Feedback Mechanism for MPLS Path Assignment using RSVP-TE

In constraint-based routing a topology database is maintained on all participating nodes to be used in calculating a path through the network. This database contains a list of the links in the network and the set of constraints the links can meet. Since these constraints change rapidly, the topology database will not be consistent with respect to the real network. A feedback mechanism was proposed by Ashwood-Smith, et al, to help correct the errors in the database. They felt that it would be useable only when the database sees the availability of resources to be more than they really are. Gario and Atwood validated this proposal, and showed that the feedback algorithm was helpful in all cases (not only when it was optimistic). Their validation was based on the use of CR-LDP to distribute the MPLS labels. In this paper, we show the same usefulness, for all cases, when RSVP-TE is used to distribute the labels. In addition, because RSVP-TE is a soft-state protocol that requires periodic refresh of its state, the updates that result from the refresh operations provide an additional benefit.