Abstract

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. It behaves like a depth first search, and is meant to be useable only when the database sees the availability of resource more than there really are. In this mechanism, the source node can learn from the successes or failures of its path selections by receiving feedback from the path it is attempting. The received information is used in the subsequent path calculations. We validated the feedback algorithm to see how it behaves in all database situations, and found out that the feedback algorithm was helpful in all cases not only when it was optimistic. We also propose adding query messages to make the feedback algorithm behave more like breadth first search. The path query messages algorithm reduces the retry attempts in setting up a path, and also utilizes the network by gathering much more information about the resources.