Master Thesis - 2008

Recently, all optical Wavelength Division Multiplexing networks are developed as the network realizing high-speed and large capacity. In particular, Optical Packet Switching network is promising candidate for next generation network architecture because it has high compatibility for traditional IP networks. It is difficult for optical level switches to resolve contention by simple buffering like IP routers. Programmable variable delay lines, which have several lengths of FDLs (Fiber Delay Line), have been developed as collision avoidance devices. It can delay packets in variable durations by various FDLs.

Two-stage switch with this programmable variable delay lines has been proposed as one of the optical switches. Two-stage switch can foresee following packets and schedules packets with the programmable variable delay lines (called Look-ahead Buffer). By this look-ahead scheduling, two-stage switch can avoid contentions effectively in time domain. Meanwhile, two-stage switch has FDLs, which re-input a packet from the output to the input (called Loop-back Buffer), and the Loop-back Buffer also can avoid contentions. However, existing studies only focus on the scheduling of the Look-ahead Buffer and intelligent usage of the Loop-back Buffer is actually out of concern.

In this thesis, a packet transfer scheduling method that uses two buffers is proposed. The proposed method controls both the Look-ahead Buffer and the Loop-back Buffer cooperatively and improves the utilization of the switch. The effectiveness of the proposed method is evaluated through simulation experiments. As a result, the proposed method can reduce the packet loss probability effectively. In particular, the proposed method reduces the packet loss probability down to nearly zero when the traffic load is light. Finally, the processing speed of the proposed scheduling method is evaluated and the feasibility of the proposed method is confirmed.