An optical switching architecture for hierarchical group communication

We show that the problem of finding the maximum passable subset of a permutation through a banyan is NP-complete. We then describe a two-level optical interconnection structure for groups or clusters of end-nodes (LANs or processors). At the higher level, an optical banyan is used to switch wavelength multiplexed packets from the groups. Technologically difficult switching of individual wavelengths is avoided by prearranging transmissions from the groups in a way that they can be switched in a wavelength insensitive manner. Further, by keeping the banyan conflict free, we allow each of the groups to access the entire set of wavelengths for multiplexing, thus maximizing the bisection bandwidth. The proposed optical interconnect can support multiple multicast connections between each pair of groups, in which source nodes may simultaneously multicast several different packets to different subsets within a destination group. System-wide multicasts and broadcasts can be achieved through repetitive group-to-group transmissions. The network uses readily available components such as opto-electronic directional couplers, fixed wavelength transmitters, and diffraction-based parallel receivers while avoiding the use of relatively slow and expensive tunable components.