Scalable-distributed-arbitration ATM switch supporting multiple QoS classes

This paper proposes a multi-QoS scalable-distributed-arbitration (MSDA) ATM switch that supports both the high-priority class and the low-priority class under the head-of-line-priority discipline. It has a crosspoint buffer and a transit buffer, each consisting of a high-priority buffer and a low-priority buffer. Arbitration is executed between the crosspoint buffer and the transit buffer in a distributed manner. The MSDA switch extends the advantage of our previously proposed single-QoS scalable-distributed-arbitration (SSDA) switch. It is expandable while permitting high output-line speeds due to the distributed arbitration. The SSDA switch has a problem when its delay-time-based cell selection mechanism is applied to the low-priority class due to the limitation of the number of bits for the delay measure in the cell overhead. We solved this problem by introducing a distributed-ring-arbiter-based cell selection mechanism at each crosspoint for the low-priority class. The low-priority transit buffer at each crosspoint has virtual queues in accordance with the upper input ports. Cells for the low-priority class are selected by distributed ring arbitration among the low-priority crosspoint buffer and the virtual queues at the low-priority transit buffer. Simulations confirm that the MSDA switch ensures fairness in terms of delay time for the high-priority class, while it ensures fairness in terms of throughput for the low-priority class.