Multislot scheduling algorithm in ATM networks

A key implementation issue of multicast switching systems is the reduction of cell conflicts which occur when two, or more, cells approach for the same link, internal link or output link, simultaneously. When a cell conflict occurs, only one of the contending cells is allowed to access the link and the others are dropped or stored in internal buffers. The cell contention is the basic reason that the switch throughput drops. Several contention resolution schemes have been proposed. Each input port is associated with a tag queue for storing a routing text of arriving cells, and a cell-scheduling controller is provided to resolve the output contention problem according to the HOL (head-of-line) entries of tag queues. The proposed algorithm differs from previous algorithms in that we consider the output contention resolution for multiple slots instead of only the current time slot. Like a window based scheduling algorithm, our algorithm allows cells behind an HOL cell to be transmitted prior to the HOL cell in the same input port. Thus, HOL blocking can be alleviated. The delay throughput performance of our algorithm outperforms most of those algorithms that consider the output contention resolution only for the current time slot.