In Chapter 5 we discussed shared-channel networks, and the emphasis was on satisfying traffic requirements on a static, multipoint physical topology (a broadcast star or its equivalent). The traffic requirements were expressed in terms of flows on logical connections (LCs), and satisfaction of these requirements involved multiplexing and multiple access to share the available channels efficiently. When combined time and wavelength division techniques were employed, the optical connections supporting the LCs were set up and time shared by rapidly tuning the transceivers over a given set of wavelengths. Because all optical connections shared a common broadcast medium in a static configuration, all optical paths supporting these connections were permanently in place. We now move on to optical connection routing and wavelength/waveband assignment – issues that were absent in the static case. We treat both point-to-point and point-to-multipoint (multicast) logical connections.

Introduction

In this chapter we focus on the optical layer of the architecture shown in Figure 2.1(a); that is, we treat purely optical (transparent) networks with reconfigurable optical paths, in which reconfiguration is achieved by space switching together with wavelength and/or waveband routing. Unless otherwise stated, we assume that there is no wavelength conversion in these networks, so the constraint of wavelength continuity is in force. The earliest proposals for wavelength-routed networks (WRNs) appeared in [Brain+88] and [Hill88].

In much of the subsequent work on these networks, a recurring issue has been to determine the number of wavelengths required to achieve a desired degree of connectivity as a function of network size and functionality of network nodes (e.g., static wavelength routers, static wavelength interchangers, or WSXCs).