Chapter 8 - GMPLS and Service Recovery

Abstract

There are numerous ways to classify failures within transport networks. Depending on the type of failed network element, the failures can be broken into two groups that include control plane failures, and data plane failures. Further, depending on the type of a failed component, the failure can be classified as a hardware (electronic or optical component defect), software (bug), or configuration (operator mistake) failure. Two different levels of recovery are identified depending on the object of protection such as TE link or service path, which include link level recovery (also referred to as span recovery), and path level recovery. In the case of span recovery, all services traversing a particular span are protected against any failure detected on the span. Specifically, when the span fails, allspan-protected services are switched simultaneously onto some other parallel span. In the path level recovery model each protected service is recovered from a failure independently. It means that if some failure affects multiple services, the failure is indicated separately for each of them, and multiple fault notification messages are sent to different deciding entities located on different nodes, which trigger independent recovery operations. Enhanced span protection is defined as any protection scheme that provides better (more reliable) span protection than dedicated 1 + 1 span protection. One of the types of enhanced span protection is the four-fiber SONET BLSR ring.