Optimisation of optical burst switched networks using multi-objective BAT algorithm

The most important design goal in Optical Burst Switching (OBS) networks is to reduce burst loss resulting from resource contention. Especially, the higher the congestion degree in the network is, the higher the burst loss rate becomes. The burst loss performance can be improved by employing an appropriate congestion control. In this paper, to actively avoid contentions, we propose a dynamic load-aware congestion control scheme that operates based on the highest (called ‘peak load’) of the loads of all links over the path between each pair of ingress and egress nodes in an OBS network. We also propose an algorithm that dynamically determines a load threshold for adjusting burst sending rate, according to the traffic load in a network. Further, a simple signalling method is developed for our proposed congestion control scheme. The proposed scheme aims to (1) reduce the burst loss rate in OBS networks and (2) maintain reasonable throughput and fairness. Simulation results show that the proposed scheme reduces the burst loss rate significantly, compared to existing OBS protocols (with and without congestion control), while maintaining reasonable throughput and fairness. Simulation results also show that our scheme keeps signalling overhead due to congestion control at a low level.

Since Transmission Control Protocol (TCP) is the dominant protocol on the Internet and optical burst switching (OBS) networks represent the optical transmission solution that can meet future high bandwidth requirements, TCP and OBS networks represent a possible combination for the next-generation Internet. However, a problem with this combination model is that operations at the OBS layer need to be controlled so that false congestion detection at the TCP layer is minimised. Considering the combination of TCP Vegas and OBS, congestion detection at the TCP layer is based on the round-trip time (RTT), where congestion is detected if the current RTT exceeds a given RTTmax. The extra delay may be due to some actual loss, but it may also be due to the extended execution time caused by some OBS layer operations. Therefore, reducing the time of operations at the OBS layer will reduce false congestion detection at the TCP layer. This paper investigates the impact of reducing the buffering time at the ingress node on the false congestion detection rate at the TCP layer. The reduction of the burst buffering time is accomplished by nesting the offset time in the assembly time. The simulation results and analysis show that the transmission efficiency in TCP Vegas over OBS networks is significantly improved; the throughput remains high, and the delivery success rate is significantly increased compared to the conventional buffering mode.

A crucial issue in optical burst switching (OBS) networks is burst loss caused by resource contention. As a result, many methods are currently being proposed to reduce burst loss rate. These methods can be summed up into two categories: burst scheduling algorithms and contention resolutions. Both categories of methods can reduce burst loss rate to a certain degree. However, to make OBS to become a viable solution, the burst loss rate needs to be further reduced. Furthermore, almost all methods ignore the fact that an unfortunately scheduled, locally generated single-hop burst could block a number of future incoming transit bursts, though the burst just travels to its next downstream node. This phenomenon becomes more evident when links are heavily loaded in mesh OBS networks. To eliminate contention caused by single-hop traffic completely, this paper proposes a novel transfer mode called packet calking by differentiating between single-hop traffic from multihop traffic for OBS networks. An analysis model is developed to evaluate the performance of packet calking. Theoretical results are validated through extensive simulations in both ring and mesh networks. These results show that packet calking outperforms the transfer mode without packet calking in terms of burst loss rate and link utilization.

Data burst contentions occur in optical burst-switched (OBS) networks due to one-way signaling and bufferless nature of the core network. A single burst loss containing multiple TCP segments can trigger drastic reactions from the corresponding TCP sources. TCP sender interprets segment loss as network congestion, resulting in throttling send rate. In this paper, we propose a new forward segment redundancy (FSR) mechanism that minimizes segment loss during burst contentions in the core and also recovers from segment loss in the forward direction using redundant segments placed in each data burst. In FSR mechanism, redundant TCP segments are added to each burst assembled at the ingress node before transmission to the destination. The segment losses due to contentions are minimized using a modified burst segmentation mechanism, and most lost segments are recovered in the forward direction using redundant segments. Using FSR, we observe significant improvement in TCP performance over OBS networks.

In order to achieve service differentiation, especially loss differentiation, in optical burst switching (OBS) networks, we propose a dynamic fiber delay line (FDL) partitioning algorithm, which divides FDLs into several groups over a feed-forward output buffering architecture. In the proposed scheme, a plurality of traffic classes and FDL groups can be considered, and each FDL group is assigned to traffic classes, so that the target loss probabilities of classes are guaranteed. Also, the optimal number of FDLs for each FDL group by the proposed algorithm is decided in Poisson traffic environments. The extensive simulation results validate the effectiveness of the proposed dynamic FDL partitioning algorithm for the loss differentiation in OBS networks.

In optical burst switching (OBS) networks, when contention occurs at an intermediate node, two or more bursts that are in contention can be dropped because a forwarding path reservation is not made for a burst. This is the reason why one of the critical design issues in OBS networks is finding ways to minimize burst dropping resulting from resource contention. In this paper, we propose a configuration management policy based on an operation cost model developed according to network status information which relates to guaranteeing quality of service (QoS). Also, we develop the criteria for the configuration management by providing the alternate path using bounded range of the sensitivity of this cost model. Finally, throughout the theoretical and experimental analysis, we can obtain that our proposed scheme has good performance in an aspect of blocking rate and outperforms the conventional scheme in complexity as results

In optical burst switching (OBS) networks, the contention of optical bursts is the most serious problem due to the lack of buffers within the networks. Various deflection routing schemes and a routing scheme based on pre-calculated multiple paths have been proposed to resolve the contention. The latter routing scheme can successfully maintain a relatively limited transfer delay of optical bursts. This paper proposes a new decentralized routing scheme based on multiple paths to effectively resolve the contention of optical bursts. In this scheme, each source node splits the traffic load into pre-calculated multiple paths adaptively according to the measured loss rate of the optical bursts transferred through each path. This scheme does not require frequent notification of the measured loss rate because each source node selects one of the multiple paths probabilistically. In the OBS networks, the average transfer delay in the multi-path routing always exceeds that in a single-path routing because alternative paths with a larger transfer delay are also utilized in the multi-path routing. Thus, this paper proposes an adaptive load splitting method in which load splitting ratios for the multiple paths are autonomously adjusted to minimize the average transfer delay based on the condition that the required loss rate of optical bursts is satisfied. The performance of the proposed scheme was evaluated by computer simulation and based on the evaluation results; the ability of the proposed scheme to adjust the load splitting ratios for the multiple paths autonomously and avoid the contention of optical bursts adaptively is clarified even if the traffic load applied to the OBS network changes.

The burst contention has a strong impact on the performance of optical burst switching (OBS) network, and currently, various contention resolution schemes have been proposed from time domain, space domain and wavelength domain, respectively. Among the schemes, the deflection routing is more attractive, which can loosen the requirement of optical buffer in capability and quantity. With deflection routing, the contending burst is rerouted to an available port other than the intended output instead of being dropped. However, when the traffic load is high, there should not be only more contentions but also frequent deflection routings, some of which might aggravate the network status. To improve the status, this paper proposes the tunable-parameter deflection routing (TPDR) algorithm, which can control the deflecting operation of a contending burst by a tunable-parameter, i.e., deflection probability, which is settled by the priority and traffic load of contending burst, and search the optimum deflection path in terms of the burst loss probability and the path length. The simulation results show that it can improve the overall BLP and the BLP of each individual priority, and alleviate the negative effect of the offset-time deficit on QoS guarantee.

Enhanced packet routing queuing model in optical burst switching network using queue-based dynamic optical route scheduling

This paper studies the blocking performance of optical burst switching (OBS) networks using a sequential office control (SOC) state-independent deflection routing policy. We show that unprotected deflection routing may destabilize OBS resulting in higher blocking probabilities than if bursts were not deflected but simply blocked. This study was motivated by the well-known destabilizing effect that alternative routing has on circuit switching in classical telephony networks. We propose two forms of protection to guard against destabilization: 1) wavelength reservation, which is analogous to trunk reservation in circuit switching; and, 2) preemptive priority, which is a new form of protection where bursts that have not been deflected are given preemptive priority over bursts that have been deflected. Our main contribution is a one-moment reduced-load approximation to evaluate the blocking performance of OBS networks using deflection routing protected by either wavelength reservation or preemptive priority. Our reduced-load approximation relies on the usual assumptions of link independence and Poisson distributed link arrivals. We quantify the error admitted in making these two assumptions via simulation. Using our reduced-load approximation, we evaluate the blocking performance of protected and unprotected deflection routing in several randomly generated networks. The chief conclusion of our study is that deflection routing in OBS should be given some form of protection to avoid destabilization resulting from upward load variations, and in terms of blocking performance, preemptive priority is the best form of protection for OBS. We use simulation to verify that our conclusions remain valid for a realistic traffic scenario.

Next-generation high-speed Internet backbone networks will be required to support a broad range of emerging applications which may not only require significant bandwidth, but may also have strict quality of service (QoS) requirements. Furthermore, the traffic from such applications are expected to be highly bursty in nature. For such traffic, the allocation of static fixed-bandwidth circuits may lead to the over-provisioning of bandwidth resources in order to meet QoS requirements. Optical burst switching (OBS) is a promising new technique which attempts to address the problem of efficiently allocating resources for bursty traffic. In OBS, incoming data is assembled into bursts at the edges of the network, and when the burst is ready to be sent, resources in the network are reserved only for the duration of the burst. The reservation of resources is typically made by an out-of-band one-way control message which precedes the burst by some offset time. By reserving resources only for the duration of the burst, a greater degree of utilization may be achieved in the network. This book provides an overview of optical burst switching. Design and research issues involved in the development of OBS networks are discussed, and approaches to providing QoS in OBS networks are presented. Topics include: - Optical burst switching node and network architectures - Burst assembly - Signaling protocols - Contention resolution - Burst scheduling - Quality of service in OBS networks

In this paper, we investigate the problem of multipath traffic engineering in optical burst switching (OBS) networks. The main goal of this work is to minimize burst loss rate in the network by adaptively balancing the burst traffic among multiple paths based on the measurement and analysis of path congestion. We develop three distributed traffic splitting algorithms by considering the special features of OBS networks. Among these three algorithms, one algorithm considers burst level traffic distribution, and the other two algorithms consider flow level traffic distribution to avoid packet reordering problem. The proposed multipath traffic engineering algorithms achieve significant performance improvement in reducing burst loss probability in a distributed manner in OBS networks. Further, through theoretical analysis and simulations, we show that the proposed algorithms converge quickly on a sudden traffic increase in the network.

The Optical burst switching (OBS) networks have been attracting much consideration as a promising approach to build the next generation optical Internet. Aggregating the burst in the OBS networks from the high priority traffic will increase the average of the loss of its packets. However, the ratio of the high priority traffic (e.g. real-time traffic) in the burst is a very important factor for reducing the data loss, and ensuring the fairness between network traffic types. This paper introduces a statistical study based on the significant difference between the traffics to find the fairness ratio for the high priority traffic packets against the low priority traffic packets inside the data burst with various network traffic loads. The results show an improvement in the OBS quality of service (QoS) performance and the high priority traffic packets fairness ratio inside the data burst is 50 to 60%, 30 to 40%, and 10 to 20% for high, normal, and low traffic loads, respectively.

Parallel Optical Burst Switching (POBS) is a variant of Optical Burst Switching (OBS) which is proposed as a new optical switching strategy for Ultra-Dense Wavelength Division Multiplexing (U-DWDM) to support the enormous bandwidth demand of the next generation Internet. As opposed to OBS, POBS transmits bursts in two dimensions: the wavelength dimension and the time dimension. POBS network uses an one-way resource reservation mechanism to set up the resources for each data burst transmission. The use of this mechanism may cause bursts to contend for the same resources at the same time at core (intermediate) nodes of the network. Therefore, the performance of POBS networks depends on the contention resolution policies to reach acceptable levels for bandwidth usage. These policies may increase both the cost and complexities of the core nodes in POBS networks. Most literatures on OBS networks apply contention resolution at the core nodes based on reactive strategies that are activated after contention takes place in core nodes. This study proposes the use of a proactive contention resolution technique at ingress nodes of POBS network as well as reactive contention resolution technique at core nodes for reducing the probability of burst drop in the network in order to increase the performance of the network. The simulation results show that the use of POBS network with the proposed Reactive Odd/Even Node ID Wavelength Assignment Technique (POBS-ROENIDWAT) shows a better performance in terms of reduced data loss rate and increased throughput compared to the performances of both POBS network with Sequential Wavelength Assignment Technique (POBS-SWAT) and OBS network with Burst Segmentation (OBS-BS).

Optical Burst Switching (OBS) is a promising switching technology for the next generation all-optical networks. An OBS network without wavelength converters and fiber delay lines can be implemented simply and cost-effectively using the existing technology. However, this kind of networks suffers from a relatively high burst loss probability at the OBS core nodes. To overcome this issue and consolidate OBS networks with QoS provisioning capabilities, we propose an absolute QoS differentiation scheme, called Absolute Fair Quality of service Differentiation (AFQD), which is based on a wavelength partitioning scheme, called Optimization Topology-aware Wavelength Partitioning scheme (OTWP). AFQD is the first absolute QoS provisioning scheme that guarantees loss-free transmission for high priority traffic inside the OBS network. Simulation results show that AFQD not only guarantees loss-free transmission for high priority traffic but also substantially decreases the loss probability of best effort traffic to a remarkable level compared to the existing schemes.