This paper proposes three-domain (3-D) burst scheduling in optically burst-switched WDM networks. This scheme completely eliminates contention at intermediate core nodes by combining contention avoidance schemes in the space, wavelength, and time domains. In the space and wavelength domains, the proposed scheme constructs multiple fixed, tree-shaped routes for burst transmission called λ-trees, each of which is assigned a wavelength. Note that λ-trees with the same wavelength do not share any links, and therefore the proposed scheme provides contention-free transmission among bursts transmitted on different λ-trees. Furthermore, in the time domain, the proposed scheme introduces an ingenious offset time assignment scheme named burst grooming, which eliminates contention on each λ-tree. As a result, contention at intermediate core nodes is completely eliminated because each ingress node schedules incoming bursts onto λ-trees with burst grooming. We provide λ-tree construction and burst scheduling algorithms, which aim to minimize the overall burst loss probability. Extensive simulation experiments show that the proposed scheme improves the overall burst loss performance dramatically without wavelength conversion.
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