下一代网络与光交换

文章简述了用于下一代网络的交换技术,重点介绍了光交换技术,包括光分组交换、光突发交换与多协议波长交换.     

光分组交换技术的研究

光分组交换技术的引入，改善了带宽的利用率和网络的灵活性，延伸了光的透明性。在光分组交换层中光分组的产生、同步、缓存、再生，分组头重写及分光组之间挑功率的均衡成为实现光分组产换的基本技术，而多波长方案并不是光分组交换的唯一模式，光时分分组交换、光标签交换、波分及混合分组交换、多协议标签交换、光突发分组交换等交换方式的出现必将对未来的通信网产生重要的影响。     

光突发包交换关键技术概述

光突发包交换(OBS)技术是近年来出现的一种新型光交换技术，它结合了波长路由和光分组交换的优点，是一种未来一段时间内交换网络比较理想的过渡方案，为此介绍了OBS的基本原理，讨论了OBS中偏置时间的设置和交换信道的调度等关键技术，并就OBS的特点及仍需解决的问题作了总结。     

一种能有效支持QoS的光突发装配技术

提出了一种新的光突发装配技术，目的在于增强光突发交换(OBS)网络的服务质量(QoS)能力。该技术由自适应门限突发装配算法和基于优先级的随机化的偏移时间设置方案构成。该装配算法特别适合于多类别分组混合装配，能让所有类别的分组公平有效地使用装配能力，能较好地与IP层的QoS机制相匹配。偏移设置方案将突发控制分组(BCP)与突发数据(BP)间的偏移时间分成QoS偏移和随机偏移，前者由改进的JET协议按照有选择性的突发段丢弃机制(BSSD)确定，后者则由令牌桶机制确定。BSSD仅丢弃包含有低类别分组的突发段，而非整个突发。计算机仿真结果表明，本文提出的突发装配技术在性能上具有优越性。     

光突发交换网络中基于波长分集的QoS算法

光突发交换(Optical Burst Switching, OBS)被公认为是构建下一代光网络的有效交换技术。在OBS网络中有效地支持QoS (Quality of Service)是一个很重要的问题。该文从波长分集的思想出发,提出了几种适合OBS的QoS算法。这些算法可以根据各个优先级业务的变化情况,动态地调整各个优先级的业务使用的波长数目。通过仿真,并和已有算法相比,说明所提出的算法可以更好地提供区分服务,同时有效提高信道的利用率,降低整体的丢失率。     

利用GMPLS实现光突发交换

DWDM技术虽然可以实现较大的传输容量，但是在对信息进行处理的过程中，却存在着电子瓶颈，传统网络仍然需要在交换节点处对数据进行电的交换处理，从而降低了网络的交换处理速度。为了实现在光网络上直接传送数据业务，人们提出三种IP over DWDM网络方案：波长路由交换光网络、突发交换光网络和分组交换光网络。     

IP over WDM网中的QoS机制分析

IP网络提供的传统Qos(服务质量)机制很难应用到全光网络，这主要是因为在电域中电子包交换设备具有存储转发功能。能够在连接过程中通过排队和缓冲分组包来操纵网络带宽的竞争，而光域交换设备没有这样的功能。由于IP网是“尽力而为”的。IP over WDM网络需要建立QoS保障机制。而建立这些机制必须考虑到光域的物理特性和限制，因此介绍了当前IP over WDM网中几种典型的QoS实施方案，主要表现为波长路由、光分组交换和光突发交换三种光交换模型。     

光突发交换与下一代互联网

光突发交换与交换粒度介于光电路交换（即波长交换）和光分组交换之间的一种光交换模式，因为它克服了光电路交换和光分组交换的缺点，具有很大的技术优势，很有可能成为下一代互联网骨干网络的核心技术，真正实现光子互联网。本介绍光突发交换技术的基本原理，讨论了光突发交换的协议，突发封装和在IP骨干网中的应用等问题，并指出在这项技术得到应用之前需要解决的诸多课题。     

光突发交换技术

介绍了一种很有发展潜力的新交换模式－－光突发交换。对其基本概念、交换原理、网络结构、节点结构进行了简明的阐述,通过与另外两种典型交换模式－波长路由与光分组交换的比较,总结了光突发交换的优势,并指出了光突发交换尚待解决的问题。     

几种光域上的交换技术及其特点

随着电传送网技术向光传送网技术的演进.光层的联网能力越来越强,出现了几种光域上的交换技术:光线路交换/波长路由、光分组交换、光突发交换及为解决光分组在传送时出现丢失而重组时出现次序混乱等问题提出来的一种新颖的光分组流交换技术。下文将对这几种交换技术及其特点进行逐一介绍。     

Absolute QoS differentiation in optical burst-switched networks

A number of schemes have been proposed for providing quality-of-service (QoS) differentiation in optical burst-switched (OBS) networks. Most existing schemes are based on a relative QoS model in which the service requirements for a given class of traffic are defined relative to the service requirements of another class of traffic. In this paper, we propose an absolute QoS model in OBS networks which ensures that the loss probability of the guaranteed traffic does not exceed a certain value. We describe two mechanisms for providing loss guarantees at OBS core nodes: an early dropping mechanism, which probabilistically drops the nonguaranteed traffic, and a wavelength grouping mechanism, which provisions necessary wavelengths for the guaranteed traffic. It is shown that integrating these two mechanisms outperforms the stand-alone schemes in providing loss guarantees, as well as reducing the loss experienced by the nonguaranteed traffic. We also discuss admission control and resource provisioning for OBS networks, and propose a path clustering technique to further improve the network-wide loss performance. We develop analytical loss models for the proposed schemes and verify the results by simulation.     

Providing service differentiation for optical-burst-switched networks

This paper proposes a service differentiation scheme called preemptive wavelength reservation protocol (PWRP) to provide proportional quality of service (QoS) for optical-burst-switched (OBS) networks. In the context of service differentiation, traffic is divided into different service classes based on traffic characteristics. A service differentiation scheme then provides different degrees of resource assurance to different classes of traffic in proportion to their service classes. Unlike existing approaches, which may degrade to classless schemes or which may suffer from low wavelength utilization, the mechanism in this paper is robust and efficient and supports an incremental deployment of QoS support. A usage profile for each class is maintained at the router, and a preemptive wavelength reservation mechanism is implemented to ensure QoS. An analytical model is derived and simulations are conducted to evaluate the performance. The results show that the approach described in this paper performs better than existing mechanisms in terms of lower blocking probability and higher resource utilization, making it an excellent QoS mechanism for OBS networks.     

Priority-based offline wavelength assignment in OBS networks

Optical burst switching (OBS) is a promising technique for wavelength division multiplexing (WDM) networks. In practice, wavelength converters (WCs) are either absent or only sparsely deployed in WDM networks due to economic and technical limitations. Thus, wavelength assignment is expected to be an important component of OBS networks. In this paper, an offline wavelength assignment scheme in OBS networks without wavelength conversion capability is proposed. The key idea of the scheme is to decide the wavelength searching order of each traffic connection at edge nodes according to the wavelength priorities determined by the calculated burst loss probabilities on different wavelengths. Simulation results indicate that the proposed scheme can reduce the network-wide burst loss probability significantly compared with other schemes. It is also illustrated that the performance of the proposed scheme can be further enhanced by a larger number of wavelengths per link and a reasonable delay bound at edge nodes.     

A new scheduling algorithm to provide proportional QoS in optical burst switching networks

A new scheduling algorithm, which aims to provide proportional and controllable QoS （Quality of Service） in terms of burst loss probability for OBS （Optical Burst Switching） networks, is proposed on the basis of a survey of QoS schemes in current OBS networks. With simulations, performance analysis and comparisons are carried out in detail. The results show that, in the proposed scheme, burst loss probabilities are proportional to the given factors and the control of QoS performance can be achieved with better performance. This scheme will be beneficial to the OBS network management and the tariffpolicy making.     

Loss differentiation in OBS networks without wavelength-conversion capability

Service differentiation is an open research issue in OBS networks. Most proposals assume full wavelengthconversion, but wavelength converters are still very complex and expensive. We propose the QoS Multiple Wavelength Simultaneous Transmission technique (QoS-MWST), a novel method for providing loss differentiation in OBS networks without wavelengthconversion capability (or even limited capability). In QoS-MWST, multiple copies of each burst are simultaneously sent on different wavelengths, and loss differentiation is achieved by properly sending more copies of the higher-priority bursts. Through analysis and simulation, we prove that QoS-MWST can efficiently provide loss differentiation in this type of OBS networks.     

Contour-Based Priority Scheduling in Optical Burst Switched Networks

Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over dense wavelength division multiplexing links. Although several quality-of-service (QoS) schemes have been proposed for OBS networks, how to provide QoS at the high speed required by the OBS network is still an open question. In this paper, we propose a novel O(1) runtime contour-based priority algorithm that provides complete priority isolation among different priorities. This is the first practical O(1) runtime priority algorithm proposed for OBS, and it is well suited to high-speed hardware implementation.     

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。     

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.     

A novel contention solution strategy based on priority for optical burst switching networks

A fundamental issue in optical burst switching (OBS) networks is to solve the burst contention for the core node. In this paper, a novel priority-based contention solution strategy for OBS networks is proposed. When the contention occurs, the burst priority is considered firstly, and then the burst segmentation method is used for the low priority bursts in this strategy. Ensuring the integrity of high priority bursts, part of the segmented bursts can be transmitted to the destination node via combining wavelength conversion and optical buffer method. Simulation results show that the proposed scheme not only ensures the integrity of high priority bursts, but also reduces the packet loss rate of the low priority bursts maximally, so that it can support good quality of service (QoS) for the network.