Traffic scheduling in a photonic packet switching system with QoS guarantee

The main challenge in the design of future broadband networks is to efficiently support high-bandwidth multimedia services. Recent advances in the optical networking reveal that all optical networks offering multigigabit rate per wavelength may soon become economical as the underlying backbone in wide area networks, in which photonic switch plays a central role. Two issues are the essential in the design of photonic packet switching, the support of end-to-end virtual connections and the support of diverse quality-of-service (QoS) services. Existing work in wide-area optical networks has largely focused on the former, relatively less attention has been given to support heterogeneous traffic types and to satisfy the potentially different QoS requirements of different types of traffic. In this paper, we introduce a novel hierarchical scheduling framework to use in a class of photonic packet switching systems based on WDM, in which we separate the flow scheduling from the transmission scheduling. We show such separation is essential for achieving scalability such that large input-output ports can be accommodated, and also for offering flexibility in that optimal scheduling algorithms can be derived in different level that can be best tuned to the specific system requirements. The salient feature of the proposed scheduling mechanism is that it takes into account potentially different QoS requirements from different traffic flows. A number of interesting findings are observed from the results obtained by both analysis and simulation: (1) QoS requirements can be satisfied for both real-time and nonreal-time flows; (2) the impact Of the real-time traffic head-of-line (HoL) blocking on the system throughput can be effectively alleviated with the prevailing number of traffic flows. In addition, we investigate a variety of performance measures under different system configurations.