A hybrid buffer structured optical packet switch and its scheduling algorithm are presented for a limited number of tunable wavelength convertors (TWCs) and internal wavelengths. The hybrid buffer consists of the fiber delay line (FDL) buffer and the electronic buffer. With the proposed algorithm, it could lead realizable packet loss reduction that the LAUC-VF algorithm with only the FDL buffer does not reach. Also, we optimized the number of TWCs and internal wavelengths of the hybrid buffer structured OPS. For the fully shared TWC structure, the optimum number of TWCs and internal wavelengths to guarantee minimum packet loss is evaluated to prevent resource waste under the hybrid buffer.

An important issue in the realization of optical packet-switched (OPS) networks is the resolution of packet contention caused by the lack of RAM-like optical buffering. Although an optical buffer using fiber delay lines (FDLs) has been proposed, its capacity is extremely limited. There have been several studies of this problem. One approach is deflection routing, which is widely used in electronic packet-switched networks or optical burst-switched (OBS) networks. However, in OPS networks, packet lengths are short, so that the speed requirement for route lookup is very stringent. If the network topology is geometric, such as a Manhattan Street Network (MSN), hop-by-hop routing can be implemented by simple optical logic devices without an electronic routing table. However, if the topology is not geometric, it is hard to implement deflection routing electronically or optically. Another approach is reflection routing, which is easy to implement but has a higher probability of packet loss than does deflection routing. In this paper, we propose a packet contention resolution scheme, reflection-based deflection routing, which is based on reflection routing and enables switching the reflected packet to an alternate path if its primary path remains congested. Our method alleviates the time limitation on setting an alternate path by making use of the packet reflection latency and also reduces the probability of packet loss. We evaluate the performance of the proposed method by simulation experiments and show its effectiveness.

In an effort to reduce switch cost, we present the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths required for contention resolution of asynchronous and variable length packets, in the optical packet switch (OPS) with the shared fiber delay line (FDL) buffer. To optimize TWCs and internal wavelengths related to OPS design cost, we proposed a scheduling algorithm for the limited TWCs and internal wavelengths. For three TWC alternatives (not shared, partially shared, and fully shared cases), the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of an OPS with full TWCs and internal wavelengths.

This paper compares selected Optical Packet Switching architectures that use the wavelength conversion technique to solve the packet contention problem. The architectures in question share wavelength converters, which are needed to wavelength translate arriving packets. This paper focuses on two architectures: the Shared Per Output Line (SPOL) and the Shared Per Input Line (SPIL) architectures, in which the wavelength converters are shared per output and input fiber respectively. The performance of the proposed architectures is evaluated for all the balance/unbalance combinations of input/output traffic. Packet loss probability is expressed as a function of the number of wavelength converters used, by means of analytical models validated by simulations. The results obtained show that the SPIL architecture, when compared to the SPOL architecture, allows for greater economies in terms of number of wavelength converters needed. While the performance of the two architectures tends to have similar values in a scenario with unbalanced input traffic and balanced output traffic, in unbalanced output traffic scenarios the SPIL architecture requires about 50% less wavelength converters than the SPOL architecture does, for a given packet loss probability.

In the future network, optical technology will play a stronger role not only for transmission but also for switching. Optical burst switching (OBS) emerged as a promising switching paradigm. It brings together the complementary strengths of optics and electronics. This paper presents the design and implementation of an overlay mode burst-switched photonic network testbed, including its architecture, protocols, algorithms and experiments. We propose a flexible "transceiver + forwarding" OBS node architecture to perform both electronic burst assembly/disassembly and optical burst forwarding. It has been designed to provide class of service (CoS), wavelength selection for local bursts, and transparency to cut-through bursts. The functional modules of OBS control plane and its key design issues are presented, including signaling, routing, and a novel scheduling mechanism with combined contention resolution in space and wavelength domains. Finally, we report the experimental results on functional verification, performance analysis and service demonstration.

The ranging algorithm allows active stations to measure their distances to the headend for synchronization purpose in Hybrid Fiber Coax (HFC) networks. A practicable mechanism to resolve contention among numerous stations is to randomly delay the transmission of their control messages. Since shorter contention cycle time increases slot throughput, this study develops three mechanisms, fixed random delay, variable random delay, and optimal random delay, to minimize the contention cycle time. Simulation demonstrates that the optimal random delay effectively minimizes the contention cycle time and approaches the theoretical optimum throughput of 0.18 from pure ALOHA. Furthermore, over-estimation reduces the impact on contention cycle time more than under-estimation through sensitivity analysis, and both phenomenon damage slot throughput. Two estimation schemes, maximum likelihood and average likelihood, are thereby presented to estimate the number of active stations for each contention resolution round. Simulation proofs that the proposed estimation schemes are effective even when the estimated number of active stations in initial contention round is inaccurate.