The preplanned weighted restoration scheme

One of the expected benefits of Wavelength Division Multiplexing (WDM) is the possibility to provide an optical layer (OL) with built-in capabilities to survive to network component faults, e.g., fiber cut. Several schemes exist to design a reliable OL. These schemes are generally divided into protection and restoration techniques. Protection schemes reserve in advance a dedicated backup path and a wavelength that are readily available upon disruption of the working path. Restoration schemes, on the contrary, dynamically look for backup paths of spare wavelengths upon failure occurrence. While protection schemes have been extensively used in the telephone industry for many years due to their prompt reaction to faults, restoration schemes are preferred candidates for the OL as, in principle, they yield more efficient and flexible resource reservation. The latter schemes, however, typically require a relatively long time to be completed due to the heavy signalling that originates upon network failure. In high capacity WDM networks, the presence of many connections concurrently seeking restoration exacerbates the above problem as, in existing restoration schemes, coordination among restoration attempts may further slow down the process completion. The authors propose a fast and efficient path restoration scheme called Preplanned Weighted Restoration (PWR). In the PWR scheme distinct restoration paths are precomputed at the source node during the connection setup. Upon failure, one of the preplanned paths is randomly selected depending on specific weights precalculated by the source node. The proposed scheme requires limited signaling upon failure occurrence as coordination among the source nodes involved in the restoration process is not required. Therefore, the scheme is fast and scalable in terms of number of network nodes,link or fiber capacity, and number of connections. Yet, presented results show that the PWR scheme may considerably decrease the blocking probability of the restoration attempts when compared to other schemes such as the alternate routing.