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.
To cater for the burst characteristic of IP traffic, WDM networks are expected to reconfigure the virtual topologies corresponding to the real-time changes of the traffic flow. This paper introduces the elementary algorithms of the virtual topology reconfiguration. Compared to each other, we point out their advantages and disadvantages. Then our paper focuses on the tradeoff between the benefits and costs brought by the reconfiguration of the virtual topologies. We present a evaluation function and two thresholds, namely a lower and a higher. Our presented approach balances between the benefits and costs due to the reconfiguration of the virtual topology, increasing the benefits as much as possible while guaranteeing the low costs, with a distinguished characteristic of taking the state of the network into consideration.
As a new solution of all optical networks, Optical burst switching (OBS) has been wildly studied in recently years for its high traffic throughput and high resource utilization at current technology level. In this paper we address some issues of efficient contention resolution: burst segmentation and deflection routing. Under the Just-Enough-Time (JET) protocol based OBS networks architecture, control packet is the guider for corresponding data burst during the transmission. Taking these into consideration, here we propose a novel segmentation strategy - current burst segmentation (CBS) and a modified deflection routing strategy fit for JET based OBSN. Through analysis and simulation, it is shown that these new strategies perform well.
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.
A novel multistage optical cross-connect (OXC) that combined the advantages of three technologies of Space Division Switching (SDS), Wavelength Division Switching (WDS), and Optical Time-Division Multiplexing (OTDM) has been proposed. The structures of the first and second stages of a 2 X 2 and a 4 X 4 OXC have been presented. By means of the splitter and delivery (SAD) switch, it is cost-effective and fully modularized and very convenient to scale to n X n OXCs suitable for large-scale backbones.