Evaluating scheduling in integrated-services networks using a semi-fluid-flow model

Abstract

An integrated?services network carries diverse traffic, which leads to diverse performance objectives. For example, voice and video packets typically have performance objectives based on the fraction of packets that will be delivered within a given delay bound, while data packets often have objectives based on mean delay. Greater loads can be supported in networks in which a voice or video packet is given priority over data packets if and only if the former is in danger of missing its deadline. Algorithms that allow this include Cost?Based Scheduling, occupancy?based algorithms, the Priority Token Bank, and to a lesser extent, the Leaky Bucket. This paper presents an approach to evaluating performance with these algorithms in the realistic case where data arrivals are highly bursty, but voice and video packets are not. Mean queueing delay for data bursts is determined analytically in some important scenarios, and an efficient simulation approach based on the same model is described for cases where analysis is not currently possible. The model is a semi?fluid?flow model in which voice or video packets are assumed to arrive as a continuous fluid flow, whereas data packets arrive in large bursts at discrete instants in time.