Scheduling in data center networks with optical traffic grooming

An optically groomed data center network (OGDCN) is a hybrid optical data center network that uses optical combiners, optical wavelength routers and packet switching components. In this architecture, each compute and storage node (CSN) is equipped with one or more tunable optical transceivers. Communications is enabled by having a sender and receiver tune to the same wavelength at the same time. Multiple transmitters using shared link segments when tuned to the same wavelength at the same time will result in collisions. Scheduling is required to prevent collisions across the network and to allot time slots to satisfy packet demands and coordination. We show that this scheduling problem is NP-complete and present two heuristics to solve this problem in a centralized server. The first heuristic (CTEF) assumes continuous time and computes the earliest free time duration for communication. The second heuristic (SLIT) uses slotted time and intersecting time within the allotted time slot for communication. The network utilization achieved by these heuristics is analyzed. It is shown that the CTEF and SLIT heuristics attain 99% and 98% utilization respectively.