages are characterized by service times and deadlines, the timely delivery of messages before their deadlines, is of prime importance. In this article, we consider the problem of time-constrained communication over a multiple access network. 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 messages having multiple packets (packet is a basic unit of transmission) which are 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 of time that the transmission of a message can be delayed). We study the effectiveness of the proposed protocols through extensive simulation studies by comparing them with well known protocols. The simulation results indicate the superiority of the proposed protocols.