Improving service availability In ERP based mesh networks

Ethernet Ring Protection (ERP) has recently emerged to provide protection switching for Ethernet ring topologies with sub-50 ms failover capabilities. In addition to Ethernet's cost-effectiveness and simplicity, ERP's promise to also provide protection in mesh packet transport networks positions Ethernet as a prominent competitor to conventional SONET/SDH and the technology of choice for carrier networks. Higher service availability, however, in ERP has been challenged by the issue of network partitioning caused by concurrent failures. In this paper, we show that in a network designed to withstand only single failure situations, the service availability in the presence of dual failures is affected by the design method, i.e., the RPL placement as well as the selection of ring hierarchy. Therefore, we present a study for characterizing service outages and propose a design method which strikes a balance between capacity requirement and service availability (i.e., the number of service outages resulting from concurrent failures). We observe that by properly selecting the RPL positions and the ring hierarchies, remarkable reduction in service outages is obtained (hence higher service availability in the presence of dual failures) at a modest increase in capacity deployment. Numerical results show that our design approach can reduce the number of service outages as much as 39.1% with only 6.9% additional investment in capacity deployment.