Inter-Domain Path Computation using Improved Crankback Signaling in Label Switched Networks

For label switched networks, such as MPLS and GMPLS, most existing traffic engineering (TE) solutions work in a single routing domain. These solutions do not work when a route from the ingress node to the egress node leaves the routing area or the autonomous system (AS) of the ingress node. In such cases, the path computation problem becomes complicated because of the unavailability of the complete routing information throughout the network. We present CWS (computation while switching), a new inter-domain path computation scheme which tries to compute a near-optimal path without assuming the availability of complete topology information. We provide a detailed comparison of the CWS scheme with another per-domain path computation scheme given in J.-P. Vasseur et al. (2006). Unlike the standard per-domain path computation scheme (Vasseur et al., 2006), the CWS scheme continues the quest for a better path instead of terminating the search at the first available path, resulting a significant improvement in terms of path optimality. In particular, CWS guarantees that, for a given network state, a computed inter-domain path will traverse a minimum number of domains. This improvement in path computation directly impacts the amount of traffic that can be allowed on the network. For example, for the COST266 topology with 28 domains and 37 bidirectional inter-domain links, CWS places 960 of the requested 2000 paths as compared to 683 paths placed by existing schemes. Finally, the path setup latency of the CWS scheme remains comparable to that of existing schemes, by allowing the data flow as soon as the first feasible path is found.