Performance enhancement of optical burst switched networks

Optical burst switching (OBS) is an optical switching paradigm which offers a good tradeoff between the traditional optical circuit switching (OCS) and optical packet switching (OPS) since it has the relatively easy implementation of the first and the efficient bandwidth utilization of the second. Hence, OBS is a promising technology for the next generation optical Internet. A buffer-less OBS network can be implemented using ordinary optical communication equipment without the need for either wavelength converters or optical memories. In an OBS network, burst-loss performance is a critical concern. In OBS, the data-burst transmission is delayed by an offset time (relative to its burst control packet (BCP), or header) and the burst follows its header without waiting for an acknowledgment for resource reservation. Thus, a burst may be lost at an intermediate node due to contention, which is generally resolved according to the local routing and bandwidth information. The routing table maintained in each OBS node is generally pre-computed and fixed to forward the data bursts. Such a static forwarding feature might have limited efficiency to resolve contentions. Moreover, a burst may be lost and the network may be congested when a network element (e.g., fiber link) fails. In this paper, an efficient integrated scheme based on dynamic routing and burst segmentation has been proposed to improve reliability of data transport and network load balancing in optical burst switched networks. Simulation results demonstrate that the proposed approach reduces effectively blocking probability and hence contention. Further, it provides end-to-end throughput performance also. Hence, it establishes an appropriate tradeoff between loss rate and end-to-end throughput.     

OBS网络中基于优先级与突发包分割的偏射路由机制

为了有效地降低突发包的丢失率和保证OBS网络中不同优先级业务的服务质量,提出了一种基于优先级与突发包分割的偏射路由机制.当冲突发生时,首先基于突发包的优先级进行"竞争突发包头部分割或者原突发包尾部分割"处理;无冲突部分直接在事先预留的输出数据信道上处理,冲突部分的分割突发包根据参数可调的偏射路由机制被偏射到最佳偏射路径上.仿真结果表明,该机制能够有效地降低整个网络的丢包率和端到端的延时,并且得到高优先级突发包的丢失率和延时低于低优先级突发包.由此可知,基于优先级与突发包分割的偏射路由机制能够有效地解决突发包的冲突问题,从而提高整个OBS网络的性能.     

Integrated Contention Resolution and Control Algorithm for Optical Burst Switched Networks

Abstract

This article compares the conventional and proposed integrated contention resolution and control algorithm in optical burst switching with respect to burst loss probability and network throughput. Results have shown that the proposed approach behaves well in practice and responds quickly to any change in network status, while improving the overall network performance. It is shown that the proposed algorithm (ICRCA) not only provides significantly better burst loss performance than the conventional algorithms, but is also void of any packet re-orderings.     

An optimal burst assembly approach employing traffic shaping (OBATS) for OBS

Optical burst switching (OBS) aims at combining the strengths of packet and circuit switching and is considered as a promising technology for implementing the next generation optical Internet, required to cope with the rapid growth of Internet traffic and the increased deployment of new services. In this paper, an optimal burst assembly approach employing traffic shaping (OBATS) for OBS networks has been proposed in order to improve network performance in terms of reduced blocking probability, congestion control and better utilization of bandwidth. Particularly, the proposed scheme aims at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. Simulation results show that the proposed burst assembly approach gives better network performance in terms of burst drop, resource contention and delay as compared to conventional burst assembly approaches.     

Analysis of burst/packet assembly techniques in high-speed optical switching network

In the Optical Burst Switching (OBS) Network, the burst assembly technique is one of the challenging issues in the implementation of the system. It has the influence on the burst characteristic, which gives an impact on the network performance. Burst assembly is the process of assembling incoming data from the higher layer into bursts at the ingress edge node of the OBS network. The burst assembly mechanism must then place these packets into bursts based on some assembly policy. In this paper, the OBS system performance has been observed in simulated 12-node network based on Just-Enough-Time (JET) reservation protocol with various burst assembly techniques under the standard drop policy (DP) and the segmentation policy for contention resolution. The simulation results show that the performance of the proposed Adaptive-Threshold with Fixed Maximum Time Limitation (ATH-FMTL) burst assembly scheme is better than conventional burst assembly schemes in terms of loss probability and average assembly delay. Also, the proposed scheme avoids a sudden increase in the burst size and makes the burst sent out smoother as compared to conventional schemes.     

An optimal protection and restoration scheme (OPARS) for optical networks

Protection and restoration are critical network design issues for optical networks since even a single failure for a short duration may result in huge data loss due to the large capacity of optical fibers. However, few studies have been done on these issues for optical burst switching (OBS) networks. Protection and restoration are essential mechanisms for guaranteeing more reliable traffic delivery services. But it is not easy to apply existing mechanisms to optical burst switching (OBS) networks due to its one-way reservation signaling and the statistical burst multiplexing. Thus, to achieve the high transmission performance and reliability simultaneously, unique properties of OBS must be considered in the design of protection scheme. In this paper, an optimal protection and restoration scheme (OPARS) has been introduced that not only optimizes the number of provisioned protection wavelengths adaptively based on the traffic load as well as the quality of service (QoS) requirements of bursts in high speed networks but also minimizes burst loss rates. In addition, the proposed scheme has been used as an efficient contention resolution technique. The simulation results verify that the proposed scheme improve the network resource and channel utilization while guaranteeing the targeted protection reliability and QoS requirements of bursts.     

A maximum-efficiency-first multi-path route selection strategy for optical burst switching networks

In this paper, the impact of a path selection on other existing paths in optical burst switching (OBS) networks is studied by analyzing the contention among different traffic streams and the interaction between the route selection and traffic load balance. The results show that there exists a mutual reinforcement interaction among the traffic load of a path, the path burst loss ratio and the contention ability of the path when burst loss ratio based multi-path selection strategies are adopted, which may increase the unbalance of traffic and lead to severe congestion further. A maximum-efficiency-first multi-path selection strategy, which considers the performance of the burst flows and the impact of a path selection on existing OBS paths at the same time by a combined metric of route efficiency, is proposed to maximize the utility of the burst flows and minimize the increment of lost throughput on the path. The performance of the proposed multi-path selection strategy is evaluated through simulation. The results show that the presented strategy obviously outperforms the least burst loss ratio strategy and shortest path first strategy in terms of the burst loss ratio in the practical unbalanced background traffic, especially when the network is heavily loaded.     

A novel differentiated services supporting scheme for optical burst switched networks

In this letter, we analyze the drawback of tail-dropping contention resolution in optical burst switched networks. Once contention occurs, we adopt modified head-dropping policy to resolve contention. This policy drops the head of the contending burst only if the overlapping region of the two bursts is less than the whole contending burst size, otherwise drops the whole contending burst. In order to have a better support of differentiated service, a new burst assembly policy, namely, Priority-based proportional mixed burst assembly, is proposed. Simulation results show that the proposed scheme performs very well in terms of performance metrics such as the times of contention and packet loss probability.     

Congestion prevention for reliable OBS

It is known that Internet traffic exhibits a structural self-similarity over a wide range of time scales. Existing performance evaluation studies in optical burst switching (OBS) networks show high contention performance degradation in the nodes under correlated traffic. Due to its buffer-less nature, OBS efficiency can be reduced by resource contention leading to burst loss. Several methods have been proposed to address this problem, most of them relying on reactive mechanisms, which increase the complexity of core nodes, hampering scalability. In this paper to have congestion prevention, an efficient scheme incorporating delayed reservation decision has been proposed which not only offers reduction in resource contention by maintaining the same node complexity as that in general OBS networks with optical buffers but also provides improvement in system's throughput. Simulations show the proposed scheme has better performance than existing schemes in terms of burst loss probability.     

A new flexible and enhancing bandwidth utilization burst dropping technique for an OBS network

Optical burst switching (OBS) has been proposed as a competitive hybrid switching technology to support the next generation optical Internet. However, due to their one-way resource reservation mechanism, OBS networks experience high bursts (thus packets) loss rate. In OBS networks, the contention is resolved either by dropping one of the contending bursts or more efficiently by dropping from one of the contending bursts only the parts that overlap with the other bursts. In both situations, only one data source will suffer the data loss in favor to the other. In this paper, a new burst flexible and enhancing bandwidth utilization burst dropping technique has been proposed for contention resolution in optical burst switched networks. When contention occurs, any part of a contending burst could be dropped, instead of only the head or tail of bursts. The proposed dropping scheme makes bandwidth utilization more efficient and flexible. Simulation results show that the proposed dropping scheme performs better than existing burst dropping schemes.     

OBS网络中一种基于优先级和门限的偏射路由算法

为了解决偏射算法在偏射控制上的问题,提出了一种基于优先级和门限的偏射路由算法.该算法采用丢弃少量偏射的高优先级分割突发数据包来保证偏射路由上低优先级非偏射突发数据包的QoS.当冲突发生时,分割偏射优先级低的突发数据包,从而保护高优先级突发数据包|在偏射路由上,通过启用偏射检测函数来判断是允许偏射的分割突发数据包抢占资源或是丢弃偏射的分割突发数据包.仿真结果表明,虽然该算法增加了少量的端到端的传输时延,但这种算法可以很好地控制偏射突发对网络偏射路由上正常流量的影响,并且能够有效地降低整个网络的丢包率,很好地保护高优先级突发数据包的完整性.故这种方法能够有效地提高OBS网络的性能.     

光突发交换中支持区分业务的混合封装和改进的头部丢弃策略

介绍一种在光突发交换网中支持业务QoS,并减少分组到达乱序的突发包混合封装机制.通过将不同级别的分组组成相对独立的段,并进而封装到同一个突发包里,可减少分组到达乱序.结合改进的头部丢弃策略,可克服尾部丢弃法中存在的虚假冲突问题,能真正改善分组丢弃率.仿真结果表明,混合封装在结合改进的头部丢弃法之后,能很好地应用于具有QoS要求的光突发交换网中.     

光突发交换网中一种新的有优先权的冲突解决方案

提出了一种解决不同优先级突发包之间资源竞争的方案,分析了该方案下不同优先级的性能(时延和丢包率) .研究结果表明：高优先级突发包的平均时延和丢包率都远小于低优先级突发包,因此该方案能为高优先级突发包提供很好的QoS保障.     

Contention reduction and service differentiation in OBS networks

Optical burst switching (OBS) has been proposed to be a competitive switching technology for wavelength division networks (WDM) networks. In this switching technique, single burst loss due to contention influences loss of multiple data. Thus, burst loss ratio (BLR) is the main deciding factor for determining the performance of an OBS network. Also, inefficient data channel scheduling algorithm causes burst loss in OBS. In addition to this, the same service to all model of the current Internet is inadequate for the diverse quality of service expectations of Internet applications and users. In this paper, an efficient technique is proposed in which data burst is assembled from several Internet protocol (IP) packets in such a manner that the number of IP packets is changed according to the traffic load. In the proposed scheme, the burst is segmented because the segment located at the end of the contended burst has a greater chance of surviving contention (as the dropped segments are those at the beginning of the contending burst). Thus, the most important (or higher priority) information is enveloped in the last segmented. Further to prevent resource wastage due to over admitting of bursts, the proposed scheme is extended by admission control test for an output link without a fiber delay line (FDL) buffer. Also, modified latest available unscheduled channel with void filling (LAUC-VF) scheduling algorithm utilizing MPLS has been used to provide a scalable and manageable architecture for service differentiation (DiffServ) in IP networks. Simulation results demonstrate that the proposed technique has reduced burst loss rate and better quality of service (QoS) performance in comparison to existing techniques.     

An Algorithm for Contention Resolution in Label-Switched Networks

In this article, we are comparing two schemes of contention resolution, one through loopless deflection routing and other through criticality-based contention resolution. The comparison is done on the basis of packet loss probability and average delay in the network. The networks considered for analysis are NSFnet network and 6-node network.     

一种适用于光突发交换的区分型资源预留机制

将边缘结点突发汇聚算法与核心结点资源预留机制有机结合，提出了一种适用于光突发交换的区分型资源预留机制.引入“突发流”的概念，在边缘结点采用基于线性预测的突发汇聚算法将输入IP分组汇聚为单个突发或突发流；在核心结点引入“搭载请求”的思想，对单个突发和突发流采用不同的资源预留方案.仿真结果表明区分型资源预留机制可以明显改善光突发交换网络的丢失性能.     

A new burst assembly technique for supporting QoS in optical burst switching networks

This letter proposes a new burst assembly technique for supporting QoS in optical burst switching (OBS) networks. It consists of the adaptive-threshold burst assembly mechanism and QoS-based random offset-time scheme. The assembly mechanism, which is fit well to multi-class burst assembly, not only matches with IP QoS mechanism based on packet classification, and also utilizes fairly and efficiently assembly capacity. Based on token-bucket model and burst segment selective discard (BSSD), the offset-time scheme can smooth the traffic to support OBS QoS. The simulation results show that the technique can improve the performance in terms of packet loss probability (PLP).     

Blocking improvement for high priority in differentiated OBS networks through preemption and buffer-limitation

Delay preemption that combines the techniques of preemption and small buffers is an efficient solution for burst contention. However, due to the phenomenon of over-usage on buffer, the low-loss demand of high priority is not ensured especially in high traffic states. In this article, to improve the blocking of delay preemption, we propose a modified scheme named limited delay preemption based priority (limited-DPP) that constrains the buffered right of low priority within the moderate and high traffic states. To validate the efficiency of limited-DPP, the comprehensive analysis and simulation are performed in terms of loss and buffering time.     

A novel scheme of two-dimension time-stacked wavelength-time optical code label for optical packet switching network

A novel scheme of time-stacked optical code label based on optical code division multiple (OCDM) technique for optical packet switching network is proposed, in which two-dimensional wavelength-time OCDM code is used as the optical label. Packet loss rate and system characteristic based on the proposed scheme are studied. Results show that less packet loss rate of proposed scheme can be achieved as compared with that of one-dimension time-stacked optical code label system.     

一种基于分层的量子分组传输方案及性能分析

大规模量子通信网络中,采用量子分组传输技术能有效提升发送节点的吞吐量,提高网络中链路的利用率,增强通信的抗干扰性能.然而量子分组的快速传输与路由器性能息息相关.路由器性能瓶颈将严重影响网络的可扩展性和链路的传输效率.本文提出一种量子通信网络分层结构,并根据量子密集编码和量子隐形传态理论,给出一种基于分层的量子分组信息传输方案,实现端到端的量子信息传输.该方案先将量子分组按照目的地址进行聚类,再按聚类后的地址进行传输.仿真结果表明,基于分层的量子分组信息传输方案能够有效减少量子分组信息在量子通信网络中的传输时间,并且所减少的时间与量子路由器性能与发送的量子分组数量有关.因此,本文提出的量子分组信息传输方案适用于大规模量子通信网络的构建.