Cell versus Message Level Performances in ATM Networks

The goal of this paper is to provide some insight into the relations that exist between cell level and message level performance guarantees in the context of ATM networks. Cell level guarantees are typically what the network is capable of providing, while message level guarantees are the ones of interest to users. It is, therefore, important to understand how the two are related, and which factors influence this relation. There are many different performance measures that are of importance, and in
this paper we try to touch on the (three) most relevant ones. This includes comparing cell and message loss probabilities, average cell and message delays, and cell and message jitter. Specifically, we show that cell and message loss probabilities can exhibit significant differences, which strongly depend on traffic characteristics such as peak rate and burst size, i.e., for a fixed cell loss probability, the message loss probability can greatly vary when peak rate and burst size change. One reason for this sensitivity, is that message loss depends on what happen to {\em all} the cells in a message. For delay and jitter, we also find that peak rate and burst size play a role in determining the relation between cell and message performance. However, this sensitivity is not as acute as with losses since message delay and jitter are typically determined by the performance seen by only {\em one} cell, the last cell in a message. In the paper, we provide quantitative examples that illustrate the range of behaviors and identify the impact of different parameters.