Scheduling variable-size packets in the DAVID metropolitan area network

DAVID is a research project sponsored by the European Union aimed at the design of an optical packet-switched network for the transport of IP traffic. The DAVID network has a two-level hierarchical structure, with a backbone of optical packet routers interconnected in a mesh, and metropolitan areas served by sets of optical rings interconnected by passive memoryless devices called Hubs. The paper focuses on the metropolitan area network and its components: the nodes and the Huh. Access is regulated by a dynamic time-division multiple-access scheme allocating slots in sets of wavelengths that provide multichannel pipes among ring pairs. This paper proposes a new resource allocation scheme capable of transporting variable-size packets without segmentation into fixed-size data units. Resource sharing among nodes is granted by two scheduling algorithms running on different time scales: the first one is centralized at the Hub and provides coarse connectivity among ring pairs; the second one runs at nodes and provides finer node-to-node connectivity. The Hub scheduling algorithm is derived from well known algorithms in the literature; a novel heuristic scheduling algorithm running at nodes is proposed for datagram (not-guaranteed) traffic and its performance is studied by simulation.