Zhizhong Zhang

The impacts of burst assembly on the traffic properties in optical burst switching networks

Optical burst switching (OBS) is regarded as one of the most promising solutions for the next generation backbone. Burst assembly in the edge nodes is an important issue to be addressed in OBS networks. In this paper, the impacts of burst assembly using different schemes on the Poisson traffic properties are investigated and simulated. The results are shown that the intervals of assembled burst arrivals are short dominant, but their service time distributions are much different from each other due to different assembly schemes. When the timer-based scheme is used, a normal-like distribution is obtained, while a long dominant one is obtained when threshold-based scheme is adopted. In addition, the product of the traffic load and time rate keeps invariable in both cases.

A new burst assembly and dropping scheme for service differentiation in optical burst switched networks

It has been proved that through burst segmenting, and thus dropping the segment of one burst that is overlapped with another burst, the packet loss probability will be significantly improved for optical burst switched networks. Based upon this, two main segment dropping strategies, head- and tail-dropping, can be used to resolve contention. In this paper, we point out that tail-dropping policy, which is adopted in most literatures, may not be a feasible solution, while head-dropping policy, even though it may make the packets to arrive out of order, is in deed a solution which can resolve the contention effectively. Moreover, with respect to tail-dropping policy, the increase of the disorder of packet arrivals for head-dropping policy is trivial. To support service differentiation and decrease the disorder of packet arrivals generated by contention resolution, we further propose a new threshold-based hybrid-assembly scheme. The most striking characteristic of the hybrid-assembly scheme is that the low and high packet classes are aggregated into one burst simultaneously. Once contention occurs, head-dropping policy is adopted to drop the overlapping packets. We describe the concrete implementation of QoS supporting, and the corresponding dropping strategy -- improved head-dropping policy, which aims at guaranteeing a better QoS support and a feasible implementation, is also detailed. Simulation results demonstrate that the proposed burst assembly scheme, together with the head-dropping policy, perform well in terms of performance metrics such as the average packet loss probability and service differentiation.

A new topology discovery protocol for multi-ring interconnected resilient packet rings

Resilient Packet Ring (RPR) is an emerging network architecture and technology designed to meet the requirements of packet-based metropolitan area network (MAN). IEEE 802.17 RPR Draft Standard[1] defines RPR dual-ring topology discovery protocol. In this paper, we propose a new RPR multi-ring interconnected network. RPR multi-ring interconnected network has better resource availability and better bandwidth utilization than RPR dual-ring topology. So how to extend RPR dual-ring topology to RPR multi-ring interconnected network really deserves our attention. RPR multi-ring network is formed by decreasing the scale of standard RPR and interconnecting several small scale standard RPR rings together through cross-stations. The new topology discovery algorithm uses the method of multi-layer subnet topology discovery in clockwise implemented by the multi-ring automatic topology discovery module in cross-station’s MAC control layer. Furthermore, we bring forward the unit structure of tree-like bi-direction list and of topology information list. The paper mainly contains the two parts: RPR standard topology discovery algorithm and RPR multi-ring interconnected topology discovery algorithm.

Novel threshold-based burst assembly scheme for QoS support in optical burst switched WDM networks

In this paper, we propose a new threshold-based mixed-assembly technique with QoS support in optical burst switched networks. The most striking characteristic of the mixed-assembly policy is that both the low and high packet classes are aggregated into one burst simultaneously. Once contention occurs, there will be an overlap between the tail of the earlier arriving burst and the head of the contending burst. Combing with burst segmentation technique, we drop the tail of the earlier arriving burst that is mainly made up of low priority packets, thus the packet loss probability of the high packet classes will be guaranteed. Simulation results show that the proposed burst assembly scheme performs well in terms of performance metrics such as the average packet loss probability and the packet loss probability of the high class of traffic.

On the design and performance study of 2-to-1 switching node for all-optical packet switching

This paper investigates the implementing techniques concerning 2-to-1 node receiver for all-optical packet switching. We point out that the state-of-the-art technologies introduced in the literatures are all associated with one main limitation, i.e., even if two incoming packets are directed to the different ports and thus no contention will occur, they can not be directed to the output ports simultaneously. To overcome this problem, a novel node receiver model is proposed in this paper. This work presents a solution that makes use of fiber delay-lines (FDLs) which allow multiple packets to be concurrently stored or transmitted. With a novel switch control, it is shown that this solution is very efficient to resolve contention, and overcomes the limitation existing in the current models (e.g., Quadro, M-Quadro and COD architectures). We describe and analyze the concrete scheduling of the switches. Simulation results based on bursty and non-bursty traffic scenarios demonstrate that the proposed node architecture (1) performs well in terms of performance metrics such as packet loss probability; (2) has a simple control requirement. In addition, we find that the required number of the recirculating time of the packets is minimal.

Control and scheduling strategies for the recirculation shared-memory optical buffer in optical packet switched network

This paper focuses on the problem of optical buffer control strategies for recirculation shared optical buffer in optical packet switching. Five control algorithms are presented, and their performances are evaluated and compared by computer simulations. Issues on the optimal configuration of optical buffers are also discussed. The numerical results show that the time delay resolution of fiber delay line has significant influence on the system performance in all three discussed switching mode. The results are valuable in designing the optical packet switch.

QoS performance of fixed-length optical burst switching

In this paper, inefficiencies of the QoS scheme based on extra-offset-time-based priority for variable-length optical burst-switched network were pointed out, and a novel fixed-length burst assembly scheme is proposed. This scheme is not only practical, but also able to decrease the latency of bursts at the edge nodes. Compared to variable-length (traditional) scheme, a smaller blocking probability for the highest priority service and almost one third offset time delay for every class were obtained in fixed-length scheme.

Fairness of QoS supporting in optical burst switching

In this paper we investigate the fairness problem of offset-time-based quality of service (QoS) scheme proposed by Qiao and Dixit in optical burst switching (OBS) networks. In the proposed schemes, QoS relies on the fact that the requests for reservation further into the future, but for practical, benchmark offset-time of data bursts at the intermediate nodes is not equal to each other. Here, a new offset-time-based QoS scheme is introduced, where data bursts are classified according to their offset-time and isolated in the wavelength domain or time domain to achieve the parallel reservation. Through simulation, it is found that this scheme achieves fairness among data bursts with different priority.

Controllable Bandwidth Allocation in Optical Burst-Switched Networks†

A novel, simple and controllable bandwidth allocation scheme, called bandwidth on Demand (BoD), is proposed for optical burst-switched network in this paper. It assures every service class to consume bandwidth no more than its granted percentage by examining the bandwidth usage of each class periodically. The burst loss ratios under arbitrary input loads are theoretically analyzed as well as numerically simulated. The theoretical descriptions accord with the simulated results very well. The scheme can be used as an effective scheme of bandwidth allocation and management.

A new 2/spl times/1 node receiver architecture for packet switched networks

This paper proposes a new 2/spl times/1 node receiver architecture for all-optical packet switched networks, whose basic principle can be extended to construct a larger buffer if more 2/spl times/2 switches and fiber delay lines (FDLs) are available. The most striking characteristic of the architecture is that the buffer is achieved by a combined use of feed-forward and feedback FDLs. We describe and analyze the concrete two-stage FDL architecture as it has the advantages of being the cheapest and simplest multi-stage solution. As for control strategy, we demonstrate that bottom control strategy (BCS), which use FDL that is arranged in the feed-forward form when both feed-forward and feedback FDLs are available, is a more robust solution against bursty traffic. Simulation results show that the developed architecture (D.K. Hunter, W.D. Cornwell et al., October 1998) performs well in terms of performance metrics such as packet loss probability; (Z. Haas, 1993) has a simpler control requirement and a better packet loss probability than M-quadro [I. Chlamtac et al., December 2000].