Static versus dynamic establishment of protection paths in WDM networks

In wavelength division multiplexed networks (WDM) with 1:1 path protection, a link-disjoint protection (backup) path is also set up at the time of setting up a working (primary) path. Hence, the failure of a single fiber-link does not cause huge data losses. This paper considers on-line routing and wavelength assignment (RWA) of protection paths in such networks. In particular, we study two strategies based on the 1:1 path protection scheme. The Static strategy establishes protection paths such that once a route and wavelength have been chosen they are not allowed to change. On the other hand, the Dynamic strategy allows for re-arrangement of protection paths, that is, both the route and wavelength chosen for a protection path can change so as to accommodate a new request. With either strategy, we assume that the working paths cannot be re-arranged. This is to prevent the disruption of on-going traffic. The two strategies are compared on the basis of the number of connections requests that can be satisfied for a given number of wavelengths, assuming that the requests come one at a time, and wavelengths are assigned according to the First-Fit policy. One of the results of our study is that, contrary to intuition, the Static strategy performs better than the Dynamic strategy.