静态P-Cycles双链路故障保护策略的研究

p-Cycles应用在WDM格网中可以得到高的容量利用平和快速保护倒换时间，本文给出了一种格网生存性有关客量问题的研究方法，即孤立节点分析法，提出了p-Cycles在双链路故障情况下的保护策略．并建立了以保护容量需求作为优化目标的p-Cycles优化设计模型。     

抗毁WDM光网络中SRLG约束下p-Cycles配置算法

基于共享风险链路组(SRLG,shared risk link group)和P圈(P-Cycles,pre-configured cycles)的概念,研究了SRLG约束下p-Cycles的构造问题,引入SRLG完全分离p-Cycles的概念,基于SRLG的简单p-Cycles构造算法和获得更多p-Cycles的SRLG约束下的圈扩展算法提出的SRLG约束下的p-Cycles配置算法(SCAA),实现在光网络中优化配置SRLG完全分离的p-Cycles。通过计算机仿真表明,SCAA最小容量配置方案可以预留更少的网络资源,而SCAA优化容量配置方案可以实现p-Cycles快速配置容量,SCAA算法可以保障配置SRLG分离p-Cycles的高保护效能,使网络具备单SRLG故障恢复能力。     

基于两级业务交叉连接节点的光网络的生存性问题

本文研究了由两级业务交叉连接节点构成的光网络的保护设计问题,并创建了保护容量规划模型.模型的仿真结果表明,模型的优化目标和网络容量的分配策略对网络的保护性能有重要影响.     

基于共享通道保护的容量优化设计算法

对于给定业务,宽带传输网所需的总传输容量是影响网络成本的重要因素。提出了一种基于共享通道保护的容量优化设计算法MSC-JOCP,通过动态调整链路权值的方法,在“负载均衡”的前提下优化地选择业务工作路由和保护路由,同时保证不同业务的保护路由之间可以最大程度地共享备份资源。仿真结果表明,算法能有效地提高网络的资源利用率,降低网络总传输容量。     

工作容量约束下光网络p圈空闲容量分配算法

基于网状光网络p圈保护算法，研究了常见简单p圈和空闲容量分配的常见问题，介绍了光网络中局部图概念，针对如何在光网络拓扑中优化配置p圈，提出获得更多性能优良圈的局部图扩展算法和工作容量约束下启发式p圈空闲容量分配算法。通过计算机仿真表明，该算法在考虑工作容量的分布情况下，既实现快速空闲容量配置又保证保护效能高。该算法性能优于基于空闲容量的启发式p圈分配算法，适合在给定空闲容量分布情况下的网状光网络高保护效能p圈的配置。     

光传送网环覆盖保护策略研究

生存性是光传送网络中亟待解决的问题.文章基于环网的优良保护倒换能力提出了环覆盖保护策略,给出了选择环覆盖的控制流程,建立了以保护容量需求作为优化目标的环覆盖优化设计模型.     

基于改进的粒子群算法的ASON保护容量问题求解

针对求解ASON网络保护容量的NP完全非线性组合优化问题,提出了基于改进粒子群(PSO)搜索寻优算法.与线性规划寻优方法相比,该算法在可行解搜索空间及计算量上大大降低,为算法在工程上的实现提供了可行性.同时跟其它的进化计算方法(如免疫、遗传、蚂蚁等)相比,PSO简单、容易实现、不需要调整许多参数.仿真实验结果表明该算法计算效率大大超越整数线性规划(ILP),同时也略优于遗传算法,更重要的是该算法结构简单、搜索效率高、能迅速地求出保护容量优化问题的全局近似最优解.     

一种利用理想拓扑的保护容量分配算法

对于通常的网状网,如何设计最小的保护容量来保证快速恢复是一个富有挑战性的问题。为了解决如何分配更少的保护容量的问题,该文提出了一些理想的拓扑结构,研究了支撑树算法。在这两者的基础上针对一条链路出现故障的问题给出了利用理想拓扑的保护容量分配算法。仿真结果说明该算法能预留比支撑树算法少得多的保护容量。     

激光陀螺旋转调制惯导高纬度地区导航算法分析

针对当地水平地理坐标系在高纬度地区失效的问题，在格网坐标系下对惯性导航算法重新进行了编排，并分析了格网坐标系表示下的惯导误差方程。结合激光陀螺旋转调制惯导的特点，设计仿真实验和实际实验对格网坐标系下的惯导算法有效性进行验证。实验结果表明，以格网坐标系作为导航坐标系，能够解决高纬度地区经线汇聚带来的计算问题。     

浅析CDMA2000容量优化

CDMA系统是自干扰、容量受限的系统。在CDMA2000系统中,空中接口的容量与业务的Eb/Io、增益处理、其他小区的干扰、基站发射功率和信道码的数量相关,也就是说,CDMA的容量是软容量。容量、网络性能、质量永远是相互矛盾的关系。只有对网络容量进行有效优化,才能更好地平衡三者关系。文章介绍CDMA2000容量优化的重要性,说明容量优化的原理及影响容量的因素,分析容量优化可能采用的方法,最后进行评估。     

基于P环的恢复机制在WDM网状网中的应用

目前波分复用(WDM)网状网中所采用的恢复机制的恢复速度较慢,不能满足某些业务的需求。利用空闲容量建立的p环(pmcmtfigured cycles)具有环形网的速度和网状网的容量效率。它的操作方法简单,使用灵活,可以应用于WDM网和IP网等不同的网络。本文详细介绍了p环的基本原理、构造过程及优化方法或讨论了多故障的情形,并对一些新的研究方向作了评述,可供网络设计者参考。     

Theoretical underpinnings for the efficiency of restorable networksusing preconfigured cycles (“p-cycles”)

Previous work on restorable networks has shown experimentally that one can support 100% restoration with an optimized set of closed cycles of spare capacity while requiring little or no increase in spare capacity relative to a span-restorable mesh network. This is important and unexpected because it implies that future restoration schemes could be as capacity efficient as a mesh network, while being as fast as ring-based networks because there is no real-time work at any nodes other than the two failure nodes. This paper complements the prior work by giving a greater theoretical basis and insight to support the prior results. We are able to show in a bounding-type of argument that the proposed protection cycles (“p-cycles”) have as high a restoration efficiency as it is possible to expect for any type of preconfigured pattern, and are categorically superior to preconfigured linear segments or trees. We are also able to show that the capacity efficiency of a fully preconfigured p-cycle network has the same well-known lower bound as that of a span restorable mesh network which is cross-connected on-demand. These results provide a theoretical underpinning for the efficiency of p-cycles and confirmation of the experimental observations     

A framework for service-guaranteed shared protection in WDM meshnetworks

In this article a framework for end-to-end service-guaranteed shared protection in dynamic wavelength division multiplexing (WDM) mesh networks, called short leap shared protection (SLSP), is introduced. The idea of SLSP is to divide each working path into several overlapped protection domains, each of which contains a working and protection path pair. In addition to a guaranteed restoration service, SLSP is designed to satisfy the future requirements of wavelength-routed optical mesh networks in scalability, class of service, and capacity efficiency. Tutorial-like discussions are given in the architecture design and signaling mechanisms for implementing the SLSP framework in a dynamic network environment with examples and illustrations. To show that SLSP can improve capacity efficiency, simulations are conducted using four networks (22-, 30-, 79-, 100-node) for a comparative study between ordinary shared protection schemes and SLSP     

Restoration of all-optical mesh networks with path-based flooding

The exponential growth of data traffic has led to substantial deployment of wavelength-division multiplexing networks. Reliability becomes increasingly important as the number of critical applications that depend on proper operation of these networks grows. Protection against failures of links or nodes can be achieved using a wide variety of approaches, which offer tradeoffs in terms of speed of recovery, cost of equipment, protection capacity, and management overhead. Optically transparent networks provide several advantages over optically opaque networks for supporting the growing communication demands, but suffer from several drawbacks that make direct application of the most capacity-efficient protection schemes difficult. In this paper, we introduce a flooding-based recovery scheme for optically transparent networks that provides 100% recovery from all single link and node failures in a capacity-efficient manner. In essence, this scheme applies the notion of active flooding of backup traffic introduced by generalized loopback to the problem of path protection. Our recovery scheme can achieve fast restoration (comparable to rings) with little data loss by using backup traffic flooding without the overhead of signaling and setup of intermediate cross-connects along the recovery path. We present simulation results for online provisioning of lightpaths with uniformly distributed traffic demands over optically transparent networks using our restoration scheme. The results show that the scheme offers an interesting tradeoff between capacity cost and recovery speed for all-optical networks. For five representative networks, the approach limits data loss to about 20 ms while using 14% less capacity relative to dedicated (1:1) mesh protection. Shared mesh protection (path protection) with a wavelength continuity constraint uses 19% less capacity with roughly 90 ms of data loss.     

Simple Pre-Provisioning Scheme to Enable Fast Restoration

Supporting fast restoration for general mesh topologies with minimal network over-build is a technically challenging problem. Traditionally, ring-based SONET networks have offered close to 50 ms restoration at the cost of requiring 100% over-build. Recently, fast (local) reroute has gained momentum in the context of MPLS networks. Fast reroute, when combined with pre-provisioning of protection capacities and bypass tunnels, enables faster restoration times in mesh networks. Pre-provisioning has the additional advantage of greatly simplifying network routing and signaling. Thus, even for protected connections, online routing can now be oblivious to the offered protection, and may only involve single shortest path computations. In this paper, we are interested in the problem of reserving the least amount of the network capacity for protection, while guaranteeing fast (local) reroute-based restoration for all the supported connections. We show that the problem is NP-complete, and we present efficient approximation algorithms for the problem. The solution output by our algorithms is guaranteed to use at most twice the protection capacity, compared to any optimal solution. These guarantees are provided even when the protection is for multiple link failures. In addition, the total amount of protection capacity reserved by these algorithms is just a small fraction of the amount reserved by existing ring-based schemes (e.g., SONET), especially on dense networks. The presented algorithms are computationally efficient, and can even be implemented on the network elements. Our simulation, on some standard core networks, show that our algorithms work well in practice as well     

Understanding interference and carrier sensing in wireless mesh networks [Accepted from Open Call]

Wireless mesh networks aim to provide high-speed Internet service without costly network infrastructure deployment and maintenance. The main obstacle in achieving high-capacity wireless mesh networks is interference between the mesh links. In this article, we analyze the carrier sensing and interference relations between two wireless links and measure the impact of these relations on link capacity on an indoor 802.11a mesh network testbed. We show that asymmetric carrier sensing and/or interference relations commonly exist in wireless mesh networks, and we study their impact on the link capacity and fair-channel access. In addition, we investigate the effect of traffic rate on link capacity in the presence of interference.     

Multicast protection scheme based on Hamiltonian cycle in fault-tolerant optical mesh networks

The increase of multimedia service requirements results in the growing popularity of the multicast in Wavelength-Division Multiplexing (WDM) optical mesh networks. Multicast fault tolerance in WDM optical mesh networks is an important issue because failures caused by the traffic carried in WDM optical mesh networks may lead to huge data loss. Previous works have proposed multicast protection algorithms to address the single-fiber link failure dominant in current optical mesh networks. However, these existing algorithms are all mainly based on path protection or segment protection, which may lead to long restoration times and complicated protection switching procedures. This paper therefore proposes a new heuristic algorithm, called Enhanced Multicast Hamiltonian Cycle Protection (EMHCP), in which all working light-trees of multicast demands can be protected by a Hamiltonian cycle in the network. For each multicast demand, EMHCP computes a least-cost light-tree based on the presented link-cost function that considers load balancing and proper straddling link selection so that backup wavelengths on the Hamiltonian cycle can be reduced. Simulation results show that EMHCP can obtain significant performance improvement compared with the conventional algorithm.