Pipelining multicast scheduling in all-optical packet switches with delay guarantee

In this paper, we study multicast scheduling in all-optical packet switches. First, we propose a novel optical buffer called multicast-enabled Fiber-Delay-Lines (M-FDLs), which can provide flexible delay for copies of multicast packets using only a small number of FDL segments. We then present a Delay-Guaranteed Multicast Scheduling (DGMS) algorithm that considers the schedule of each arriving packet for multiple time slots. We also discuss some desirable features of DGMS in detail, such as guaranteed delay upper bound and adaptivity to transmission requirements. To relax the time constraint of DGMS, we further propose a pipelining technique that distributes the scheduling tasks among a sequence of sub-schedulers. The combinatorial logic circuit design of each sub-scheduler, which further reduces time complexity, is also provided. The performance of DGMS is tested extensively against statistical traffic models and real Internet traffic, and the results show that the proposed DGMS algorithm can achieve ultra-low average packet delay with minimum packet drop ratio.

I. Introduction and Related Work

Optical networking has been widely adopted to transport high volume traffic in backbone networks due to the huge bandwidth of optics. All-optical packet switches are considered as a very appealing solution for high-throughput, energy-efficient and transparent forwarding in backbone networks. During the past few years, as driven by the increasing multicast applications requiring high-bandwidth transmission from one source to multiple destinations, such as video conference, video-on-demand (VoD) and IP-based Television (IPTV) [1], [2], optical multicast packet switching has attracted much research effort. A series of all-optical switching architectures and technologies have been proposed to support multicast at the switch/router level, such as wavelength-assisted switching [4], [13], Broadcast-and-Select (BS) switching [3], [9], etc. Despite of the considerable amount of work on multicast-capable optical packet switching architectures, however, relatively little attention has been paid on multicast scheduling in such switches, which is critical for high-speed all-optical packet switches. Motivated by this observation, in this paper we consider multicast scheduling in optical packet switches.