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Abstract-The hose resource provisioning model promises to provide an easy-to-use characterization framework for Virtual Private Network service offerings. Significant research effort has recently been spent on proposing new algorithms for provisioning cost-optimal networks specified according to this new model. However, a detailed comparison of the bandwidth requirement for networks designed based on the hose model and networks designed based on the traditional pipe model has not been performed. The first contribution of this paper is a detailed comparison of the bandwidth needs of the two models assuming a range of network sizes and network topologies. This numerical evaluation required efficient calculation methods for determining resource allocation based on the hose model parameters, therefore, a linear programming based formulation is also presented for this purpose. The second contribution is the calculation of a lower bound for the hose based realization. This lower bound is very useful in evaluating the two models given that the problem of provisioning a minimal cost network based on the hose model specification can only approximately be solved in polynomial time.

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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.