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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.

Absrracr-Multiprotocol Label Switching (MPLS) technology provides efficient means for controlling the traffic of IP backbone networks and thus, offers performance superior to that of traditional Interior Gateway Protocol (IGP) based packet forwarding. However, computation of explicit paths yielding optimal network performance is a difficult task; several different strategies can be thought of. In this paper we propose a novel approach for the optimal routing of new label switched paths (LSPs).Our method is based on the idea that we allow the re-routing of an already established LSP when there is no other way to route the new one. Our optimization algorithm is based on an Integer Linear Programming (ILP) formulation of the problem. We show by numerical evaluation that our method significantly improves the success probability of setting up new LSPs by extending the widely known Constrained Shortest Path First (CSPF) algorithm with the ILP-based re-routing function. Although the task itself is NP-hard, our heuristic method provides efficient solution in practical cases. The proposed algorithm is aimed to be implemented primarily in a network operation center. However, with the restriction that only LSPs starting from the optimizing Label Edge Routers can be rerouted, the algorithm can be implemented directly in edge routers themselves in a distributed fashion.

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