Minimizing re-routing in MPLS networks with preemption-aware constraint-based routing

The importance of providing bandwidth guarantees in packet backbone networks is increasing with the emergence of virtual private networks and mobile networks, where bandwidth requirements of aggregate packet flows with diverse characteristics have to be supported. Both in VPNs and in mobile networks traffic will be prioritized to support preemption of less important traffic. The Multiprotocol Label Switching architecture addresses both traffic prioritization and bandwidth guarantees. A proposed way of doing path selection in MPLS is based on constrained shortest path first (CSPF) methods. In this paper, we study the effect of distributed CSPF based path selection on the dynamics of LSP preemption in MPLS networks. We propose new CSPF algorithms that aim at minimizing preemption of lower priority LSPs and thus enhance the stability of multi-priority MPLS networks, without requiring any enhancements to the recently proposed link-state parameters. Since in a distributed environment where only summarized information is available exact methods can not be developed, our algorithms provide different polynomial heuristic methods for the preemption minimization problem. The difference between priority-based path selection methods and previously proposed CSPF methods lies in the way the selection is done among equal cost shortest paths. Our priority-aware CSPF algorithms decrease the number of preempted lower priority LSPs, thus result in less re-routing in the network, while the LSP setup success ratio is basically the same for all methods.