A Limited Deflection Routing Algorithm Based on Burst Loss Threshold in OBS Networks

1 Introduction The increase in the demand of transport capacity duetothe explosive growth of the Internet IP-based traffichas fueled the development of high-speed transmissionsystems andthe emergence of Wavelength Division Mul-tiplexing ( WDM) technology[1].Soin the near future ,it will be possible to support hundreds of wavelengths ofseveral Gigabit/s each. A new approach called OpticalBurst Switching (OBS)[2]that combines the best of op-tical circuit switching and optical packet switch…     

一种基于门限的光突发交换受限偏射路由算法

提出了一种基于突发丢失门限的条件偏射路由算法（LDFD），该算法采用丢弃少量偏射的高优先级突发来保证偏射路由上较低优先级非偏射突发的服务质量（QoS）。当偏射的高优先级突发到达核心节点而该节点没有空闲数据信道时，就启用定义的偏射条件检测函数来判断是丢弃该突发还是允许其抢占非偏射的低优先级突发的资源，从而减少偏射突发与偏射路由上原有突发的竞争。仿真表明，该算法可以很好地控制偏射突发对偏射路由上正常流量的影响，并有效地提高整个网络的突发丢失性能。     

OBS中基于优先级与负载均衡的偏射路由算法

为了解决偏射算法在偏射控制七的问题,提出了一种基于优先级与负载均衡的偏射路由算法.当冲突发生时,分割优先级低的突发数据包;将冲突部分的突发包偏射到空闲的链路上,并在空闲的链路中选择若干条"当前最大剩余跳数小于源-目的节点的最大跳数"的路由作为候选路由;最后,在这些候选路由中选择一条可以使网络中各链路使用波长数的统计方差...     

Dynamic Deflection Routing with Virtual Wavelength Assignment in Optical Burst-Switched Networks

In optical burst-switched networks, one of the most significant issues is contention resolution. There have been several deflection routing techniques as contention resolution. While contention is resolved by traditional deflection routing, it cannot guarantee that the control packet will reserve all the wavelengths successfully to the destination on the alternate path, especially when traffic load in a network is high. Therefore, in this paper, we propose a Deflection Routing with Virtual Wavelength Assignment (DR-VWA) algorithm in order to provide a higher resource guarantee for loss-sensitive traffic bursts. The proposed DR-VWA scheme (1) dynamically decides the alternate path with the least traffic load and (2) allows high-priority bursts in terms of loss to be assigned available wavelengths over the path virtually. The proposed scheme is evaluated through simulation, and it is shown that significant improvement with regard to burst loss and wavelength conversion cost can be achieved.This work was supported in part by the Korea Science and Engineering Foundation (KOSEF) through OIRC project and by the US National Communications System (NCS).     

A Study on Deflection Routing in Optical Burst-Switched Networks

A major concern in optical burst-switched networks is contention,which occurs when multiple bursts contend for the same link. While a deflection routing protocol is proposed as one of the contention resolution techniques,there has been no appropriate deflection routing algorithm to find an alternate route. In this paper, we formulate a deflection routing problem based on the burst blocking rate resulting from resource contention in an optical burst-switched network. This algorithm minimizes the contention on the alternate path with the minimum distance. Furthermore, in this paper, we develop an analytical model for the deflection routing time when deflection routing is performed to resolve contention. In this model, we investigate the expected deflection routing time considering that the burst could be dropped even with deflection routing due to another contention on the alternate path. Simulations are conducted to show that there is an improvement in terms of burst loss rate and network throughput.     

A distributed backoff-channel deflection algorithm with load balancing for optical burst switching networks

Optical burst contention is one of the major factors that cause the burst loss in the optical burst switching (OBS) networks. So far, various contention resolution schemes have been proposed. Among them, the deflection path is more attractive due to its low requirement for optical buffer in capability and quantity. However, these deflection path algorithms do not consider the successful transmission rate of deflection traffic, and the deflection traffic??s impacts on the original traffic of the deflection path are not concerned. Meanwhile, the offset-time deficit problem for deflected bursts is ignored. Therefore, in order to reduce the burst loss probability in OBS networks, a Distributed Backoff-channel DeFlection algorithm with load balancing, for short DBDF-LB, is proposed. It consists of two parts, that is, the deflection with load balancing and the backoff-channel buffering scheme. Firstly, from the perspective of the network-wide load balancing, the optimal deflection path, on which the contention-failure burst is deflected with the minimum hops and the least burst loss probability, is selected. Secondly, the extra offset-time for the deflected burst is provided through the backoff-channel scheme. Finally, by numerical simulations, compared with the classical shortest path deflection algorithm, the DBDF-LB can obviously reduce the burst loss probability, about 50%, with a little extra overhead.     

基于竞争控制的光突发交换条件偏射路由算法

光突发交换(OBS)网络中,偏射路由算法是有效地解决突发竞争、提高网络性能的一种重要措施,但通过分析发现,它可能会导致偏射路由上正常(非偏射)突发的丢失率上升.提出了一种基于竞争控制的条件偏射路由算法,根据定义的偏射条件检测函数,有条件的偏射或丢弃竞争突发来保证偏射路由上正常突发的QoS.仿真表明该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.     

光突发交换网络新型偏射路由方案研究

光突发交换(OBS)被认为是下一代光网络中的有效核心交换技术之一,设计OBS网络的最初目的之一是减小突发包丢失率.解决突发竞争的方法主要包括光缓存、波长变换、偏射路由和突发分段.提出一种改进偏射路由方案,并建立了数学模型,对改进方案的性能进行了仿真分析,结果表明改进方案能更好的提高网络整体性能.     

A dynamic load-aware congestion control scheme in optical burst switching networks

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.     

OBS网络中基于拥塞避免的提前偏射路由研究

突发竞争是OBS(光突发交换)网络需要解决的关键问题,偏射路由作为一种有效的竞争解决方案而被广泛研究。文章提出了一种基于拥塞避免的提前偏射路由算法,利用周期性反馈的网络拥塞信息按一定概率提前偏射部分突发包。与传统的最短偏射路由算法相比,本算法达到了避免拥塞以及均衡网络负载的目的。仿真结果表明:文章所提算法在突发丢失率、吞吐量以及平均链路利用率方面性能都有所提高。     

Contention resolution considering multicast traffic in optically burst-switched WDM networks

This paper proposes a contention resolution scheme considering multicast traffic in optical burst switching (OBS) networks. In OBS networks, for unicast bursts, contention can be avoided by deflection routing. However, deflection routing cannot be applied to multicast bursts because multicast bursts are transmitted along light-trees which are fixed, tree-shaped routes. Therefore, the loss probability of multicast bursts is generally high. To resolve this problem, the proposed scheme introduces an ingenious offset time assignment strategy which completely avoids contention of multicast bursts due to transmissions of unicast bursts by strategically assigning additional offset times. Furthermore, in the proposed scheme, unicast bursts avoid contention with deflection routing. Through simulation experiments, we show that the proposed scheme improves the loss probabilities of both of unicast bursts and multicast bursts.     

A burst segmentation-deflection routing contention resolution mechanism in OBS networks

One of the key problems to hinder the realization of optical burst switching(OBS) technology in the core networks is the losses due to the contention among the bursts at the core nodes.Burst segmentation is an effective contention resolution technique used to reduce the number of packets lost due to the burst losses.In our work,a burst segmentation-deflection routing contention resolution mechanism in OBS networks is proposed.When the contention occurs,the bursts are segmented according to the lowest packet loss probability of networks firstly,and then the segmented burst is deflected on the optimum routing.An analytical model is proposed to evaluate the contention resolution mechanism.Simulation results show that high-priority bursts have significantly lower packet loss probability and transmission delay than the low-priority.And the performance of the burst lengths,in which the number of segments per burst distributes geometrically,is more effective than that of the deterministically distributed burst lengths.     

一种支持业务均衡的OBS自适应多可达性路由机制

针对光突发交换(OBS)网络中如何高效解决频繁发生的光突发竞争问题,提出了一种支持业务均衡的OBS自适应多可达性路由机制(AMR-LB).首先根据发送端发送业务量大小和当前网络业务承载状态,按需地为光突发确定多可达性路由;然后在非线性规划下,自适应地调整各条路由的业务承载比例.通过性能仿真,并与自适应替代路由算法(AA...     

Contention-Based Limited Deflection Routing Protocol in Optical Burst-Switched Networks

Optical burst switching (OBS) is a very promising switching technology for realization of an economical optical Internet. In OBS networks, when contention occurs at an intermediate switch, two or more bursts that are in contention can be lost because a forwarding path reservation is not made for a burst until a control message for the burst arrives. That is the reason why one of the critical design issues in OBS is finding ways to minimize burst dropping resulting from resource contention. In this paper, we propose and analyze a novel deflection routing protocol, which mitigates and resolves contention with significantly better performance as compared with techniques currently known in the literature. While several variants of the basic deflection routing scheme have been proposed before, they all lacked the ability to determine the alternate route based on clear performance objectives. In this paper, we present an on-demand deflection routing scheme, which sequentially performs the following: 1) based on certain performance criteria, dynamically determines if the burst should be deflection routed or retransmitted from source and 2) if the decision is to deflection route, then the same is done using a path that is based on minimization of a performance measure that combines distance and blocking due to contention. The proposed contention-based limited deflection routing scheme prevents injudicious deflection routing. Our simulation results show that the scheme proposed here has much superior performance both in terms of burst loss probability and increased network throughput. Through analytical and simulation modeling, a number of useful insights into the OBS network protocols and performance are provided.     

TCP over optical burst-switched networks with controlled burst retransmission

For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, the loss of bursts can lead to serious degradation of TCP performance. Due to the bufferless nature of OBS, random burst losses may occur, even at low traffic loads. Consequently, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network. The TCP sender will then trigger congestion control mechanisms, thereby reducing TCP throughput unnecessarily. In this paper, we introduce a controlled retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can reduce the burst loss probability in the OBS core network. Also, the OBS retransmission scheme can reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We develop an analytical model for evaluating the burst loss probability in an OBS network that uses a retransmission scheme, and we also analyze TCP throughput when the OBS layer implements burst retransmission. We develop a simulation model to validate the analytical results. Simulation and analytical results show that an OBS layer with controlled burst retransmission provides up to two to three orders of magnitude improvement in TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-outs when the OBS retransmission scheme is used.     

光突发交换网络的拥塞控制技术研究(本期优秀论文)

光突发交换(OBS)技术能很好地支持突发业务,有希望应用于Internet核心交换.但是,OBS网络的单向预约信令方式容易造成网络拥塞和大量的突发丢失.文章在深入研究现有的OBS网络拥塞控制策略的基础上,提出了一种新的基于速率的OBS拥塞控制策略.边缘源结点向宿结点周期性地发送和接收资源管理分组(RMP),边缘源结点根据RMP中的拥塞反馈指示了解网络中的拥塞状况,并改变突发发送速率,从而解除拥塞.     

Hierarchical time-sliced optical burst switching

To overcome the need for large buffers to store contending bursts in optical burst switched (OBS) networks, a recent variant called time-sliced OBS (TSOBS) suggested that bursts be sliced and spread across multiple frames of fixed-length time-slots. Since TSOBS is rigid in its frame structure, this paper generalises TSOBS to allow a hierarchy of frames. Termed hierarchical TSOBS (HiTSOBS), this scheme supports several granularities of rates, and permits multiple traffic classes with different loss-delay requirements to efficiently share the network. Our contributions are as follows: first, we present an architecture for HiTSOBS and offer it as a viable option for the realisation of flexible and cost-effective OBS networks. Second, we develop mathematical analysis to study the loss and delay performance of the proposed HiTSOBS system. Finally, we present simulation results that captures these loss-delay tradeoff values. Our HiTSOBS architecture gives network operators the freedom to choose the right mix of traffic with desired loss-delay requirements to coexist in the network.     

OBS网络中的新型竞争解决方案

提出一种解决光突发交换(OBS)网络节点中突发数据包冲突的方案.发生冲突时,在OBS层重传被丢弃突发数据包,然后给出评估这种重传机制丢包率的方法,并与偏射路由策略的性能进行比较,结果表明突发重传机制显著改善了丢包率.可以很好地实现服务质量(QoS)机制.     

Impairment-aware ordered scheduling in dual-header optical burst switched networks

Optical burst switching (OBS) is a promising technology for bridging the gap between optical wavelength switching and optical packet switching. Optical signal transmission quality is subject to various types of physical impairment introduced by optical fibers, switching elements, or other network components. The signal degradation due to physical impairment may be significant enough such that the bit-error rate of received signals is unacceptably high at the destination, rendering the signal to not usable. In this article, based on earlier study, we study the burst-scheduling problem in OBS networks using two control packets for each data burst, taking into account physical impairment effects. We propose a burst-scheduling algorithm that accommodates incoming bursts by primary path routing, deflection routing, and burst scheduling. We design an admission control mechanism to use network resources efficiently. At an OBS node, the proposed algorithm schedules bursts for transmission by searching for available resources as well as verifying signal quality. Our simulation results demonstrate that the proposed algorithm is effective in terms of reducing the burst-blocking probability.     

OBS网络的偏射路由研究

文章分析了偏射路由对网络性能的影响,在分析发送端控制偏射路由技术的基础上,提出了基于阈值检测和数据更新的改进方案.边缘节点快速更新状态信息,并通过特殊控制分组传递链路拥塞的分布特征等信息;交换节点进行阈值检测,动态决定竞争时突发的传送方式,减少偏射路由对网络负荷的影响,进一步降低网络阻塞率,改善网络性能。