Statistical multiplexing in optical flow switching networks

Abstract

In IP over WDM networks, optical paths (OP's) form a virtual topology seen from the upper IP layer, and greatly relieve the burden of electronic processing thanks to optical bypasses. However, in contrast to the circuit-switching, connection-oriented and coarser OP's, the IP is packet-switching, connectionless and finely granular in nature. Special care should be taken in the control plane to bridge the gap. In our research, we incorporate the idea of optical flow. Optical flows are optically switched in intermediate nodes and converted into electronic form at termination to treat small nested flows. Two modes of optical flow switching (OFS) are examined. One is optical burst switching (OBS), which sends control packet ahead of data to announce a switching and make future reservations. The other is Optical Grooming Switching (OGS), which put packet flows into finer container with discrete yet flexible bit rate. We find that both of these two modes use statistical multiplexing to bridge the gap between IP packets and WDM OP's, and such function is fulfilled respectively by scheduling in OBS and by framing in OGS. Taking snapshots of statistical multiplexing, we formulate the bandwidth distribution (BWD) of the whole OFS networks and the bandwidth usage (BWU) over each node pair. The BWD can be expressed by the product of a traffic-independent grooming matrix with the traffic demand matrix under a given virtual topology. Changes to the grooming matrix are reflected by adjustments in framing or scheduling. Three distinct states of BWU are also identified to determine the initiation of such changes. The BWU states are hence proposed to add to the extension of existing routing protocols.