光子网格技术及应用

光子网格是近年来出现的一个全新的、跨学科的研究领域,它具有广阔的应用领域及市场前景.本文首先介绍了光子网格产生的背景,然后分析了光子网格研究的关键问题及进展情况,最后给出了一些应用实例.     

基于距离自适应和有效共享路径感知的光疏导方法

针对灵活网格光网络中如何节约转发器与频谱资源的问题,该文研究了多点到多点组播业务的光路环路由机制,提出一种基于距离自适应和有效共享路径感知的光疏导方法。通过设计一种基于距离自适应的预处理机制,该疏导方法能根据业务成员节点的分布特点和距离自适应准则灵活地为业务构建光路环;在路由与频谱分配阶段,该疏导方法通过构造一个面向光疏导的业务决策矩阵和一个优先调度向量,将业务疏导到与当前业务具有有效共享路径最多的已路由业务上,并优先分配所需的频谱空间以提高光疏导的成功率,实现节约转发器与频谱资源的目的。仿真结果表明,该文提出的光疏导方法可以有效地减少业务消耗的转发器数目和子载波数目。     

ASON中共享路径保护机制的实现方法

研究了自动交换光网络(ASON)中,保护资源可部分共享的共享路径保护机制(Shared Path Protection,SPP)如何实现的问题.设计了该机制在符合波长连续性限制条件的WDM光网络中的路由计算算法及在ASON上实现该机制的信令流程.在ASON实验平台上实现了该机制.     

按需路由协议研究与应用

介绍了自组网的有关特性和按需路由的必要性,分析了按需路由的协议原理并对DSR协议进行了实现,最后通过测试验证,在低宽带网络中保证了路由的快速获取及很好的用户体验。     

宽带接入网支持按需带宽业务及动态QoS的研究

宽带网络所承载的业务正从以传统互联网业务为主逐步向多业务承载方向发展,宽带接入网络必须实施网络转型以适应市场需求的变化和业务发展的需求。本文对按需带宽分配（BoD）业务以及BoD业务在宽带接入中的QoS需求进行了分析和研究,并进一步提出了在接入网内实施动态QoS々策略。     

光网络与光子集成的发展(上)

本文从高速率大容量信息网络体系的发展需求出发,指出光纤网络体系是未来光通信的主流发展方向,光子技术将在网络体系中成为主体技术,发挥重大的作用.文中描述了光纤网络体系的基本功能构架:即信息的超大容量传输,灵活的上下载路分插复用,快速的交换共享和高效经济的路由选择.光子集成是实现上述功能构架的关键硬件,它包括高速响应的集成激光器、波导光栅阵列密集波分复用器、可调谐窄带响应集成光电探测器、路由选择的波长变换器以及快速响应光开关矩阵等.重点将对上述支撑高速率、大容量光纤网络体系的集成光子器件的发展作出较深入的评述讨论.     

光网络与光子集成的发展(上)

本文从高速率大容量信息网络体系的发展需求出发,指出光纤网络体系是未来光通信的主流发展方向,光子技术将在网络体系中成为主体技术,发挥重大的作用。文中描述了光纤网络体系的基本功能构架：即信息的超大容量传输,灵活的上下载路分插复用,快速的交换共享和高效经济的路由选择。光子集成是实现上述功能构架的关键硬件,它包括高速响应的集成激光器、波导光栅阵列密集波分复用器、可调谐窄带响应集成光电探测器、路由选择的波长变换器以及快速响应光开关矩阵等。重点将对上述支撑高速率、大容量光纤网络体系的集成光子器件的发展作出较深入的评述讨论。     

业务驱动的光子网格关键技术研究

通过对光子网格资源管理新机制、光子网格中间件和光子网格用户网络接口等关键技术的研究，建立业务驱动的光资源动态调度方法，给出大块数据传输及视频点播（VOD）服务在可控光路与基于OBS的网格（Grid over OBS）模式下的业务应用模式。理论与实验证明业务驱动的光子网格关键技术的实现，使得光子网格能很好地为密集数据业务服务。     

移动Adhoc网络中按需路由协议的安全性改进方案

在移动Adhoc网络中,安全性是保证其可用性的一个重要方面.文章提出了一种针对按需路由协议的安全性改进方案,这种方案采用了对邻居节点的身份即时认证、对远端节点按需认证、匿名寻找路由,逐跳加密传输的机制,能够有效地阻止恶意节点对网络的窃听、篡改等攻击,确保网络路由信息的安全.     

MANET中一种新的基于节点位置的按需路由算法

移动Ad hoc网络(MANET)是一种由无线移动主机/节点组成的动态自治网络.在MANET中进行有带宽保证的按需路由选择具有重要意义.本文提出一种新的按需路由算法LABGR(Location Aided Bandwidth Guaranteed Routing).LABGR以节点当前位置信息为基础,在路由选择过程中把路径稳定性和节点能量受限问题结合起来,采用受限扩散路由方法,利用多种机制避免在全网中进行扩散,限制路由请求过程中被影响的节点数目,有效提高了路由请求效率并且保证了链路带宽.本文还对LABGR算法特性进行了深入分析.     

Parallel and multi-wavelength downloading in optical grid networks

In optical grid networks, data files for job execution are replicated at multiple sites in order to distribute loads and achieve high performance computing. Those replicas are downloaded in parallel in order to reduce downloading time. Furthermore, each replica is downloaded with multiple wavelengths. Although parallel and multi-wavelength downloading reduce downloading time, they raise blocking probability of file downloading. This is because they use a lot of wavelength resources and thus often generate bottleneck links. To resolve this problem, this paper proposes a parallel and multi-wavelength downloading scheme for optical grid networks. The proposed scheme provides replica selection, route selection, and wavelength selection for parallel and multi-wavelength downloading. In the proposed scheme, clients dynamically select combinations of a replica, a route, and a wavelength in such a way that they suppress the generation of bottleneck links. Through simulation experiments, we show that the proposed scheme efficiently improves blocking probability of parallel and multi-wavelength downloading.     

Parallel transmission of images through single optical fibers

The characteristics and limits of parallel transmission of two-dimensional imagery through single optical fibers are reviewed, and methods for overcoming the inherent smearing that occurs at the output are discussed. These solutions include: a) control of the fiber's refractive index profile; b) incorporation of complex filters; and c) encoding the information at the input and decoding the output after transmission.     

Dynamic lightpath provisioning in optical WDM mesh networks with asymmetric nodes

The wavelength selective switch-based reconfigurable optical add/drop multiplexers is a promising switching equipment for future reconfigurable wavelength-division multiplexing (WDM) mesh networks. However, its asymmetric switching property complicates the optimal routing and wavelength assignment problem. In an asymmetric switching scenario, using the classic Dijkstra’s algorithm can lead to invalid paths traversing unconnected ports of an asymmetric node. To solve this problem, we propose both link-state (LS) and distance vector (DV) schemes for dynamic lightpath provisioning in optical WDM mesh networks with asymmetric nodes. The proposed LS schemes include the asymmetric switching-aware (ASA) Dijkstra’s algorithm, the $K$ -shortest path-based algorithm, and the entire path searching (EPS) algorithm. Simulation results show that the ASA-Dijkstra’s algorithm will bring notable improvement of the blocking performance with low computational complexity, while the EPS algorithm has much higher complexity and is not suitable to be employed in large-scale networks. On the other hand, our proposed DV solution, i.e., the information diffusion-based routing (IDBR), can achieve the lowest blocking probability with the lowest computational complexity. Moreover, IDBR does not require the distribution of local asymmetric switching information like the LS schemes, thus having a high level of topology confidentiality.     

A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability. We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance. The objective is to maximize the number of established lightpaths for a given number of wavelengths. Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally. In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic. BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems. We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem. Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms. In addition, we compare the results of the BCO–RWA–SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands.     

On-demand transmission of 3D models over lossy networks

Three-dimensional (3D) meshes are used intensively in distributed graphics applications where model data are transmitted on demand to users’ terminals and rendered for interactive manipulation. For real-time rendering and high-resolution visualization, the transmission system should adapt to both data properties and transport link characteristics while providing scalability to accommodate terminals with disparate rendering capabilities. This paper presents a transmission system using hybrid unequal-error-protection and selective-retransmission for 3D meshes which are encoded with multi-resolutions. Based on the distortion-rate performance of the 3D data, the end-to-end channel statistics and the network parameters, transmission policies that maximize the service quality for a client-specific constraint is determined with linear computation complexity. A TCP-friendly protocol is utilized to further provide performance stability over time as well as bandwidth fairness for parallel flows in the network. Simulation results show the efficacy of the proposed transmission system in reducing transmission latency and providing smooth performance for interactive applications. For example, for a fixed rendering quality, the proposed system achieves 20–30% reduction in transmission latency compared to the system based on 3TP, which is a recently presented 3D application protocol using hybrid TCP and UDP.     

Analysis of blocking probability for distributed lightpath establishment in WDM optical networks

In this paper, we analyze the blocking probability of distributed lightpath establishment in wavelength-routed WDM networks by studying the two basic methods: destination-initiated reservation (DIR) and source-initiated reservation (SIR). We discuss three basic types of connection blocking: 1) blocking due to insufficient network capacity; 2) blocking due to outdated information; and 3) blocking due to over-reservation. It is shown that the proposed models are highly accurate for both the DIR and the SIR methods, in both the regular and irregular network topologies, under the whole range of traffic loads.     

Sliding scheduled lightpath provisioning by mixed partition coloring in WDM optical networks

In WDM optical networks, lightpath provisioning for static, incremental and dynamic traffic model has been widely investigated. However, Internet connectivity services are increasingly showing a new kind of traffic type in the context of optical networks, i.e., sliding scheduled traffic, which does not have a rigid deadline and allows flexible sliding within a large time window. This new traffic type offers opportunity of more efficiently utilizing network resources to accommodate more traffic, and poses new challenges of exploiting the flexibility of scheduling time. In this paper, we formulate the static sliding scheduled lightpath demand (SSLD) provisioning problem as a mixed partition coloring model in which routing and wavelength assignment are conducted simultaneously in compliance with the allowed time window of each request. Then, we propose a novel one-step heuristic algorithm named as maximum conflict degree first conflict reducing (MCDF-CR) to solve the SSLD provisioning problem based on mixed partition coloring model. Simulation results show that our approach can improve wavelengths utilization compared to previous heuristics.     

Post‐Disaster least loaded lightpath routing in elastic optical networks

Disaster events directly affect the physical topology of core networks and may lead to simultaneous failure of multiple lightpaths leading to massive service outages for network operators. To recover from such a failure scenario, the existing routing algorithms running on network nodes (routers or switches) typically attempt to reestablish the connections over new routes with shortest distances and hop count approach. However, this approach may result in congestion on some links, while other links may have the unutilized capacity. Hence, intelligent lightpath computing techniques are required to efficiently route network traffic over the new routes by considering traffic load of each link in addition to distance and hop count to minimize network congestion. In this paper, we have proposed a capacity‐constrained maximally spatial disjoint lightpath algorithm to tackle the provisioning and restoration of disrupted lightpaths in a postdisaster scenario in the context of elastic optical networking. This algorithm computes an alternate least loaded lightpath for disrupted primary lightpath using capacity‐constrained shortest lightpath. Alternate lightpath selection is based on a criteria parameter for a lightpath to be least loaded and constrained by either the length or the spatial distance between primary and alternate lightpaths. The spatial distance between lightpaths enables to reestablish the disrupted connection request away from disaster proximity. The performance of the proposed algorithm is evaluated through simulation for several parameters like blocking probability, network utilization, connection success rates, and minimum spatial distance.     

Distributed optical control plane for dynamic lightpath establishment in translucent optical networks based on reachability graph

In transparent optical networks, physical layer impairments (PLIs) incurred by non-ideal optical transmission media accumulate along an optical path, and the overall effect determines the optical feasibility of the lightpaths. In addition, transparent optical networks suffer from inefficient wavelength utilization, as a connection request may be rejected because of non-availability of a common wavelength on all the links along the chosen route. To increase optical reach, resource utilization, and average call acceptance ratio (and hence revenues), network operators are resort to translucent optical networks. In these networks a limited number of regenerators are placed at a selected set of nodes. In this scenario development of an optical control plane which is aware of PLIs, location and number of regenerators, is of paramount importance for on-demand lightpath provisioning. In this paper, we propose a novel approach of constructing a reachability graph of the physical network considering PLIs and regenerators. If there is no transparent path in the physical network, we route the connections with multiple transparent segments on the reachability graph. We propose efficient mechanisms and corresponding GMPLS protocol extensions for impairment and regenerator aware routing and wavelength assignment (IRA-RWA) in translucent optical networks. The simulation results suggest that our proposed approach together with LSP stitching signaling mechanism is feasible to implement and close to deployment.     

A hierarchical extension to RSVP-TE for fast lightpath setup in dynamic optical networks

A dynamic optical network with a fast resource allocation ability is proposed to satisfy the increasing requirement of the fast developing services. The lightpath setup delay of the traditional serial signaling distribution method used by RSVP-TE and CR-LDP increases linearly with increasing scale of the network. When the network size becomes too large, the signaling delay may cause problems to real-time services and fast recovery. So, we propose a combined hierarchical signaling distribution (CHSD) method for fast lightpath setup and an extended RSVP-TE to support a hierarchical signaling distribution process. The simulation and theoretical analysis show that the lightpath setup delay by CHSD is reduced from O(N), which is the delay of the traditional serial distribution method, to in the best condition. The delay is also related to the hierarchical structure of the network and when the scale of the routing areas (RA) takes a uniform distribution and the RA number equals to , a minimum distribution delay is achieved. Thereafter, we extend RSVP-TE to support this hierarchical distribution method. By the simulation result, the extension is proved to be feasible.