Balazs Szviatovszki

Inverse optimization in high-speed networks

A general approach is presented for handling the following inverse optimization problem: given solutions to each member of a family of combinatorial optimization tasks on a common underlying set, find a positive linear objective function (weighting) on the common underlying set that simultaneously makes each solution optimal in its own optimization task. Our motivation stems from the inverse shortest path problem that is made practically important in high-speed telecommunication networks by the Asynchronous Transfer Mode Forums Private Network-Network Interface architecture, in which route finding can be based on administrative weights. Different variants of the problem are investigated, including uniqueness requirements and reserve routes.

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

In this paper, we study the effect of distributed constrained shortest path first (CSPF)-based path selection on the dynamics of label switched path (LSP) preemption. We propose new CSPF algorithms for minimizing preemption of lower priority LSPs without requiring any enhancements to the recently proposed link-state parameters. 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 while the LSP setup success ratio is basically the same for all methods.

Prompt partial path optimization in MPLS networks

In this paper we evaluate approaches that allow the re-routing of a set of already established label switched paths (LSPs) in multiprotocol label switching (MPLS) networks when a new LSP demand faces constrained shortest path first failure. Two optimization algorithms are proposed: one is based on an integer linear programming formulation of the problem, while the other one is a heuristic method based on Dijkstras shortest path first algorithm: We analyze the efficiency of our algorithms in a dynamic network environment. The simulation experiments show that our method significantly increases the total network throughput. We also investigate the limitations of the applicability of proposed methods considering their running time.

Analysis of link cost functions for PNNI routing

Abstract The emerging environment of ATM networks with unpredictable traffic patterns and ever-changing network configurations create the need for using dynamic routing methods. Dynamic routing basically means that path selection continuously adapts to the state of the network. The routing framework of the Private Network-to-Network Interface (PNNI) specification achieves this by using link-state information gathered from the network. One possible approach for selecting paths is to use a shortest path algorithm (e.g., Dijkstras) with link costs generated from the link load information. This mapping is realised by the so-called link cost function. We investigated a number of such link cost functions with simulation. We developed two novel link cost functions and compared them with those found in the literature. The primary basis of comparison was the total throughput of the networks. Besides this, we also investigated such issues as imposed signalling load and robustness.

On the use of trunk reservation in PNNI routing

We investigate how alternate routing and trunk reservation can be used in the private network-network interface (PNNI) framework to enhance the routing performance of ATM networks. After determining the optimal trunk reservation parameters we show, that alternate routing with trunk reservation is superior to both direct routing and simple alternate routing under most traffic conditions. We also show that the current PNNI framework does not allow for fully exploiting the advantages of the trunk reservation concept. Simulation studies performed on a large number of randomly generated networks show that the combination of alternate routing and trunk reservation can provide an efficient and robust routing algorithm.