Performance of scalable-distributed-arbitration ATM switch supporting multiple qos classes

A multi-QoS scalable-distributed-arbitration (MSDA) ATM switch is described that supports both high- and low-priority traffic under the head-of-line-priority discipline. It uses crosspoint and transit buffers, each consisting of a high- and low-priority buffer. The buffers arbitrate in a distributed manner the selection of which cellsto transmit. The MSDA switch supports multiple QoS classes 'while still providing the scalability of a previously described single-QoS scalable-distributedarbitration (SSDA) switch. A problem occurs when the delaytime-based cell-selection mechanism used in the SSDA switch is applied to the low-priority traffic: it cannot achieve fairness in terms of throughput. This problem is overcome by introducing a distributed-ring-arbiter-based cell-selection mechanism at each crosspoint for the low-priority traffic. The low-priority transit buffer at each crosspoint has virtual queues, one for each upper input port. Cells for the low-priority traffic are selected by distributed-ring arbitration among the low-priority crosspoint buffer and these virtual queues. For the high-priority traffic, the same delay-time-based cell-selection mechanism is used as in the SSDA switch. Simulations show that the MSDA switch ensures fairness interms of delay time for the high-priority traffic and ensures fairness in terms of throughput for the low-priority traffic.