Comparative study of QoS mechanisms in OBS networks M. Klinkowski 1,2 , D. Careglio 1 , M. Marciniak 2 and J. Solé-Pareta 1 1 Advanced Broadband Communication Centre, Universitat Politècnica de Catalunya, Jordi Girona 1-3, 08034 Barcelona, Spain Tel: +34 93 4017182, Fax: +34 93 4017055, E-mail: {mklinkow, careglio, pareta}@ac.upc.edu, 2 Department of Transmission and Fibre Technology, National Institute of Telecommunications, 1 Szachowa Street, 04-894 Warsaw, Poland Tel: +48 225128715, Fax: +48 225128347, E-mail: M.Marciniak@itl.waw.p In this paper, we address the problem of Quality of Service (QoS) provisioning in Optical Burst Switching (OBS) networks. When examining the literature on OBS we can find several proposals of mechanisms dealing with QoS. As these mechanisms are evaluated in a specific node/network scenario each one, the results are usually not comparable. The aim of this work is to confront the performance of the most referenced QoS mechanisms in the same evaluation scenario consisting of a single isolated node. 1. Introduction OBS is one of the potential solutions with more future in the optical networking panorama [1]. On the one hand, it efficiently exploits statistical multiplexing in the optical layer to overcome the wavelength switching inefficiency. On the other hand, it uses large data bursts to overcome the fast processing and switching requirements of the optical packet switching (OPS) currently only available at the laboratory. On the contrary to the OPS, the client packets are aggregated and assembled into bursts at the edge nodes of OBS network. Meanwhile, the control information is transmitted out-of-band by a control packet (CP) and sent with some offset prior to the burst in order to reserve resources (like wavelengths) on the transmission path for the incoming burst. There are two distinct signaling architectures considered for OBS networks. The first one performs end-to-end resources reservation with acknowledgment in so called two-way reservation mode (WR-OBS) [2] while the other allocates resources on-the-fly a while before burst coming in a one-way reservation [1]. The problem of WR-OBS networks concerns the latency due to the connection establishment process [3], [4], therefore such architectures are considered mainly for the lower distance metro networks. The one-way reservation model that can operate in large distance OBS networks performs according to the statistical multiplexing paradigm; hence it encounters the problem of burst contention inside the network. Indeed, when CP enters a node in order to make a reservation of an output fiber and wavelength for the associated