A highly efficient path-restoration protocol for management of optical network transport integrity

Distributed path restoration based on optical cross-connects can provide hi ghly capacity-efficient real-time restoration for WDM-based optical network ing. However, to obtain an assured restoration level with the theoretically very low amounts of spare capacity that path restoration allows, one must solve, or closely approximate a solution to, the integer multicommodity max imum flow (MCMF) problem. MCMF is, however, a hard combinatorial optimizati on problem due to what is called the "mutual capacity" aspects of the probl em: which of many competing origin-destination pairs should be allowed path s over the finite spares on each span? Integer MCMF is further complicated by the nonunimodular nature of the problem, i.e,, fractional flows are forb idden but would arise if solved by Linear Programming. This paper presents a heuristic principle that tests well against Integer Programming solutions of MCMF routing. The heuristic is first characterized in a centralized pro gram, then adapted for use in a distributed path restoration protocol. In a ll test cases, the protocol obtains over 97% of the paths found in an optim al MCMF solution in the same network. Via OPNET simulation it is also predi cted that the protocol will run in well under 2 seconds which means it coul d be used directly in real-time, or in distributed prefailure self-planning , for restoration. The significance is that network operators could aggress ively optimize their spare capacity, toward theoretical minimums, while sti ll assuring 100% restorability.