A scheme for QoS control in ATM switching systems

Abstract

This paper concerns with the problem of supporting multiple QoS classes for BISDN services. To support multiple QoS classes, the cell loss rate and cell delay must be able to be controlled. We propose a scheme that can effectively control the cell loss rate and cell delay for each QoS class in an output queueing system. The proposed scheme combines the partial sharing scheme with a static service controller to support multiple QoS classes. Services are categorized into several QoS classes and each class is assigned with a loss-priority and a delay-priority. The buffer space at each output port is logically divided into several nested regions, and higher loss-priority cells can access a larger region to ensure a smaller cell loss probability. Also, the buffer space is physically divided into several queues, and cells of the same delay-priority are stored in the same queue. Higher delay-priOlity cells are served with a higher service rate to ensure a shorter delay. Four traffic classes of combining two different delay and two different loss requirements are considered in the performance evaluation. We have analyzed both the cell loss rates due to buffer overflow and the cell loss rates due to violating the cell delay requirements for all four traffic classes. We have also compared the proposed scheme with the priority assignment control (PAC) scheme which provides a separate queue for each QoS class. These evaluation results show that the proposed scheme is more efficient than the PAC scheme. Moreover, it is even simpler than the PAC scheme, since a less number of queues are needed to be maintained.