基于分散式查找的Web服务器集群

随着www用户快速增加，人们对Web服务器的需求也越来越高，集群是解决这个问题的一种重要方案。但是现有的Web服务器集群还存在自适应性差、有系统瓶颈等不足。该文在分散式查找算法Pastry的基础之上，提出，一种新的Web服务器集群方案。它具有分散式查找算法的诸多优点，如可扩展、自组织、高容错和分散特性，较好地克服了传统Web服务器集群方案的不足。     

一种快速IPv6路由查找方案

提出了一个可硬件实现的基于分段的快速IPv6路由查找方案.该方案支持快速的IP地址查找,并能有效地对路由前缀进行插入和删除操作.方案采用基于比特位置区分的压缩算法,与其它的 IPv6 路由查找方案相比较,所需存储器空间小,路由查找的平均时间少.如果采用SRAM流水线查找,可实现 125×106次/秒的查找速度.由于缺少实际的 IPv6路由前缀,该文生成了模拟路由前缀数据库.仿真试验结果表明:文章提出的方案具有合理的查找时间、空间和更新复杂度,容易硬件实现.     

具有逻辑路由跳数O(1)的可扩展的分散式查找算法

对等网络中的一个基本问题就是如何高效地进行数据查找．分散式查找是解决这类问题的一种新思路．现有的分散式查找方法在查找时所需的逻辑路由跳数都与网络中的节点数相关(一般为O(logn)，少数为O(n^1/c)．Sifter是一种可扩展、自组织、高容错和高效率的分散式查找算法．在该算法中，单个节点只需维护O(n1／c)个其他节点的链接信息，就能够在O(1)个逻辑路由跳内找到目的数据．该算法适用于网络动态性不大，但是对查找的实时性要求较高的应用．     

组合小波分析与神经网络的船舶缆绳载荷预测

通过对几种改进的二分查找算法的分析和总结,提出了一种基于结点群的更为高效的动态二分查找器。该二分查找器不仅使查找效率得以提高,而且使存储结构得以改进,既实现了动态的实时查找,又便于灵活地进行元素尤其是元素群的插入、删除等操作。另外,实验表明,当在大量数据中查找时,该算法明显优于以前改进的所有二分查找算法。     

基于按位段分块的映射查找法

本文提出一种基于按位段分块的映射查找新方法，该方法具有快速高效、不受数据类型与范围限制的特点。其理论意义和实用价值在于在查找中引入了按位段映射的思想，实现了平均时间复杂度为Ｏ（ｌｏｇ２（Ｎ／Ｍ））的快速查找。     

基于TCAM的并行路由查找方案综述

基于三态内容寻址存储器TCAM(Ternary Content-Addressable Memory)的路由查找方案是目前高性能路由器进行路由查找时普遍使用的方案,但这种方案仍存在查找速度、功耗和更新效率方面的挑战。因此,学者们提出了各种并行TCAM的解决方案以提高查找速度、降低功耗和增强更新效率。归类总结目前的并行TCAM路由查找方案,剖析它们的优缺点,指出目前这些方案仍存在的不足,并探索相应的解决方案。     

Leaf-TCAM:一种并行IP路由查找方法及性能分析

分析了互联网路由表和路由更新的特征,提出了一种基于叶子节点进行路由表分区的并行IP路由查找方法Leaf-TCAM,分区子表按照流量特征在K个TCAM芯片中进行均衡分布。分析表明,该路由查找方法在引入0.1*(K-1)冗余的前提下具有K-1倍加速因子。该方法无需进行前缀扩展,90%以上的路由前缀无需排序,可以采用随机更新;同时还具有分区均匀、分区溢出代价小等特点,而功耗只有传统单片方案的12%。     

CRL的一种改进方案

提出了一种改进的CRL方案,通过对CRL结构的改进,大大减少了证书用户查找撤销证书的时间。方案使用的基于排序的折半查找算法比较成熟,整体方案易于实现。     

一种Flash运行时注入查找工具的设计

为提高Flash运行时系列软件的质量,提升查找注入的效率,文章在之前注入查找技术的基础上,重新设计了一个自动化查找注入的工具。该工具的前端查找程序整合了路径查找、运行进程和查找算法策略等模块,可以跨平台运行。同时,该前端查找程序可灵活的运用优化策略进行查找,具有良好的适应性和扩展性。该工具的后端分析程序可根据实际测试环境情况来计算,从而选择最优算法作为查找策略,并且可对导致注入的源头信息进行分析,进一步缩小查找范围,结合选取的算法提出更为优化的查找策略。该后端分析程序还包括了校验注入和计算Build的置信水平用于整个测试的反馈。文章综合了各类查找算法和Flash运行时系列软件的工作特点,提升了注入查找能力,在实践中具有较强的应用价值。     

基于TCAM技术的高速路由查找方案

基于TCAM技术提出一个高速路由查找方案。该方案可以达到每秒钟100M次的查找速度，满足OC48和OC192接口的线速转发要求。方案使用了索引表和映射表的二级结构存储路由的下一跳信息，大大减小了存储空间，同时对IPv6具有很好的扩展性。对TCAM的路由更新问题进行了讨论，提出一个最坏情况下O(W／2)的更新算法(形为前缀长度集合的数目)，有效地提高了TCAM的更新性能。     

Intra-domain routing convergence with centralized control

The decentralized control scheme for routing in current IP networks has been questioned, and a centralized routing scheme has been proposed as an alternative. In this paper, we compare the convergence of centralized control scheme with decentralized link-state routing protocols. We first review the architectural advantages and challenges of centralized control. Thereafter, we identify and discuss the components of the convergence time in both schemes. We present how to achieve fast routing convergence in networks with centralized control. In particular, we analyze how to distribute forwarding information efficiently. Finally, we perform simulation studies on the convergence time for both real and synthetic network topologies and study the impact of control element location, link weights, and number of failures on the convergence time. The results show that the centralized control scheme can provide faster routing convergence than link-state routing protocols.     

Cloaking locations for anonymous location based services: a hybrid approach

An important privacy issue in Location Based Services is to hide a user’s identity while still provide quality location based services. Previous work has addressed the problem of locational -anonymity either based on centralized or decentralized schemes. However, a centralized scheme relies on an anonymizing server (AS) for location cloaking, which may become the performance bottleneck when there are large number of clients. More importantly, holding information in a centralized place is more vulnerable to malicious attacks. A decentralized scheme depends on peer communication to cloak locations and is more scalable. However, it may pose too much computation and communication overhead to the clients. The service fulfillment rate may also be unsatisfied especially when there are not enough peers nearby. This paper proposes a new hybrid framework called HiSC that balances the load between the AS and mobile clients. HiSC partitions the space into base cells and a mobile client claims a surrounding area consisting of base cells. The number of mobile clients in the surrounding cells is kept and updated at both client and AS sides. A mobile client can either request cloaking service from the centralized AS or use a peer-to-peer approach for spatial cloaking based on personalized privacy, response time, and service quality requirements. HiSC can elegantly distribute the work load between the AS and the mobile clients by tuning one system parameter base cell size and two client parameters - surrounding cell size and tolerance count. By integrating salient features of two schemes, HiSC successfully preserves query anonymity and provides more scalable and consistent service. Both the AS and the clients can enjoy much less work load. Additionally, we propose a simple yet effective random range shifting algorithm to prevent possible privacy leakage that would exist in the original P2P approach. Our experiments show that HiSC can elegantly balance the work load based on privacy requirements and client distribution. HiSC provides close to optimal service quality. Meanwhile, it reduces the response time by more than an order of magnitude from both the P2P scheme and the centralized scheme when anonymity level(value of ) or number of clients is large. It also reduces the update message cost of the AS by nearly 6 times and the peer searching message cost of the clients by more than an order of magnitude.

Distributed cell-centric neighborhood-related location area planning for PCS networks

An intelligent location area planning (LAP) scheme should consider the frequent replannings of location areas (LAs) due to changes in user distribution and mobility patterns along with optimization of location management costs, including location updating and paging costs. Most schemes proposed in the literature are designed through centralized techniques, thus requiring more computing time to plan the LAs. Frequent replannings to accommodate environmental changes make the situation worse. As to the optimization of location management costs, most proposed schemes consider the inter-cell crossing rate as one of the key factors in determining the optimal partitions. In some cases, the inter-cell crossing rate may lead to an unsatisfactory outcome. Another problem is the ping-pong effect which is caused by the fixed borders between any two of LAs. In this paper, we propose a distributed cell-centric neighborhood-related LAP scheme in which each cell acts as the center of an LA and in which highly correlative neighboring cells are bundled into the LA if mobile terminals (MTs) remain within the LA long enough to reduce costs. Moreover, the ping-pong effect will be alleviated because MTs always locate at the center cell of an LA whenever a new location update is performed. Finally, the scheme can be implemented in a distributed manner so the computing time incurred by frequent replannings can be reduced. Simulation results show that our scheme indeed exhibits excellent results.     

Centralized and decentralized asynchronous optimization ofstochastic discrete-event systems

We propose and analyze centralized and decentralized asynchronous control structures for the parametric optimization of stochastic discrete-event systems (DES) consisting of K distributed components. We use a stochastic approximation type of optimization scheme driven by gradient estimates of a global performance measure with respect to local control parameters. The estimates are obtained in distributed and asynchronous fashion at the K components based on local state information only. We identify two verifiable conditions for the estimators and show that if they, and some additional technical conditions, are satisfied, our centralized optimization schemes, as well as the fully decentralized asynchronous one we propose, all converge to a global optimum in a weak sense. All schemes have the additional property of using the entire state history, not just the part included in the interval since the last control update; thus, no system data are wasted. We include an application of our approach to a well-known stochastic scheduling problem and show explicit numerical results using some recently developed gradient estimators     

Nonlinear Model Predictive Formation Flight

This correspondence paper presents the validation of a formation-flight control technique with obstacle avoidance capability based on nonlinear model predictive algorithms. Control architectures for multiagent systems employed in this correspondence paper can be categorized as centralized, sequential-decentralized, and fully decentralized methods. Centralized methods generally have better performance than decentralized methods. However, it is well known that the performance of the centralized methods for formation flight degrades when there exists communication failure among the vehicles, and they require more computation time than the decentralized method. This correspondence paper evaluates the control performance and the computation time reduction of the sequential-decentralized and fully decentralized methods in comparison with the centralized method and shows that the fully decentralized method can be made effective against short-term communication failure. The control inputs for formation flight are computed by nonlinear model predictive control (NMPC). The control input saturation and state constraints are incorporated as inequality constraints using Karush–Kuhn–Tucker conditions in the NMPC framework, and the collision avoidance can be considered in real time. The proposed schemes are validated by numerical simulations, which include the process and measurement noise for more realistic situations.      

Design of decentralized robust load-frequency controller based on SVD method

A decentralized robust control scheme is presented for the load-frequency control of interconnected power systems with uncertain parameters. A singular value decomposition (SVD) technique and Lyapunov stability theory are adopted to implement a decentralized robust controller. The stability analysis of the closed-loop interconnected systems for all admissible uncertainties is discussed. The performance robustness of the proposed decentralized robust control scheme has been verified through simulation studies on a two-area power system model. The effectiveness of the decentralized control algorithm is compared to that of a centralized robust one. It has been found that both control schemes have almost the same performance with integral control action in the presence of parametric uncertainty in the plant.     

Cell-related location area planning for 4G PCS networks with variable-order Markov model

Location management is a critical issue in personal communication service (PCS) networks, tracking the location of user equipment (UE) with the goal of minimizing total signaling cost. Previous work can be classified into two categories: static and dynamic. Static schemes partition networks into fixed size LAs. However, these schemes are inefficient because they do not take UEs’ mobility and the call arrival rate into account. On the other hand, focusing on individual UEs, dynamic schemes have minimized the location management cost. However, they are difficult to implement because recording the individual information of numerous UEs and planning each of their LAs consume uncontrollable cost. Because of these reasons, we propose a cell-based scheme between static and dynamic schemes. Considering people usually stay in specific zones for long periods and the movement of UEs usually presents a strong moving direction in areas, this study presents a distributed algorithm by employing variable-order Markov models to find the mobility characteristic shared by UEs to plan better LAs with lower location management cost. When the order of Markov model is set to 1, our method is equal to a pure cell-centric LAP scheme; while the order of Markov model is high, it is more like a profile-based dynamic scheme. So, the setting of the order actually is a trade-off problem between the overall location management cost and the computing complexity. We present to retrieve a balance by using the expected location management cost and the number of total states of Markov models. In simulations, the origin–destination matrix (O–D matrix) from the Taipei Rapid Transit Corporation is used for representing the association between two cells. Simulation results demonstrate that the proposed scheme achieves good performance.     

Supporting location/identity separation in mobility-enhanced satellite networks by virtual attachment point

Location/identity separation can be used to enhance mobility in satellite networks. However, given the high mobility of non-geostationary satellite networks, usage of conventional binding update schemes will inevitably result in a large number of binding updates. In this work, a novel virtual attachment point based indirect binding scheme is proposed to address this issue. Moreover, a multi-layer service area based vertical update scheme is further investigated to eliminate the ping-pong effect. A random walk model based analysis and a Monte carlo method based simulation are conducted to evaluate our schemes. And the evaluation results demonstrate the validity and efficiency of our schemes comparing to conventional scheme, i.e. mobile IP.     

基于动态累加器的去中心化加密搜索方案

近年来区块链技术取得广泛关注,涌现出众多基于区块链技术的新型应用,其中以 StorJ、Filecoin为代表的去中心化存储应用取得了较好的市场反响。对比传统中心化存储,去中心化存储为用户提供了全新的数据存储思路,令用户在获得更好的服务伸缩性的同时,有效降低数据存储的成本。但在现有的去中心化存储方案中,用户的隐私不能得到有效保护。基于此,介绍了一种利用加密搜索技术对去中心化存储方案进行加强的方法。新方法将动态累加器算法引入加密搜索过程中,保障用户存储内容隐私并提供了更好的加密搜索性能。