Cost-effective WDM broadcast-and-select networks for all-to-all transmission schedules

In WDM broadcast-and-select networks, either the transmitters or receivers must be tunable to ensure complete network connectivity. However, the lasers and filters fabricated by the current device technology require a significant tuning time compared with the packet transmission time. To hide the tuning time, a previous study proposed to use multiple tunable transmitters per input and multiple receivers per output to pipeline transmission/reception with tuning. In this paper, we study an alternative and cheaper network configuration to hide the tuning time for all-to-all transmission scheduling (i.e., scheduling a packet transmission between every input-output pair). In this configuration, every electronic transmitter (receiver) is connected to l tunable lasers (f fixed-tuned filters), so that we can pipeline transmission/reception with tuning. We show that our network configuration can give nearly the same schedule length as the network studied in previously published results at a significantly lower cost. Therefore, our network configuration is more cost-effective to hide the tuning time. In addition, we derive lower bounds on optimal schedule lengths and show that they are tighter than those derived in previously published results.