Can the introduction of tra c classes improve upon the performance of ATM networks? We investigate this issue within the framework provided by a class of networks that guarantees quality of service. To provide a meaningful comparison we de ne the concept of schedulable region, a region in the space of loads for which the quality of service is guaranteed. We show the dependence of the schedulable region on the scheduling algorithm employed, the quality of service parameters and the tra c statistics. An e cient real-time scheduling algorithm is introduced that substantially increases the schedulable region without incurring prohibitive complexity costs. The schedulable region associated with this algorithm is compared with the ones generated by the static priority scheduling algorithm and a variant of the minimum laxity threshold algorithm. The size and shape of the schedulable region is explored by means of simulations.

A framework for joint scheduling and admission control in broadband switching systems is developed according to a principle of separation between these two levels of control. It is shown how an admission control strategy can be tailored to a particular mix of tra c by making use of high-level information from the scheduler. This principle is presented in the context of Asynchronous Time-Sharing (ATS), in which explicit guarantees of cell-level and call-level quality of service (QOS) are given to several tra c classes. The separation principle allows the formulation of an optimal admission control policy, which will maximize the expected system utility while maintaining all QOS guarantees. Several heuristic admission control policies are considered, and compared against the optimal policy as a benchmark. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time tra c are used to illustrate the e ects of di erent scheduling and admission control policies on both the expected utility and the admissible load region.

A joint scheduling and admission control algorithm is presented for Asynchronous Time-Sharing (ATS)-based switching nodes carrying real-time traffic. Systems based on ATS guarantee quality of service, at both the levels of cells and calls, for three well-defined traffic classes. A mechanism is outlined by which an admission control strategy can be tailored to a particular mix of traffic classes. A mechanism is outlined by which an admission control strategy can be tailored to a particular mix of traffic by making use of high-level information from the scheduler. This mechanism is based on a principle of separation between scheduling and admission control. A linear programming formulation is used to find the admission control policy which will maximize the expected system utility while maintaining the guaranteed quality of service. The admissible load region is introduced as a means of quantifying the capacity of a switch under the QOS constraints at the cell and call levels. Numerical calculations for a single MAGNET II switching node carrying two classes of real-time traffic are used to illustrate the effects of different scheduling and admisssion control policies on both the expected utility and the admissible load region.

No abstract

No abstract