Minimum Delay Scheduling in Scalable Hybrid Electronic/Optical Packet Switches

A hybrid electronic/optical packet switch consists of electronically buffered line-cards interconnected by an optical switch fabric. It provides a scalable switch architecture for next generation high-speed routers. Due to the non-negligible switch reconfiguration overhead, many packet scheduling algorithms are invented to ensure performance guaranteed switching (i.e. 100% throughput with bounded packet delay), at the cost of speedup. In particular, minimum delay performance can be achieved if an algorithm can always find a schedule of no more than N configurations for any input traffic matrix, where N is the switch size. Various minimum delay scheduling algorithms (MIN, alpha(i)-SCALE and QLEF) are proposed. Among them, QLEF requires the lowest speedup bound. In this paper, we show that the existing speedup bound for QLEF is not tight enough. A new bound which is 10% lower than the existing one is derived.