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...     

带非线性光环路镜的光突发交换丢包率

OBS(光突发交换)的设计目的就是有效利用光纤提供的丰富带宽,突发冲突是光突发交换网络发展中遇到的主要问题之一.介绍一种新的突发冲突解决机制,这种方法是基于突发分段和NOLM(非线性光环路镜)的.NOLM与SOA(半导体光放大器)配合为分段的突发包提供光缓冲和超高速光交换服务.还对突发长度符合Pareto分布和负指数分布的突发源在不同的传输负荷下,采用该冲突解决机制时的突发包丢失率进行了计算仿真.     

光突发交换网络中基于突发包分段的联合冲突解决方法研究

光突发交换(OBS)技术由于结合了电的灵活处理和光的高速传输,成为构建下一代全光互联干线网最具前景的交换方式,其单向资源预留方式导致的突发包冲突是限制OBS走向实用的关键。基于突发包分段的光缓存冲突解决方法和基于突发包分段的波长转换冲突解决方法,首先通过对低优先级突发包进行分段解决冲突,然后对分段后冲突部分突发包进行光缓存或波长转换降低丢包率。对基于突发包分段的光缓存和基于突发包分段的波长转换两种冲突解决机制的性能进行了比较研究,仿真结果显示:两种机制都能够有效地降低整个网络的丢包率。当网络负荷较高时,采用基于突发包分段的光缓存方法对降低突发包的丢失率效果比较明显;当网络负荷较低时,采用基于突发包分段的波长转换方法能够更加有效地降低突发包的丢失率。     

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。     

E-OBS网络中一种基于优先级的抢占窗口机制

为了有效地降低突发包的丢失率和保证网络的服务质量,提出了模拟光突发交换网络中一种基于优先级的抢占窗口机制.该机制在模拟光突发交换核心路由器的控制信道上设置抢占窗口,以此来决定是否允许高优先级突发包抢占低优先级突发包.冲突发生时,系统判断高优先级突发包对应的控制包的到达时间是否满足抢占条件,如果满足抢占条件,则允许高优先...     

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。     

OBS中基于分割和波长转换的冲突解决机制

提出了一种"先分割后波长转换"的冲突解决机制。当冲突发生时,首先对低优先级突发包进行分割;不冲突部分直接在事先预留的输出数据信道上处理,冲突部分通过WC转换到空闲的波长信道上。仿真结果表明,高优先级突发包的丢失率比低优先级的要低,并且各优先级突发包的丢失率随核心节点WC转换度的增加而降低。     

OBS考虑优先级的突发包碎片可控合并重传算法

为了降低光突发交换网络中突发包的丢失率、降低网络路径的阻塞率、减小突发包冲突的概率,提出了考虑优先级的突发包碎片可控合并重传算法。当网络中数据通信发生冲突时,该算法能根据优先级进行突发包的分片,核心节点将这一信息反馈给边缘节点,边缘节点根据突发碎片的优先级以一定的概率重传被丢弃的突发包分片;同时,针对由于多次重传导致的突发包碎片过多的问题,该算法还按照突发包碎片的优先级顺序进行碎片重组,大大降低了网络的阻塞率。结果表明,相比以往的冲突解决算法,此算法在网络业务繁忙时的数据丢比特率和网络阻塞率方面的改善作用有比较明显的优势。这一结果对光突发交换网络的网络的性能改善方面是有帮助的。     

光突发交换网络中冲突性能分析

光突发交换(OBS)被认为是下一代光纤通信网络的典型代表.文章研究了在OBS核心节点中突发数据包由于竞争相同的输出数据信道而发生的冲突问题,对冲突时的网络性能进行了分析,得出了在不同网络负荷情况下的包丢失率情况,研究结果对OBS网络的实际建设有一定的理论指导意义.     

OBS网络核心节点冲突性能分析

对光突发交换(OBS)核心节点中突发数据包的冲突问题进行了性能分析,比以往同类研究改进之处在于,不仅给出了包阻塞率情况,还给出了OBS系统数据通过能力以及系统被占用均值等性能,结果对0BS冲突领域的研究进行了有益的补充和完善.     

OBS环网竞争解决办法的分析和比较

在光突发交换(OBS)基本概念的基础上,针对OBS网络,特别是OBS环网突发包竞争引起的突发包丢包等问题,介绍和比较了OBS网络中常用的突发包竞争解决办法.重点分析了几种适用于OBS环网的常用突发包竞争解决办法对网络吞吐量等主要性能的影响,指出了采用这几种竞争解决办法的网络的性能优劣,归纳总结了它们的优缺点.     

Dropping Policy with Burst Retransmission to Improve the Throughput of TCP Over Optical Burst-switched Networks

A major concern in optical burst-switched (OBS) networks is contention, which occurs when more than one bursts contend for the same data channel at the same time. Due to the bufferless nature of OBS networks, these contentions randomly occur at any degree of congestion in the network. When contention occurs at any core node, the core node drops bursts according to its dropping policy. Burst loss in OBS networks significantly degrades the throughput of TCP sources in the local access networks because current TCP congestion control mechanisms perform a slow start phase mainly due to contention rather than heavy congestion. However, there has not been much study about the impact of burst loss on the performance of TCP over OBS networks. To improve TCP throughput over OBS networks, we first introduce a dropping policy with burst retransmission that retransmits the bursts dropped due to contention, at the ingress node. Then, we extend the dropping policy with burst retransmission to drop a burst that has experienced fewer retransmissions in the event of contention at a core node in order to reduce the number of events that a TCP source enters the slow start phase due to contention. In addition, we propose to limit the number of retransmissions of each burst to prevent severe congestion. For the performance evaluation of the proposed schemes, we provide an analytic throughput model of TCP over OBS networks. Through simulations as well as analytic modeling, it is shown that the proposed dropping policy with burst retransmission can improve TCP throughput over OBS networks compared with an existing dropping policy without burst retransmission.     

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.     

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.     

A novel transfer mode to reduce burst loss rate for optical burst switching networks

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.     

Optimized Combination of Converter Pools and FDL Buffers for Contention Resolution in Optical Burst Switching

Optical burst switching (OBS) has attracted interest as a transport network architecture for the future optical Internet. As OBS relies on statistical multiplexing efficient contention resolution is a key issue in order to achieve a low burst loss probability. First, this paper discusses options and key design parameters for contention resolution in OBS. Then, it evaluates the performance of OBS nodes which employ shared wavelength converter pools and simple fiber delay line (FDL) buffers. Finally, optimized strategies for the order of probing a wavelength converter pool and an FDL buffer for contention resolution are presented and compared. It is shown that these strategies can be used to optimize performance for a given, for example, minimal cost, dimensioning of the wavelength converter pool and the FDL buffer.     

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.     

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.     

Node dimensioning in optical burst switching networks

Network dimensioning should be progressed for pursuing the ultimate efficiency of network system resources in order to satisfy target performance. This article studies node dimensioning as a method of resource optimization in optical burst switching (OBS) networks. OBS is a new switching technology for pursuing bufferless transparent optical networks by sending control packets prior to data burst in order to provision resources for the burst. However, the basic assumption of a bufferless node implies burst contention at a core node when more than two bursts attempt to move forward the same output simultaneously. Thus, burst contention is a critical performance metric and this article takes it into account as a constraint on node dimensioning and target performance. In this article, we first present node dimensioning issues for OBS networks. Two constraints from the transport plane and the control plane which affect burst contention are then introduced. The effect of the burst assembly process on node dimensioning is also presented. From numerical analysis, the optimal number of wavelengths in a link, which provides the lowest blocking probability, is obtained to suggest a guideline for node dimensioning.