On the Performance of Dynamic Online QoS Routing Schemes ⋆ Antonio Capone, Luigi Fratta, and Fabio Martignon DEI, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milan, Italy {capone,fratta,martignon}@elet.polimi.it Abstract. Several dynamic QoS routing techniques have been recently proposed for new IP networks based on label forwarding. However, no extensive performance evaluation and comparison is available in the lit- erature. In this paper, after a short review of the major dynamic QoS routing schemes, we analyze and compare their performance referring to several networks scenarios. In order to set an absolute evaluation of the performance quality we have obtained the ideal performance of any routing scheme using a novel and flexible mathematical programming model that assumes the knowledge of arrival times and duration of the connections offered to the network. This model is based on an extension of the maximum multi-commodity flow problem. Being an integer linear programming model, its complexity is quite high and its evaluation is constrained to networks of limited size. To overcome the computational complexity we have defined an approximate model, based on the multi- class Erlang formula and the minimum multi-commodity cut problem, that provides an upper bound to the routing scheme performance. The performance presented in the paper has been obtained by simulation. From the comparison of the schemes considered it turns out that the Virtual Flow Deviation routing algorithm performs best and it almost reaches, in several scenarios, the ideal performance showing that no much gain is left for alternate new schemes. 1 Introduction The current evolution of Internet architecture is towards service differentiation and Quality of Services (QoS) support [1]. In order to offer guaranteed end-to-end performance (as bounded delay, jitter or loss rate), it is necessary to introduce some sort of resource reservation mechanism and traffic control. With classical IP routing, however, when the resources are not available on the shortest path, the connection request is rejected even if sufficient resources exist on alternative paths. With new label based forwarding mechanisms, such as MPLS (Multi Proto- col Label Switching) [2] and GMPLS (Generalized MPLS) [3, 4], per flow path selection is possible and QoS parameters can be taken into account by routing al- gorithms. The goal of QoS routing schemes is to select a path for each traffic flow ⋆ This work has been partially supported under the grant of MURST Tango project. M. Ajmone Marsan et al. (Eds.): QoS-IP 2005, LNCS 3375, pp. 456–469, 2005. c  Springer-Verlag Berlin Heidelberg 2005