Overview

Wavelength assignment is an integral part of the network planning process in optical-bypass-enabled networks. Its need arises from the wavelength continuity property of optical-bypass elements, where a connection that traverses a node alloptically must enter and exit the node on the same optical frequency. Thus, the wavelengths that are in use on one link may have ramifications for the wavelengths that can be assigned on other links. Effective wavelength assignment strategies must be utilized to ensure that wavelength contention is minimized.

Wavelength assignment is tightly coupled to the routing process, as the selection of the route determines the links on which a free wavelength must be found. The two processes are often referred to together as the routing and wavelength assignment (RWA) problem. However, regeneration, when needed, is just as critical to the process. While the earliest visions of optical-bypass-enabled networks assumed that they would be completely all-optical, with no regeneration, this has not turned out to be the case in reality, especially in regional and backbone networks. The presence of regeneration has a significant impact on wavelength assignment because it allows for a change in wavelength. This is explored in Section 5.1.

The previous two chapters looked at the sequential processes of selecting a route followed by selecting regeneration locations. Wavelength assignment can be treated as the third sequential step in the planning process. With this multi-step approach, there is no guarantee that the route found will be amenable to a feasible wavelength assignment. Another option is to...