Parallel LSPs for constraint-based routing and load balancing in MPLS networks

Two features of multiprotocol label switching are very useful in network traffic engineering: the path-oriented nature, and the capability to support multiple paths between an ingress-egress node pair. The first feature makes it easy to adaptively route traffic through the network based on the load condition in different parts of the network, while the second feature is often used for load balancing. The role of parallel label-switched paths (LSP) in load balancing and constraint-based routing is investigated. An algorithm named parallel-path-based bandwidth scheme (PPBS) is proposed to make use of parallel LSPs in choosing a bandwidth constraint path. The improvement on flow blocking probability by using PPBS is given quantitatively with respect to the average traffic load on the link, the hops along the path, and the possible number of parallel paths. In conjunction with the PPBS scheme, a feedback-based load-balancing algorithm (FBLB) is proposed to properly distribute traffic onto the parallel LSPs determined by the PPBS. This FBLB algorithm relies on the signalling packets to convey network status information back to the source. Consequently the sources can adjust the traffic distribution into each LSP accurately and promptly. Simulation results show that the FBLB algorithm is simple and effective.