Shared p-cycles design for dual link failure restorability in optical WDM networks

Pre-configured cycles (p-cycles) can attain high capacity efficiency and fast protection switching times in wavelength division multiplexing (WDM) networks.This article proposes the weighted straddling link algorithm (WSLA) for generating a subset of all cycles that can guarantee 100% restorability in case of dual link failure, and give an integer linear programming (ILP) formulation that solves the shared p-cycles design problem minimizing the total spare capacities.Numerical result shows that our method can achieve 100% dual link failure restorability with acceptable spare capacity.The larger standard deviation of demand set and the larger node degree network, the better the shared p-cycles scheme performs.     

A study of the backup reprovisioning problem for FIPP p-cycles on WDM networks

As networks grow in size and complexity, both the probability and the impact of failures increase. The pre-allocated backup bandwidth cannot provide 100% protection guarantee when multiple failures occur in a network. In this article, we focus on how to recover the protecting capabilities of FIPP (Failure-independent path-protecting) p-cycles against the subsequent links failure on WDM networks, after recovering the working paths affected by the failure of link. Two recovering policies are designed to recover the protecting capabilities of the FIPP p-cycles if possible, unless there is no sufficient network resource. They are Cycle Recovery Policy and Path Recovery Policy. In addition, a Cycle Adjust algorithm is proposed and used to recover the affected cycles. The simulation results of the proposed methods are also given.     

The backup reprovisioning problem of FIPP p-cycles for node failure on survivable WDM networks

Protection techniques for optical networks mainly rely on pre-allocated backup bandwidth, which may not be able to provide full protection guarantee when multiple failures occur in a network. After recovering from the previous failure, if failure occurs again, unprotected or vulnerable lightpaths cannot be recovered. In this paper, the minimal backup reprovisioning (MBR) problem is studied, in which the failure-independent path protecting p-cycles (FIPP p-cycles) scheme is considered for single-node failure on WDM networks. After recovering the affected lightpaths from a node failure, the goal of the MBR is to re-arrange the protecting and available resources such that working paths can be protected against next node failure if possible. An algorithm is designed to recover the protecting capabilities of the FIPP p-cycles, unless there is no sufficient network resource. The simulation results of the proposed method are also given.     

非割边链路故障对网络流量的影响分析

在骨干网络中,几乎每天都会发生链路故障,链路故障会导致流量损失或转移.应用概率论方法给出了流量损失时间及转移时间与相应的协议配置及非割边链路故障特性的量化关系.研究结果可用来指导协议配置以减少故障对流量的影响.     

Network restoration under dual failures using path-protecting preconfigured cycles

This paper presents a design algorithm for networks with a restoration mechanism that provides end-to-end path protection to a set of demands with specified working routes, where demands must survive one or two failures in optical networks and these failures may occur almost instantaneously. Each of the demands protected from two failures is assigned two restoration routes and restoration wavelengths on a cycle. A demand protected from a single failure is assigned one restoration route and restoration wavelengths on a cycle. These assignments are preconfigured so that switching and wavelength conversions are not needed at intermediate nodes of restoration routes. Splitting of demand across multiple restoration routes upon a failure occurrence is not allowed. The algorithm generates a large number of candidate Path-Protecting Preconfigured Cycles (PP-PCs). A candidate cycle may provide protection to a mix of demands requiring different protection levels, where demands may share under certain conditions restoration wavelengths even if they are exposed to common failure scenarios and have overlapping restoration routes. A near-optimal set of preconfigured cycles is selected from among all candidates, attempting to minimize the total cost of restoration wavelengths while ensuring that each demand is assigned to a single preconfigured cycle. This is achieved by solving a set covering problem followed by deleting duplicate demand assignments and by resolving wavelength assignment conflicts.     

Reliable guaranteed variance filtering against sensor failures

This paper presents a solution to a reliable filtering problem with error variance specifications for both continuous- and discrete-time systems. The filtering error variance in the sensor failure cases is guaranteed to be less than a given upper bound while the performance in the nominal case is optimized. A convergent iterative algorithm based on linear matrix inequality (LMI) is given to obtain the solution. The algorithm solves the problem without introducing additional conservativeness, and it is shown to get better performance and be less conservative compared with traditional LMI approaches. A numerical example is given to show the advantages of our approach over existing techniques.     

一种静态P_Cycle双链路故障保护算法

首先分析了采用P_Cycle(P圈)为网络提供保护时会遇到的双链路故障发生情形,然后分析了在至少3边连通度格状网络中采用P圈偶对实现双链路故障保护的策略.提出了一种最优P圈偶对选取法则:最小等效长度和原则及一种圈共享方案,并在此基础上提出了一种采用P圈偶对实现双链路故障保护的启发式算法.最后,在COST239网络拓扑进行了仿真,仿真的结果验证了算法的有效性和可行性.     

Availability analysis under multiple link failures in WDM networks with shared-link connections

In optical Wavelength Division Multiplexing (WDM) networks, different protection schemes have been proposed in the literature, namely, dedicated protection and shared protection. Shared protection techniques significantly reduce the required spare capacity by providing the same level of availability as dedicated protection. However, current mission critical applications (which heavily depend on the availability of communication resources) require connection availability in the order of 99.999% or higher, which corresponds to a downtime of almost 5 min a year on the average. Therefore, in order to satisfy a connection serviceavailability requirement defined by the users Service Level Agreement in a cost-effective and resource-efficient way, network operators need a systematic mechanism to evaluate the network availability under multiple failure scenario to ensure that current network configuration can meet the required availability degree; otherwise, a network upgrade is required. Unfortunately, under multiple failure scenario, traditional availability analysis techniques based on reliability block diagrams are not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of network availability. In this paper, we propose an analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link failures. The analytical model is also verified using Monte Carlo simulation. The proposed model significantly contributes to the related areas by providing network operators with a quantitative tool to evaluate the system availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple link failures.     

An analysis of the congestion effects of link failures in wide areanetworks

The authors present the results of a study to determine the effects of link failures on the performance of a network in terms of the occurrence of congestion due to traffic restoration after a failure. The network studied is a virtual circuit based packet switched wide area network. A generic queueing framework is developed to study the effect of failures and the subsequent traffic restoration on network performance. In general, the congestion resulting after a failure is a transient phenomenon. Hence, a numerical methods based nonstationary queueing analysis is conducted in order to quantify the effects of failures in terms of the transient behavior of queue lengths and packet loss probabilities. A bounding relationship is developed whereby a network node can determine whether or not congestion will occur as the result of traffic restoration after a failure     

基于QR分解的强鲁棒性双彩色盲水印算法

提出了一种将彩色快速识别(QR)码作为水印嵌入彩色宿主图像的强鲁棒性盲水印算法。首先 对彩色宿主图像分通道进行离散小波 变换(DWT)和分块QR分解得到非重叠的酉矩阵,然后将QR码分通道置乱加密归一化后嵌入到 宿主图像对应通道 酉矩阵的系数差中。仿真实验结果表明,本算法在满足不可见性的同时具有较强的鲁棒性; 相比现有算法, 本算法不仅能够抵抗旋转和裁切攻击,在JPEG压缩和噪声滤波攻击方面的抵抗能力也有较 大提升;而且本算法属于盲水印技术,具有较大的实际应用价值。     

Contribution to future metropolitan access network planning considering link failures in photonic switched networks

Photonic switching for traffic optimization in Metropolitan Access Optical Networks using technologies of optical packet/burst switching (OPS/OBS) seems to be a future-proof solution considering high capacity and the highly variable traffic in these networks. Looking for this future, we propose a study based on the analyze of survivability of traffic unconsidering protection mechanism but considering mesh and ring efficient topologies with node architecture to OPS. The results are obtained through computer modeling and simulation. The main parameters analyzed are as follows: capacity, average number of hops, packet loss fraction, and link utilization for each topology. These parameters are adopted to evaluate the performance of each topology considering failures. Minimum electronic buffering is included at node ingress (client side) to avoid packet loss in the access to the optical layer: high throughput and low latency. It is also observed that optical buffering is not necessary for adequate network performance.     

基于DVI双链路的超大分辨率亮度校正系统设计

具备亮度校正功能的DVI-DVI处理器被应用到LED大屏幕显示,可以较好的解决工程上为了增加或升级亮度校正功能而更换显示控制系统的问题.但是DVI-DVI处理器的动态内存读取频率较低,不能发挥DVI双链路的数据传输性能.本文通过对动态内存中待读取的校正参量按照特定算法进行重组和压缩,将动态内存的等效读取频率从266MHz提高到330MHz,实现DVI双链路传输对超大分辨率的LED显示屏进行有效的亮度校正.     

An autonomous recovery mechanism against optical distribution network failures in EPON

Ethernet Passive Optical Network (EPON) is chosen for servicing diverse applications with higher bandwidth and Quality-of-Service (QoS), starting from Fiber-To-The-Home (FTTH), FTTB (business/building) and FTTO (office). Typically, a single OLT can provide services to both residential and business customers on the same Optical Line Terminal (OLT) port; thus, any failures in the system will cause a great loss for both network operators and customers. Network operators are looking for low-cost and high service availability mechanisms that focus on the failures that occur within the drop fiber section because the majority of faults are in this particular section. Therefore, in this paper, we propose an autonomous recovery mechanism that provides protection and recovery against Drop Distribution Fiber (DDF) link faults or transceiver failure at the ONU(s) in EPON systems. In the proposed mechanism, the ONU can automatically detect any signal anomalies in the physical layer or transceiver failure, switching the working line to the protection line and sending the critical event alarm to OLT via its neighbor. Each ONU has a protection line, which is connected to the nearest neighbor ONU, and therefore, when failure occurs, the ONU can still transmit and receive data via the neighbor ONU. Lastly, the Fault Dynamic Bandwidth Allocation for recovery mechanism is presented. Simulation results show that our proposed autonomous recovery mechanism is able to maintain the overall QoS performance in terms of mean packet delay, system throughput, packet loss and EF jitter.     

Robust phase-retrieval for quick whole-body SAR assessment using dual plane amplitude-only data

A robust phase-retrieval method with stable convergence and backpropagation properties for quick experimental whole body specific absorption rate (SAR) assessments is presented. A combination of a fast and coarse method and a more accurate gradient-based method is used to optimise the overall performance. To prevent the solution being trapped in a local minimum, several initial phase distributions are used. An accurate measurement procedure has been developed which reduces measurement time by roughly a factor of 2.5?4 at common mobile communication frequencies compared with a volume scan based procedure.     

Consecutive-2-of-n:F systems with node and link failures

It has always been assumed that nodes can fail but not links, although most examples given for the consecutive-k-out-of-n :F system show no reason for such an assumption. The system described not only allows links to fail, but allows both nodes and links to fail, with distinct probabilities. For the k=2 case, the authors set up recursive equations for system reliability, and give a closed-form solution. It is proved that for n large, the reliability is decreasing in n (with one exceptional case) and higher reliability should be provided to the nodes, and then to the longer links rather than to shorter links     

Fluctuations on OTS-Earth copolar link against diurnal and seasonal variations

Measurements on the copolar level of the 11.575 GHz OTS-Earth link have been analysed during the year 1981, using a 1 s sampling time. The variation of the fluctuations amplitude is evaluated as a function of the time of day and of the month of the year. It is compared to the number of attenuation events over the same period and against the same parameters. The statistic of the number of occurrences is calculated as a function of the amplitude of the events.     

以太网中双上行组网的弹性链路的设计与实现

为了在双上行组网的网络拓扑中避免形成环路,并进行冗余备份和快速倒换,传统方法是使用STP。但现有的STP的收敛速度慢,丢失流量较多,倒换时间较长,且协议复杂,会占用以太网交换机的大量资源。针对这些问题,提出了一种在双上行组网中实现主备链路冗余备份和快速倒换的弹性链路(RLink,Resilient Link)解决方案。对该方案的测试表明,能够实现预期的功能,并且占用资源少,易于操作。     

A hybrid protection strategy based on node-disjointness against double failures in optical mesh networks

As the size and the complexity of optical mesh networks are continuing to grow and the severe natural disasters are occurring more frequently in recent years, multiple failures (link failures or node failures) become increasing probable. Protection strategies against these failures generally provision backup paths for working paths based on link-disjointness or node-disjointness. Compared with link-disjoint protection, node-disjoint protection means higher degree of risk isolation and can accommodate both link failures and node failures. This motivates us to propose a hybrid node-disjoint protection, named Segment and Path Shared Protection (SPSP), to provide 100% protection against arbitrary simultaneous double-node failures (the worst double-failure case). For each service connection request, SPSP first provisions backup segments for the working segments, respectively, as the primary backup resources, then provisions a single backup path for the whole working path as the second backup resource. In addition to its complete protection capability and flexible scalability for double failures, SPSP can also obtain better network load balance and resource sharing degree by dynamic link-cost adjustment and reserved backup resource sharing. Simulation results show that SPSP can achieve a shorter average recovery time than path shared protection (PSP) and higher resource utilization and lower blocking probability than segment shared protection (SSP).     

星上双频段多通道微波光子链路传输性能的优化研究

利用星上微波光子技术,将多个频段微波信号调 制到光域,可解决数据在星上的高 速处理和星间远距离传输等问题。当多频段微波信号进行 光学调制时,交调失真是影响星上多频段微波信号光域传输性能的重要因素。研究了星上双 频段、每个频段内2信道的微波信号光学调制方法,分别推导了Ku、Ka波段微波信号的输出 信号噪声失真比(SNDR)和无杂散动态范围(SFDR)表达式,分析了 各次谐波和各阶交调失真分量对链路性能 的影响,获得了保证链路输出SNDR最优的最佳直流偏置相位和调制系 数。利用OptiSystem软件建立了仿真模型,并进行了仿真验证。研究结果表明 ,Ku 频段中非线性交调分量包括自频段三阶交调(IMD3)分量、频段间IMD3分量 和频段间二阶交调(IMD2)分量;Ka频段中非线性交调分量包括自频段IMD3分量、Ku频段IMD2分量、Ku频段二次谐波(HD2)分量以及频段间IMD3分量。对于Ku频 段信号,当调制系数和直流偏置相位分别为0.17和0.535π时,SNDR取得最优值21.50dB;对于Ka频段信号,调制系数和直流偏置相 位分别为0.22和0.525π时,SND R取得最优值15.32dB。