OBS网络中一种基于突发包优先级分割的可控重传方案

在光突发交换(OBS)网络中,突发包会由于竞争OBS核心节点输出端口的有限波长资源而发生冲突。突发包重传能够在一定程度上减少由于突发包在核心节点冲突而导致的数据损失,但重传次数的增加可能会加重网络负荷,反而增加数据丢失率。并且,在多业务存在的OBS网络中,重传方案需要能够实现区分服务以保证网络的服务质量(QoS)。据此,本文提出一种基于突发包优先级分割的可控重传方案,在实施优先级分割的同时,根据网络负荷赋予每次重传不同的概率,并对重传次数加以控制。最后,仿真分析了路径阻塞率和不同优先级业务的字节丢失率(ByLP,byte loss probability)性能。     

基于部分冗余合并的OBS网络冲突解决机制

为了降低光突发交换网络中突发包的丢失率、减小网络延时、提高网络信道的利用率,采用了一种新型考虑优先级的基于冗余合并的突发包冲突解决机制。算法增加了回退信道作为保护信道,根据业务的优先级对冲突的突发包进行分段,使无法顺利传送的突发包碎片进入到回退信道;同时,考虑到网络中存在着很多短小而难以利用的信道资源,算法将回退信道里的突发包碎片进行多次克隆,多个克隆碎片和由上游节点到来的突发包合并成粒度可变的虚拟突发包发送,克隆碎片的优先级定义为最低,以保证不抢占正常突发包的信道资源。结果表明,相比以往的冲突解决算法,此算法具有较低的丢包率、相对小的延时率和优越的信道利用率。     

基于窗口的光突发交换调度算法

针对光突发交换网(OBS)中的资源竞争和QoS支持等问题，提出了一种新型的基于窗口的调度算法。该算法利用边缘节点的电缓存，对调度窗口中的突发数据包进行批量BORA调度，可以有效地降低网络中发生资源竞争的概率；同时调度窗口中的优先级策略还可以进一步增强QoS。网络仿真结果表明，通过选择合适的调度窗口和最大允许时延，该调度算法在0．8的网络负载下使得高优先级突发数据包的阻塞率下降一个量级，信道利用率提高3．5％。     

一种新颖的突发交换网络混合组装算法研究

提出一种新颖的混合组装算法来实现对到达网络边缘节点的IP数据进行突发组装.低流量时,采用FAP算法改善数据延迟特性;高流量时,采用AAS算法防止由于阻塞而产生的突发丢弃.仿真结果表明,混合组装算法在保证网络较低的阻塞率的同时,有效改善了数据突发在边缘节点的排队延迟特性.     

OBS基于回退和信道分级的冲突解决算法

解决突发包的冲突问题是光突发交换网络的关键技术之一。为了降低突发包冲突时丢包率,提出了一种新型的基于信道分级和回退机制的冲突解决算法,该算法考虑突发业务优先级,将信道分成两个级别,有区别地对待高低优先级两种业务类型,并且增加了一部分回退信道作为保护和重发冲突数据包,能够有效地保证高优先级业务的传输可靠性。结果表明,当冲突发生时,网络能根据此时高低优先级业务量的比重配比,自适应地调节两个级别信道的数量,兼顾到低优先级业务的低丢包率,保证了较低的延时率。此算法相比以往的冲突解决算法具有较低的丢包率和相对小的延时率。     

OBS网络中基于优先级与参数可调的偏射路由算法

为了保证OBS网络中不同优先级业务的服务质量和解决偏射算法在偏射控制上的问题,提出一种基于优先级与参数可调的偏射路由算法.该算法通过设置可调参数“偏射概率”来控制冲突突发包的偏射,并从可调丢包率和偏射路径长度意义上寻找最佳偏射路由.当冲突发生时,分割优先级低的突发包,并将分割突发包偏射到空闲的链路上;在空闲的链路中选择...     

OBS网络中基于优先级的先分割后缓存冲突解决方法

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的先分割后缓存冲突解决方法。该方法通过在多波长信道系统的输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包。当冲突发生时,首先基于突发包的优先级和处理完毕时间进行"竞争突发包头部分割或者原突发包尾部分割"处理;无冲突部分进行交换或者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进行光缓存。仿真结果表明,多波长信道系统中,高优先级突发包的丢失率低于低优先级突发包的丢失率。同时该方法在一定程度上可以有效地减少端到端的传输时延和整个网络的丢包率,从而提高整个OBS网络的性能。     

一种新的基于多节点网络编码的无线广播重传算法

提出了一种基于网络编码的无线网络广播重传算法。该算法按照包丢失分布概率的特点生成新的重传序列,采用多节点的网络编码方法进行丢失包组合实现重传。通过数学分析和仿真证明,该算法能保证接收节点的编码可解性,同时重传次数可达到局部最优性;与传统重传方法相比,该算法可以有效地减少信息包的平均传输次数,从而提高传输效率。     

一种基于突发分片技术的OBS竞争解决机制

介绍了基于光突发分片技术的竞争解决机制,着重对采用光突发分片技术与数据信道调度算法相结合的竞争解决机制进行了研究.通过建立相应的光突发交换网络仿真模型,对结合后的竞争解决方法与其他方法进行了性能比较.结果表明,将光突发分片技术与数据信道调度算法相结合能够有效地降低网络阻塞率,提高信道利用率,从而改善网络性能.     

光突发交换网络基于优先级与突发包分割的光缓存方法

为了保证光突发交换(OBS)网络中不同优先级业务的服务质量(Qos)和有效地降低突发包的丢失率,提出了一种基于优先级与突发包分割的光缓存方法.该方法通过在输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包.当冲突发生时,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;无冲突部分进行交换或者直...     

A framework of prioritized burst segmentation supporting controlled retransmission in OBS networks

In optical burst switching (OBS) networks, burst contentions in OBS core nodes may cause data loss. To reduce data loss, retransmission scheme has been applied. However, uncontrolled retransmission may increase network load significantly and data loss probability defeating the retransmission purpose. In addition, in a priority traffic existing OBS network, OBS nodes may apply different retransmission mechanisms to priorities bursts for quality-of-service (QoS) support. This study has developed a controlled retransmission scheme for prioritized burst segmentation to support QoS in OBS networks. Unlike previous works in the literature, we have set a different value to retransmission probability at each contention and propose a retransmission analytical model for burst segmentation contention resolution scheme. In addition, we have applied the proposed retransmission scheme to the prioritized burst segmentation for QoS support. We have taken into account the load at each link due to both fresh and retransmitted traffic, and have calculated the path blocking probability and byte loss probability (ByLP) for high-priority and low-priority burst to evaluate network performance. An extensive simulation has been proposed to validate our analytical model.     

Analysis of Burst Segmentation in Optical Burst Switching Networks Considering Path Correlation

One of the key problems hindering the realization of optical burst switching (OBS) technology in the core networks is the losses due to contention among the bursts at the core nodes. Such contention losses do not necessarily indicate a situation of congestion. Burst segmentation is an effective contention resolution technique used to reduce the number of packets lost due to the burst losses. In this work, we propose a method of analyzing the benefit of burst segmentation considering the effect of correlation in traffic across multiple paths. Starting with the cumulative distribution function (cdf) of the length of the bursts at the ingress node destined to a particular egress node, we evaluate the cdf of the burst length at each node along the path considering the probability of segmentation and the traffic on the adjoining paths. Comparing the burst length at the egress node with that at the ingress node, we evaluate the byte loss probability (ByLP) along the path and also the network-wide average ByLP. The proposed analytical framework studies the impact of segmentation on packet loss rate considering the effect of the length of a path, the number of paths adjoining a path (extent of path correlation), the effect of load on a path and other correlated paths, and the burst assembly algorithm. Analytical and simulation results in this work show that the proposed method of analysis gives a good understanding of the influence of aforementioned factors on the benefit of segmentation in OBS networks.      

Delay-on-Demand: A Signaling Protocol to Reduce Blocking Probability in Optical Burst-Switching Networks

Optical burst switching (OBS) is emerging as one promising switching paradigm for the next generation optical networks. To support multiple services in burst-switching networks, the OBS paradigm should support some quality-of-service (QoS) provisioning. A major design issue in such networks is to reduce the blocking probability of the bursts arising due to resource contention at the intermediate core router. In this paper, we propose a signaling protocol which we call ‘Delay-on-Demand’ (OBS-DoD), to reduce blocking probability and support QoS in optical burst-switching networks. The proposed scheme guarantees that at least one of the bursts succeeds depending on its priority, propagation delay from the ingress router, and the burst-size when contention occurs at the core router. For this, we use a control packet to delay, in case of a contention, the transmission of bursts at the ingress router. We compare the performance of our proposal, by simulation, with an earlier proposed scheme, and show that the proposed OBS-DoD outperforms the earlier scheme in reducing the blocking probability. For simulation, we generated bursty traffic using an M/Pareto distribution.     

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...     

Burst scheduling for differentiated services in optical burst switching WDM networks

Optical burst switching (OBS) is one of the most important switching technologies for future optical wavelength division multiplexing (WDM) networks and the Internet. The model of differentiated services has been proposed to support quality of service (QoS) in the IP‐based Internet. It is also very important to have differentiated service support in OBS networks. When the burst scheduling in an OBS network is set up appropriately, network can support differentiated services. In this paper, we proposed a new burst scheduling scheme, called differentiated scheduling with identical priority offset time (DSIPO). In DSIPO, the same priority offset time is used for all the bursts destined to the same edge node regardless of their priorities. Differentiated services in terms of burst loss probability are achieved by processing the control packets of higher priority class bursts, thus reserving resources for their data bursts, more promptly upon their arrival than those of lower priority class bursts. Each intermediate (core) node can adjust the burst loss probabilities of various burst classes by choosing its own differentiated processing delay value for each priority class or its own differentiated processing delay difference value between any pair of adjacent priority classes. We model and analyse DSIPO in terms of the burst loss probability for each priority class with simulation validation. The performance of DISPO is evaluated by simulation. Copyright © 2004 John Wiley & Sons, Ltd.