19.4 Light Trail Design

To identify a set of light trails to carry the given traffic is one of the key issues in setting up light trails in a WDM network. The performance of a light trail in terms of wavelength utilization depends upon the locations of the light trail. The goal of the design problem is therefore to develop an effective method of grooming traffic in a light trail architecture and to come up with a set of light trails. The light trail design problem is stated as follows. Given a graph G( V, E) , where V = N, and traffic matrix D _{N N} , define a minimum number of light trails to carry the given traffic.

The design problem is expected to be a hard problem. The approach to identifying a set of light trails to be set up in a network presented here consists of two steps. The first step is called the traffic matrix preprocessing step. As stated earlier, due to the power losses on the lines, a long light trail may not be advisable. The length of a light trail is limited and is specified in terms of the hop length, denoted by Tl _max. A reasonable hop length of a light trail is set to 5. Therefore in the first step, single long-hop traffic is recursively divided into multiple hops.

The second step is to formulate the design problem and to solve it...