Andras Farago

Efficient routing of lightpaths

A routing solution is presented to find optimal routes for lightpaths and for the new concept of semi-lightpaths. A lightpath is a fully optical transmission path, while a semi-lightpath is a transmission path constructed by chaining together several lightpaths, using wavelength conversion at their junctions. A fast and practical algorithm, with proven optimal speed, is presented to optimally route lightpaths and semi-lightpaths taking into account both the cost of using the wavelengths on links and the cost of wavelength conversion.

Enhancing ATM Network Performance by Optimizing the Virtual Network Configuration

Virtual or logical subnetworks are expected to play an important role in large B-ISDN configurations. This gives an additional degree of freedom to ATM network architectures, since even for a fixed physical network the logical configuration can still vary depending on particular demands and conditions. This new degree of freedom calls for new solutions to utilize the opportunity for the potential enhancement of network performance by optimizing the logical configuration, as part of optimizing the distributed network architecture. In this paper a framework and model, along with efficient solution algorithms, are presented to dimension virtual ATM networks on top of the same physical infrastructure network, such that the virtual networks share the infrastructure, while the total network revenue is optimized. The algorithms are tried on various network scenarios and a trade-off between the quality of the result and running time is exhibited.

A fundamental relationship between fairness and optimum throughput in TDMA protocols

A general relationship is established between fairness and throughput in TDMA protocols. We prove the fundamental result that, under quite general conditions, fairness and optimum throughput imply each other in TDMA protocols, in the sense that if one of them holds then the other is automatically guaranteed to hold. The result has the important practical consequence that in cases when packet loss is characterized by a loss function, satisfying certain natural properties, it is enough to guarantee fairness to automatically obtain a guaranteed maximum throughput. Or, conversely, maximum throughput will automatically lead to fairness.

Simulation Analysis of Routing Strategies in Multicasting Multiservice Loss Networks

This paper begins with an overview of multicast algorithms, which are the most promising candidates to be in wide use in first generation Asynchronous Transfer Mode (ATM) based Broadband Integrated Services Digital Networks (B-ISDN). Since the Multiple Destination Routing (MDR) problem and the associated Steiner Tree problem are known to be NP-complete and therefore a number of heuristic algorithms have been proposed in the literature, we first need to establish which of these are the best candidates for the B-ISDN. We conclude that the weighted greedy -type algorithms are promising ones, and therefore we examine the behavior of these algorithms in terms of blocking probability and network utilization. In doing so, we use a B-ISDN call level simulation program, which proves to be an indispensable tool in the quest for efficient multicast algorithms. We find that shortest path routing with appropriate (adaptive) weight functions combined with the complete partitioning link allocation policy may give satisfactory blocking values and good network utilization in networks of different sizes.