TABLE OF CONTENTS Control and data planes in transport networks are separated so that control plane messages do not necessarily flow along the links they control. One of the consequences of this is that the two can fail independently. Let us consider the following cases in respect to the relationship between control and data plane failures of a particular LSP.
Control plane is functional on all nodes; data plane failures are detected on one or more nodes.
Control and data planes fail at the same time on one or more nodes.
No data plane failures are detected (that is, user traffic is not affected); control plane fails on one or more nodes.
Control and data planes fail on different nodes.
So far in this chapter we have considered only case 1. We implicitly assumed that once a failure is locally detected, the FIS message is delivered to the appropriate PLR/MN, which uses the synchronizing signaling to perform the protection switchover operation, computes and signals a new path disjoint from the point of failure, or tears down the affected LSP. These assumptions require the control plane to function on all nodes of the protected and protecting LSPs.
Case 2 might seem a difficult one, but in fact it is not. If the data plane on a node fails, traffic of a service traversing the node is affected. Hopefully, the neighboring nodes detect the failure and the traffic is switched away from the failed node. Note that the failed node itself...
