Scheduling optical packet switches with minimum number of configurations

In order to achieve the minimum traffic delay in a performance guaranteed optical packet switch (OPS) with reconfiguration overhead, the switch fabric has to use the minimum number of configurations (i.e. N configurations where N is the switch size) for traffic scheduling. This requires a very high speedup in the switch fabric to compensate for the loss in scheduling efficiency. The high speedup requirement makes the idea of using N configurations (to schedule the traffic) impractical under current technology. In this paper, we propose a new scheduling algorithm called α i-SCALE to lower the speedup required. Compared with the existing MIN algorithm [5], α i- SCALE succeeds in pushing the speedup bound (i.e. worst-case speedup requirement) to a much lower level. For example, when N=200, the speedup bound required to compensate the loss in scheduling efficiency is 30.75 for MIN, whereas 23.45 is sufficient for our α i-SCALE. © 2005 IEEE.published_or_final_versio

Traffic scheduling in non-blocking optical packet switches with minimum delay

For performance guaranteed OPS switches with reconfiguration overhead, it has been shown that packet delay can be minimized by using N switch configurations (where N is the switch size) to schedule the traffic. However, this usually involves an exorbitant speedup requirement, which makes it impractical under current technology. In this paper, a new minimum-delay scheduling algorithm QLEF (Quasi Largest-Entry-First) is proposed. We prove that QLEF pushes the required speedup bound to the lowest known level. As an example, when N=950, QLEF only requires a speedup of S schedule=21.33 instead of 42.25 for MIN [5] and 30.27 for α i-SCALE [8]. This gives a 50% improvement over MIN and 30% over α i-SCALE. © 2005 IEEE.published_or_final_versio

Feedback-based scheduling for load-balanced two-stage switches

A framework for designing feedback-based scheduling algorithms is proposed for elegantly solving the notorious packet missequencing problem of a load-balanced switch. Unlike existing approaches, we show that the efforts made in load balancing and keeping packets in order can complement each other. Specifically, at each middle-stage port between the two switch fabrics of a load-balanced switch, only a single-packet buffer for each virtual output queueing (VOQ) is required. Although packets belonging to the same flow pass through different middle-stage VOQs, the delays they experience at different middle-stage ports will be identical. This is made possible by properly selecting and coordinating the two sequences of switch configurations to form a joint sequence with both staggered symmetry property and in-order packet delivery property. Based on the staggered symmetry property, an efficient feedback mechanism is designed to allow the right middle-stage port occupancy vector to be delivered to the right input port at the right time. As a result, the performance of load balancing as well as the switch throughput is significantly improved. We further extend this feedback mechanism to support the multicabinet implementation of a load-balanced switch, where the propagation delay between switch linecards and switch fabrics is nonnegligible. As compared to the existing load-balanced switch architectures and scheduling algorithms, our solutions impose a modest requirement on switch hardware, but consistently yield better delay-throughput performance. Last but not least, some extensions and refinements are made to address the scalability, implementation, and fairness issues of our solutions. © 2009 IEEE.published_or_final_versio

Minimizing internal speedup for performance guaranteed optical packet switches

Providing QoS guarantee for Internet services is very important It evokes the issue that packet switches should provide guaranteed performance (i.e. 100% throughput with bounded worst-case delay). Optical switching technology is widely considered as an excellent solution for packet switches in future networks. However, to achieve guaranteed performance in optical packet switches, an internal speedup is required due to the existence of reconfiguration overhead. How to reduce the internal speedup is the main concern for making these switches practical In this paper, we first derive the internal speedup S as a function of the number of switch configurations N S and the reconfiguration overhead δ, or S=f(N S,δ). We show that the recently proposed ADJUST algorithm is flawed. Based on the internal speedup function we derived, a new algorithm (ADAPTIVE), with time complexity of O((λ-l)N 2logN), is proposed to minimize S. © 2004 IEEE.published_or_final_versio