Design of a meta-mesh of chain subnetworks: enhancing the attractiveness of mesh-restorable WDM networking on low connectivity graphs

We have developed a design refinement to increase the capacity efficiency of span-restorable mesh networks on sparse facility graphs. The new approach views the network as a “meta-mesh of chain subnetworks.” This makes the prospect of WDM mesh networking more economically viable than with previous mesh-based designs where the average nodal degree is low. The meta-mesh graph is a homeomorphism of the complete network in which edges are either direct spans or chains of degree-2 nodes. The main advantage is that loop-back-type spare capacity is provided only for the working demands that originate or terminate in a chain and not for the entire flow that crosses a chain. The transiting (“express”) flows are entirely mesh-protected within the meta-mesh graph which is of higher average degree and hence efficiency for mesh restoration than the network as a whole. Nodal equipment savings also arise from the grooming of express lightpaths onto the logical chain-bypass span. Only the meta-mesh nodes need optical cross-connect functionality. Other sites use OADMs and/or glassthroughs. The resultant designs comprise a special class of restorable network that is intermediate between pure span restoration and path restoration. Most of the efficiency of path restoration is achieved, but with a span restoration mechanism which is more localized and potentially faster and simpler than path restoration. The concept lends itself to implementation with OADMs having a passive waveband pass-through feature to support the logical chain bypass spans for express lightpaths.