Observations on a class of rate-based schedulers

The method of packet scheduling employed in a communications network is crucial to the delivery of real-time services with adequate quality of service. In particular, specified amounts of service must be provided to each session before set time instants, and an upper bound on packet delay must be satisfied by each session. This paper identifies properties of two important groups of schedulers. These properties relate to the slope of the associated virtual time function. We show that within each group, there are similar bounds on the delay caused by each scheduler, although the schedulers may service the same packets in a different order. We introduce the concepts of start time and finish time schedulers. It is found that start time schedulers have delay bounds that are not dependent on session rate, while finish tune scheduler delay bounds have this dependency. Based on these results, general observations are made on the behaviour of rate-based schedulers with respect to the service they provide and the maximum delay they introduce.