HOPSMAN: An Experimental Optical Packet-Switched Metro WDM Ring Network With High-Performance Medium Access Control

Future optical metropolitan area networks (MANs) have been expected to exploit advanced optical packet switching (OPS) technologies to cost-effectively satisfy a wide range of applications having time-varying and high bandwidth demands and stringent delay requirements. In this paper, we present the architecture and access control of our experimental high-performance OPS metro WDM slotted-ring network (HOPSMAN). HOPSMAN has a scalable architecture in which the node number is unconstrained by the wavelength number. It encompasses a handful of nodes (called server nodes) that are additionally equipped with optical slot erasers capable of erasing optical slots resulting in an increase in bandwidth efficiency. In essence, HOPSMAN is governed by a novel medium access control (MAC) scheme, called probabilistic quota plus credit (PQOC). PQOC embodies a highly efficient and fair bandwidth allocation in accordance with a quota being exerted probabilistically. The probabilistic quota is then analytically derived taking the server-node number and destination-traffic distribution into account. Besides, PQOC introduces a time-controlled credit for regulating a fair use of the remaining bandwidth, particularly in the metro environment with traffic of high burstiness. Extensive simulation results show that HOPSMAN with PQOC achieves exceptional delay-throughput performance under a wide range of traffic loads and burstiness.

I. Introduction

For long-haul backbone networks, optical wavelength division multiplexing (WDM) [1] has been shown to be successful in providing virtually unlimited bandwidth to support a large amount of steady traffic based on the optical-circuit-switching (OCS) paradigm. Future optical metropolitan area networks (MANs) [2], [3], on the other hand, are expected to cost-effectively satisfy a wide range of applications having time-varying and high bandwidth demands and stringent delay requirements. Such facts bring about the need of exploiting the optical-packet-switching (OPS) [3], [4] paradigm that takes advantage of statistical multiplexing to efficiently share wavelength channels among multiple users and connections. Note that the OPS technique studied here excludes the use of optical signal processing and optical buffers, which are current technological limitations OPS faces. Numerous topologies and architectures [2]–[11] for OPS-based WDM metro networks have been proposed. Of these proposals, the structure of slotted rings [5]–[12] receives the most attention. Essentially, these slotted-ring networks offer high-performance access and efficient bandwidth allocation by means of medium access control (MAC) schemes [2].