Two-step routing for dynamic traffic protection in WDM networks with wavelength continuity constraint

Capacity efficiency is a key issue in designing survivable Wavelength Division Multiplexing (WDM) networks. In this paper, we propose a two-step routing algorithm for dynamic lightpath protection in a WDM mesh network that is subject to wavelength continuity constraint. In other words, upon each call arrival a pair of link-disjoint active and backup lightpaths is to be found for carrying the call. To enhance the capacity efficiency, the resources on the backup lightpath can be shared for protecting different active lightpaths. Owing to the very different natures of active and backup lightpaths, active lightpath is found using the widest-shortest path (WSP) routing and backup lightpath is found using the shortest-widest path (SWP) routing. A distinct feature of our design is that we require both active and backup lightpaths of a call to use the same wavelength. Two major advantages of this feature are: a) source node can use the same laser for both active and backup lightpaths, and b) the scalability issue related to route advertisement is solved. As compared with some existing schemes, we show that our two-step routing algorithm yields noticeably higher capacity efficiency and lower call blocking probability.