Optimizing Partially Ordered Transport Services for Multimedia Applications

References [1, 5] introduce a transport protocol that o ers partially ordered service for multimedia applications. This paper investigates how much the selection of a linear extension a ects system performance in a partially ordered service. We rst show how to identify better linear extensions of a partial order, and then determine the performance gains by using such linear extensions at the time of transmission. To quantify linear extensions of a partial order, we propose a new metric (pBuf -metric) that is derived from bu ering probabilities. Since pBuf -metric is complex to calculate, a simpli ed version called -metric is also investigated. An OPNET simulation shows that for certain partial orders, a linear extension optimized according to these metrics provides some delay, and signi cant bu er utilization improvements over a non-optimal linear extension. Thus, prudent transmission order selection in a partially ordered service does improve system performance. Results also show that, in general, -metric is as e ective as pBuf -metric in identifying better linear extensions of a partial order.