A new packet scheduling algorithm for input-buffered multicast packet switches

Head-of-line (HOL) blocking limits the throughput of an input-buffered unicast switch to 0.586. This becomes even more serious for multicast packet switches. In this paper, a packet scheduling algorithm for multicast switches, called Contention-Based Ordering (CBO) algorithm, is proposed. Unlike conventional scheduling algorithms, CBO aims at maximizing the throughput measured at switch output ports, minimizing mean output packet delay, and maintaining a fair access for packets with different fan-outs. To achieve these, a packet compatibility matrix is used to provide the information on packet output contentions. Based on it, the CBO algorithm schedules the packets with the highest contention with others first. The performance of CBO is compared with the previously proposed cyclic-priority reservation (CPR) scheme through simulations. We found that CBO outperforms the CPR algorithm in both throughput, mean packet delay and scheduling fairness. For a 15 x 15 switch with input load p = 0.2 and fan-out probability q = 0.3, a 52% decrease in mean output packet delay and a 6% increase in throughput are obtained as compared to CPR.