8.6. Summary

In this chapter, we examined signaling for protection and restoration in mesh optical networks. The mesh architecture introduces certain new requirements for protection switching as compared with rings. Chief among these is the need for signaling mechanisms to notify failures and activate the protection path. In this regard, two broad choices for signaling were described: bit-oriented and message-based signaling. The bit-oriented method may have the advantage of speed and simplicity over the message-based method. It is, however, likely that the message-based method may be easier to deploy from an interoperability perspective. The performance of either signaling method in mesh networks is still an area of debate. In ring networks, the 50 ms latency requirement on protection switching is common. In mesh networks, dedicated 1 + 1 type protection switching can be achieved in 50 ms, but shared mesh protection is typically subject to higher latencies (e.g., 200 ms in certain vendor implementations). Message-based signaling in this case may lead to higher latencies than bit-oriented signaling. Another concern with message-based signaling is the possibility of signaling message “storms,” that is, large number of signaling messages generated as a result of failure events, due to the requirement on signaling reliability. It is expected that more insights will be obtained on message-based signaling as studies are performed and deployments occur.