PERFORMANCE COMPARISION OF WINDOW AND VIRTUAL TIME PROTOCOLS FOR TIME CONSTRAINED COMMUNICATION

Abstract

Recently, there has been considerable interest in supporting real-time or 'time-constrained communication applications such as packetized voice, distributed sensor networks, and real-time control systems in packet-switched computer communication networks. Various new protocols have been proposed for distributed real-time multiple access networks. In this dissertation real-time traffic requirements for multi access networks has been studied. It has been observed that minimum-laxity-first scheduling policy is optimal for transmitting messages in real-time systems. One of the key issues in implementing a global MLF policy is to determine the message with the minimum laxity in the system. In order to implement the MLF policy, the traditional window protocol is modified so as to base the window on the latest send times of the messages. The latest send time of a message is the time by which transmission of the message must begin if the message is to meet its deadline. The bottom of the window is maintained as the current time and the message that is sent will have its latest send time closest to the current time. This new window protocol has been implemented and compared with the existing virtual time CSMA protocol which also follows the MLF policy for real-time systems. It has been observed that the window protocol performs very well in a wide range of environment and is much better compared to virtual time CSMA/CD protocol most of the time. Simulation has been used to study the performance of these protocols.