全光光孤子WDM到OTDM转换的概念系统

提出了在未来的光孤子波分复／时分复用网络中由ＷＤＭ到ＯＴＤＭ节点处的转换复用的概念系统，主要的模块是完成波长转换的基于交叉增益调制的半导体光放大器，同步和延时及时分复用模块。通过ＳＯＡ可以实现全光的ＷＤＭ到ＯＴＤＭ的波长转换复用，是ＷＤＭ／ＯＴＤＭ网络实用化的一个关键部分。     

突飞猛进的光通信技术

随着ＭＰＬＳ、ＤＷＤＭ、数字包封、波长选路及ＷＤＭ保护环网等新技术的开发,ＷＤ Ｍ光网络层已具有许多原先只能在高层实现的网络功能。原先单纯为了增加系统传输容量的ＷＤＭ技术,已转化为具有真正联网功能的多波长光网络技术,为彻底抛弃ＳＯＮＥＴ／ＳＤＨ,直接在具有光联网功能的 ＷＤＭ多波长光网络上承载 ＩＰ业务创造了条件。     

波分复用全光网络及其波长转换技术

波长转换是实现ＷＤＭ全光网络的关键技术之一。通过波长转换，可以减小由于波长竞争带来的阻塞概率，使网络所需滤长数变为最小，网络管理和控制更加灵活，并具有高的可靠性和可扩充性。基于半导体光放大器的全光波长转换技术具有大的优势。本文首先介绍了ＷＤＭ全光网络的概念，分层模型及其优势，然后指出滤长转换的重要性和技术要求，最后分别介绍了基于半导体光放大器的三种滤长转换器的原理、结构和各自的优缺点。     

光纤技术浅谈

信息的爆炸导致全球通信业务急剧增长 ,带给传输网络巨大的压力 ,ＷＤＭ技术的应用使带宽资源问题得以缓解 ,电信网络正朝着全光网络的方向迈进。１ＷＤＭ技术ＷＤＭ技术是将多路处在不同光波长上的信道合波后送入光纤中同一根纤芯进行传输 ,每一个光波长传输一个ＴＤＭ信号 ,只要各波长间有足够的间隔 ,就不会相互干扰。如果将各路光载波波长的间隔减小 ,则可在同一根光纤中同时传输更多路的光载波 ,这就是ＤＷＤＭ(密集波分复用 )技术。过去的ＷＤＭ仅指１３１０ｎｍ和１５５０ｎｍ的简单复用 ,ＤＷＤＭ指１５５０ｎｍ波长区域内的密集复…     

IP直接承载于WDM的全新技术方案

新技术的开发和使用为直接在ＷＤＭ光网络上承载ＩＰ业务创造了条件。本文在介绍了相关支撑技术的基础上研究了一种全新的ＩＰ ｄｉｒｅｅｔｌｙ ｏｖｅｒ ＷＤＭ的实现方案－－基于ＭＰＬＳ和多波长光网络的ＩＰ到ＷＤＭ的集成网络结构。     

智能光开关——实现全光网的关键

在光纤传输系统中,应用ＤＷＤＭ技术的目的是为了满足Ｉｎｔｅｒｎｅｔ及其它电信业务对带宽的爆炸性需求。单根光纤可同时传输的波长数已从几年前普通ＷＤＭ的８个波长增长到国前ＤＷＤＭ的约１６０个波长,其增加的容量相当于数十万路电话的容量。 然而,人们对容量和带宽的需求是永无尽头的,最终的目标是建设一个能达到以Ｔｂ／ｓ速率传输的全光通信网。 全光网络的关键要素是“透明”,即网络中的光交叉连接与光分插复用器件应与所传输的数据格式、比特率以及所使用的协议无关。有几种类型的光开关提供了这种透明性。 这种光开关不需…     

光码分多址技术在光接入网中的应用

无源光网络是光接入网的主要发展方向,ＦＴＴＨ是ＰＯＮ的最终方式,将ＯＣＤＭＡ,ＷＤＭ等技术用于光接入网中,是帝现接入网宽带化的途径之一。介绍了ＯＣＤＭＡ的技术报目前光接入网中多址技术的弊端,探讨了ＯＣＭＤＡ用于光接入网的可能性和优势,提出实现无源光网络多址接入的ＷＤＭ／ＣＤＭＡ方案。     

利用DWDM实现核心网络的光网络互联

光网络互联实现了综合ＩＰ、ＡＴＭ、ＳＯＮＥＴ／ＳＤＨ和ＤＷＤＭ技术的低成本网络。ＤＷＤＭ技术彻底改变了核心网络,在ＤＷＤＭ配置的第二阶段,ＩＰ路由器和ＡＴＭ设备直接连接到ＤＷＤＭ,省去了ＳＯＮＥＴ／ＤＳＨ和ＡＴＭ,降低了成本,简化了扩容。光网络互联多数利用了现有标准,但新技术、新网络元素的引入同多带来了互操作问题,因此必须建立开放的ＤＷＤＭ系统,这也将推动光网络互联标准的发展。     

全光网络的演进和发展

光通信采用的光复用技术主要有两种：时分复用（ＴＤＭ）和波分复用（ＷＤＭ）技术。对于ＴＤＭ来说，使用单一波长的光信号，光纤带宽易于控制；但缺点是传输容量要进一步增加时，必须把光脉冲压缩得更窄，就需有更高速和精密的光器件去保证。对于ＷＤＭ来说，各信道的速率相对较低，不必设置精密的定时电路。一根光纤如只传输一路光信号，只限于４０Ｇｂｉｔ／ｓ，而ＷＤＭ是让一根光纤同时传输几路或几十路不同波长的光信号，就可达到Ｔｂｉｔ／ｓ级的信号传输。 ＤＷＤＭ网络已得到了广泛的应用。它满足了提升通信容量的需要，但它本身…     

WDM光传送网的保护策略

在传送网中,采用ＷＤＭ、ＳＤＨ、ＡＴＭ技术已经导致更多的业务量集中在较少的网络元素中传输。例如,传输２．５Ｇｂ／ｓ ＳＤＨ信号的４０个波长ＷＤＭ系统的一个故障就能影响１,２００万电话呼叫,因此,这样的网络中的故障的影响是非常大的。 网络的生存能力就是把受故障影响的业务恢复的一种能力。在设计通信网络时,网络的生存能力是至关重要的。 从网络的管理观点出发,在构建抗故障ＷＤＭ光传送网时,建立网络保护策略和ＯＡ＆Ｍ（操作监控与管理）技术是至关重要的。 光传输网 数据流量的急剧增长导致通信业务量的指数增长。为…     

Virtual Source Based Multicast Routing in WDM Optical Networks

Wavelength-division multiplexed (WDM) networks using wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. Multicasting is the ability to transmit information from a single source node to multiple destination nodes and is becoming an important requirement in high-speed networks. As WDM technology matures and multicast applications become increasingly popular, supporting multicast routing at the WDM layer becomes an important and yet a challenging topic. This paper concerns with the problem of optical multicast routing in WDM networks. A few nodes in the network may have wavelength conversion and/or splitting capabilities. In this paper, a new multicast tree construction algorithm is proposed. This algorithm is based on a concept called virtual source. A virtual source is a node having both the splitting and wavelength conversion capabilities. By exploiting the presence of virtual source nodes, the proposed algorithm achieves improved performance. To further improve the performance, the algorithm assigns priorities to nodes based on their capabilities. The effectiveness of the proposed algorithm is verified through extensive simulation experiments.     

Operation of WDM networks with different wavelength conversioncapabilities

We study the impact of wavelength conversion capability on wavelength routing WDM networks with fixed shortest-path routing. We propose a method for implementing wavelength routing in a WDM network with partial wavelength conversion capability. Simulation results show that such partial wavelength conversion networks provide a performance in between that of wavelength continuous networks and those with full conversion capability. In addition, it can be seen that only limited wavelength conversion capability is enough to provide a performance close to that of a network with full conversion. Analytical and simulation bounding results for the full and no conversion cases have also been provided     

Wavelength conversion technologies for WDM network applications

WDM networks make a very effective utilization of the fiber bandwidth and offer flexible interconnections based on wavelength routing. In high capacity, dynamic WDM networks, blocking due to wavelength contention can he reduced by wavelength conversion. Wavelength conversion addresses a number of key issues in WDM networks including transparency, interoperability, and network capacity. Strictly transparent networks offer seamless interconnections with full reconfigurability and interoperability. Wavelength conversion may be the first obstacle in realizing a transparent WDM network. Among numerous wavelength conversion techniques reported to date, only a few techniques offer strict transparency. Optoelectronic conversion (O/E-E/O) techniques achieve limited transparency, yet their mature technologies allow deployment in the near future. The majority of all-optical wavelength conversion techniques also offer limited transparency but they have a potential advantage over the optoelectronic counterpart in realizing lower packaging costs and crosstalk when multiple wavelength array configurations are considered. Wavelength conversion by difference-frequency generation offers a full range of transparency while adding no excess noise to the signal. Recent experiments showed promising results including a spectral inversion and a 90 nm conversion bandwidth. This paper reviews various wavelength conversion techniques, discusses the advantages and shortcomings of each technique, and addresses their implications for transparent networks     

波分复用光网中的一种新型波长分配算法

目前网络承载业务的趋势是以IP为中心的数据业务,从而促进了以WDM光网络向高速和宽带多波长的应用和普及,为了进一步提高网络的性能并提高资源利用率,出现了光网络控制面技术.路由选择与波长分配问题是WDM光传输网络控制面中非常重要的问题之一.目前实际应用最广泛的波长分配算法是First-Fir(FF)算法.本文基于FF算法,研究动态业务下波分复用光网络在固定选路下的波长分配问题,提出了一种新的波长分配启发式算法——Joint First Fit.计算机仿真试验表明,与常用的FF算法相比,该算法显著的降低了网络呼叫阻塞率,有利于提高网络资源的利用率.     

Multicast connection capacity of WDM switching networks with limited wavelength conversion

Currently, many bandwidth-intensive applications require multicast services for efficiency purposes. In particular, as wavelength division multiplexing (WDM) technique emerges as a promising solution to meet the rapidly growing demands on bandwidth in present communication networks, supporting multicast at the WDM layer becomes an important yet challenging issue. In this paper, we introduce a systematic approach to analyzing the multicast connection capacity of WDM switching networks with limited wavelength conversion. We focus on the practical all-optical limited wavelength conversion with a small conversion degree d (e.g., d=2 or 3), where an incoming wavelength can be switched to one of the d outgoing wavelengths. We then compare the multicast performance of the network with limited wavelength conversion to that of no wavelength conversion and full wavelength conversion. Our results demonstrate that limited wavelength conversion with small conversion degrees provides a considerable fraction of the performance improvement obtained by full wavelength conversion over no wavelength conversion. We also present an economical multistage switching architecture for limited wavelength conversion. Our results indicate that the multistage switching architecture along with limited wavelength conversion of small degrees is a cost-effective design for WDM multicast switching networks.     

Nonblocking WDM switching networks with full and limited wavelength conversion

In previous years, with the rapid exhaustion of the capacity in wide area networks led by Internet and multimedia applications, demand for high bandwidth has been growing at a very fast pace. Wavelength-division multiplexing (WDM) is a promising technique for utilizing the huge available bandwidth in optical fibers. We consider efficient designs of nonblocking WDM permutation switching networks. Such designs require nontrivial extensions from the existing designs of electronic switching networks. We first propose several permutation models in WDM switching networks ranging from no wavelength conversion, to limited wavelength conversion, to full wavelength conversion, and analyze the network performance in terms of the permutation capacity and network cost, such as the number of optical cross-connect elements and the number of wavelength converters required for each model. We then give two methods for constructing nonblocking multistage WDM switching networks to reduce the network cost.     

全光归零(RZ)到非归零(NRZ)码型转换技术研究进展

随着多媒体网络服务业务类型的不断出现,人们对因特网带宽需求日益增长,未来的超高速大容量光子网络很可能是波分复用与时分复用相结合的智能网络。全光归零(RZ)到非归零(NRZ)的码型转换技术,是构建这种网络的关键技术之一,它能避免电子学器件的速率瓶颈,将时分复用(OTDM)与波分复用(WDM)有机结合,在光域内实现不同调制格式的数据在网络的不同部分之间自由传输,已经引起了越来越多人们的兴趣。介绍了当前全光归零到非归零码型转换技术的最新研究进展,分析了其工作原理,优缺点及性能参数,指出了目前存在的技术难点问题,最后对其发展前景进行了展望。     

Wavelength converters in dynamically-reconfigurable WDM networks

In simple wavelength-division multiplexed (WDM) networks, a connection must be established along a route using a common wavelength on all of the links along the route. This constraint may be removed by the introduction of wavelength converters, which are devices which take the data modulated on an input wavelength and transfer it to a different output wavelength. Wavelength converters thus improve network blocking performance. However, the introduction of wavelength converters into WDM cross-connects increases the hardware cost and complexity. Thus, it is important to establish precisely what advantages wavelength converters offer WDM networks. There has been considerable interest in the literature in the performance improvements offered by the introduction of wavelength converters into dynamically-reconfigurable WDM networks. This article provides a review of the conclusions drawn from these investigations. The performance improvements offered by wavelength converters depend on a number of factors, including network topology and size, the number of wavelengths, and the routing and wavelength assignment algorithms used. We discuss these factors here. However, it has been shown that wavelength converters offer only modest performance improvements in many networks. We also consider networks with limited wavelength conversion, in which the set of allowable conversions at a network node is constrained by having limited numbers of wavelength converters, or by using non-ideal wavelength converters. Limited wavelength conversion has been shown to provide performance which is often close to that achieved with ideal wavelength conversion in networks with tunable transmitters and receivers.     

Multiwavelength optical networks with limited wavelength conversion

This paper proposes optical wavelength division multiplexed (WDM) networks with limited wavelength conversion that can efficiently support lightpaths (connections) between nodes. Each lightpath follows a route in a network and must be assigned a channel on each link along the route. The load λ_max of a set of lightpaths is the maximum over all links of the number of lightpaths that use the link. At least λ_max wavelengths will be needed to assign channels to the lightpaths. If the network has full wavelength conversion capabilities, then λ_max wavelengths are sufficient to perform the channel assignment. Ring networks with fixed wavelength conversion capability within the nodes are proposed that can support all lightpath sets with load λ_max at most W-1, where W is the number of wavelengths in each link. Ring networks with a small additional amount of wavelength conversion capability within the nodes are also proposed that allow the support of any set of lightpaths with load λ_max at most W. A star network is also proposed with fixed wavelength conversion capability at its hub node that can support all lightpath sets with load λ_max at most W. These results are extended to tree networks and networks with arbitrary topologies. This provides evidence that significant improvements in traffic-carrying capacity can be obtained in WDM networks by providing very limited wavelength conversion capability within the network