Overview

Using the routing techniques of Chapter 3, a path is selected for each demand request entering the network. The next step in the planning process is selecting the regeneration sites for the demand, if any. (Chapter 5 considers techniques for accomplishing routing, regeneration, and wavelength assignment in a single step.) Regeneration cleans up the optical signal, typically by reamplifying, reshaping, and retiming it; this is referred to as 3R regeneration. As discussed in Chapter 3, paths are usually selected to minimize the amount of required regeneration, as regeneration adds to the network cost.

If the network is based on O-E-O technology, then determining the regeneration locations for a selected path is straightforward because the demand is regenerated at every intermediate node along the path. For an optical-bypass-enabled network, where it is possible to transit an intermediate node in the optical domain depending on the quality of the optical signal, determining the regeneration locations for a path may be more challenging. Numerous factors affect when an optical signal must be regenerated, including the underlying transmission technology of the system, the properties of the network elements, and the characteristics of the fiber plant on which the system is deployed. When these factors are considered together, one can estimate the nominal distance over which an optical signal can travel before requiring regeneration (i.e., the optical reach). However, while quoting the optical reach in terms of physical distance is expedient for summarizing the system performance, it is not sufficient for determining the necessary...