On the capacity of multiwavelength optical-star packet switches

The optical star network and its power budget and spectral-width limits are reviewed. A third capacity limit due to the bandwidth available within the switch for communicating the switch-control functions to the crosspoint elements of the switch is investigated. A pipelined switch processor and the communications bandwidth required within the switch to support the maximum amount of information transfer within that pipelined architecture are considered. Calculation results are presented for two examples, the switching of asynchronous transfer mode (ATM) cells and of data packets of longer duration, and the differing conclusions to which these two cases lead are compared. For short packets. such as in ATM, the power budgets are not a significant factor, and the bandwidth of the control channel is dominant. Increasing that bandwidth by the use of a parallel bus is indicated. For long packets, the power budget is much more important and the control channel less so. In this case, coherent detection adds significantly to the total switch capacity. The impact that these considerations may have on high-speed communications networks is discussed.<>