Dynamic Queue Length Thresholds for Multipriority Traac

Buuer management schemes are needed in shared-memory ATM switches to regulate the sharing of memory among diierent output port queues and among traac classes with diierent loss priorities. Earlier we proposed a single-priority scheme called Dynamic Threshold, in which the maximum permissible queue length is proportional to the unused buuering in the switch. In this paper, we propose and analyze four diierent ways of incorporating loss priorities into the Dynamic Threshold scheme. The analysis models sources as deterministic uids. Output port loads may consist of any mixture of loss priorities, and these loads may vary from port to port. We determine how each scheme allocates buuers among the competing ports and loss priority classes, and we also note how this buuer allocation induces an allocation of bandwidth among the loss priority classes at each port. We nd that minor variations in the Dynamic Threshold control law can produce dramatically diierent resource allocations.