On the optimality of packet-oriented scheduling in photonic switches with delay lines

Abstract

Addressing the bandwidth inefficiency problem of current IP over DWDM backbone switching, Optical Packet/Burst Switching (OPS/OBS) provide viable solutions, capitalizing on statistical multiplexing gain, through packet-oriented scheduling. To resolve packet/burst contention, the involved photonic switches contain wavelength converters and fiber delay lines, controlled through a channel and delay selection (CDS) algorithm. Recently proposed CDS algorithms all rely on heuristics, of which the optimality is unexamined to date.<br>&nbsp;&nbsp This paper presents an in-depth analysis of the optimality of CDS algorithms. Methodologically, we rely on Markov chain analysis for performance evaluation, combined with a discrete Markov Decision Process formulation of the optimization problem, optimized for fast calculation, allowing to determine the exact optimum of a specific given setting of the switch, through numerical algebra solution techniques. Results point out that, for the basic switch setting assumed, of all known CDS algorithms, an algorithm called MING (MINimal Gap) is close to optimal, but never strictly optimal. Various graphs support this, showing that an algorithm optimal for any traffic load cannot (in general) be devised. Results for several other switch settings further confirm this, showing how known CDS algorithms might be modified, to attain improved control robustness.