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Quality-of-service (QoS) provisioning is an essential feature in next-generation networks. In this paper, we investigate the ability of optical burst switching (OBS) networks to guarantee loss-free transmission inside the network for guaranteed bursts. More specifically, we propose a QoS approach, called path-based QoS provisioning (PQP), to provide absolute QoS provisioning for OBS networks. PQP relies on: 1) routing and wavelength assignment to establish, whenever possible, nonoverlapping paths between each pair of OBS edge nodes and 2) a synchronization scheme to guarantee QoS when the solution in 1) contains overlapping paths because of the limited number of wavelengths. For 1), we propose a routing and wavelength assignment approach, which uses an efficient integer linear programming (ILP) model to determine routing paths and a tabu search algorithm to assign wavelengths to these paths. For 2), we propose a path synchronization scheme, called path-based synchronous transmission scheme (PST). PST synchronizes the transmissions in each set of overlapping paths while maximizing the capacity of each path to transmit guaranteed traffic and guaranteeing fairness when allocating bandwidth to conflicting paths; this is performed using efficient ILP formulations. To improve the performance of best effort traffic and preserve statistical multiplexing gain and high resource utilization of the OBS network, we propose a wavelength selection scheme, called path-based best effort wavelength selection scheme, to send best effort bursts. Simulation results using ns-2 simulator show that PQP successfully provides absolute QoS provisioning for guaranteed traffic and improves significantly the performance of best effort traffic.