Decentralized Local Backup LSP Calculation with Efficient Bandwidth Sharing

This paper focuses on the protection of virtual circuits (Label Switched Paths, LSPs) in a (G)MPLS [1] (Generalised Multi-Protocol Label Switching) network. The proposed algorithm is designed to protect traffic with strong delay requirements such as EF (Expedited Forwarding) ordered aggregates in a DiffServ domain. For this type of application endto-end recovery schemes are usually considered to be far too slow. Local, fast-rerouting is the only solution which can compete with restoration times offered by SONET self-healing ring. However local restoration has a cost in terms of extra bandwidth consumed for the backup paths. Our scheme thus includes a sophisticated resource aggregation mechanism based on the concepts of “backup-backup aggregation” and “backupprimary aggregation”. The path selection algorithm is also designed to efficiently reduce the resource usage. Moreover, when considering LSPs at different preemption levels, our algorithm is able to correctly calculate the amount of bandwidth that can be preempted despite the sharing of resource. We show that our approach, though local, can compete with the state-of-theart end-to-end recovery schemes (such as the one presented in [2]) in terms of resource reservation. The major contribution of our scheme, the “backup-primary aggregation”, was then also used in the context of end-to-end recovery and improved its performance substantially.