Chapter 9 - Network Survivability

Abstract

Engineering the network for survivability is an important role in transport networks. To obtain full availability of the network is to make the network survivable, that is, able to continue providing service in the presence of failures. Protection switching is the key technique used to ensure survivability. These protection techniques involve providing some redundant capacity within the network and automatically rerouting traffic around the failure using this redundant capacity. Protection techniques are well established in SONET and SDH, and include point-to-point, dedicated protection rings, and shared protection rings. These protection techniques are used or are being developed in other networks in the client layer. Point-to-point protection schemes work for simple systems with diverse fiber routes between node locations. Dedicated protection rings are used primarily to aggregate traffic from remote locations to one or two hub locations. Shared protection rings can be used in the core parts of the network, where the traffic is more distributed. Optical layer protection is needed to protect the data services that are increasingly being transported directly on the optical layer without the SONET/SDH layer being present. Optical channel layer protection is needed if some channels are to be protected while others are not. Optical multiplex section layer protection is more cost-effective for those cases where all the traffic needs to be protected. Shared mesh protection in the optical layer can lead to more bandwidth efficiency and flexibility compared to traditional ring-based approaches.