Capacity Efficient Distributed Routing of Mesh-Restored Lightpaths in Optical Networks

A mesh-restored lightpath in an optical network has a primary route and a diversely routed backup route. The wavelength channels on the primary route of a mesh-restored lightpath are dedicated for that lightpath whereas the wavelength channels on the backup route are shared among different mesh-restored lightpaths. Wavelength channels are shared in a way that ensures restoration of all lightpaths affected by any single link failure. In the centralized scenario, complete knowledge of the network state allows determination of the sharability of a backup channel during path computation. This information is not available in the distributed scenario. Use of 1+1 routing algorithms for mesh-restored lightpaths leads to inefficient capacity sharing. We propose distributed routing techniques to decrease the capacity efficiency gap between centralized routing and 1+1 routing of mesh-restored lightpaths. The algorithm uses information about the number of available and (shared) backup channels in a link, which can be disseminated through traffic engineering extensions to OSPF. A sharing database at each OXC maintains information about the lightpaths whose primary or backup paths traverse that OXC. The approach involves distributed determination of the sharability of a link on the backup path during path signaling using the sharing database at each OXC on the backup path. This, combined with a retry scheme facilitated by crankback routing extensions to CR-LDP/RSVP-TE to reduce lightpath blocking, leads to capacity efficient distributed routing of mesh-restored lightpaths.