Clustering of wireless sensor and actor networks based on sensor distribution and connectivity

Wireless Sensor and Actor Networks (WSANs) employ significantly more capable actor nodes that can collect data from sensors and perform application specific actions. To take these actions collaboratively at any spot in the monitored regions, maximal actor coverage along with inter-actor connectivity is desirable. In this paper, we propose a distributed actor positioning and clustering algorithm which employs actors as cluster-heads and places them in such a way that the coverage of actors is maximized and the data gathering and acting times are minimized. Such placement of actors is done by determining the k-hop Independent Dominating Set (IDS) of the underlying sensor network. Basically, before the actors are placed, the sensors pick the cluster-heads based on IDS. The actors are then placed at the locations of such cluster-heads. We further derive conditions to guarantee inter-actor connectivity after the clustering is performed. If inter-connectivity does not exist, the actors coordinate through the underlying sensors in their clusters to adjust their locations so that connectivity can be established. The performances of the proposed approaches are validated through simulations.     

Maximizing connected coverage via controlled actor relocation in wireless sensor and actor networks

Wireless sensor and actor networks (WSANs) have recently emerged with the idea of combining wireless sensor networks (WSNs) and mobile ad hoc networks (MANETs). In addition to resource constrained sensors, resource rich and mobile actor nodes are employed in WSANs. These actors can collect data from the sensors and perform appropriate actions as a result of processing such data. To perform the actions at all parts of the region in a timely manner, the actors should be deployed in such a way that they might be able to communicate with each other and cover the whole monitored area. This requires that the actors should be placed carefully prior to network operation in order to maximize the coverage and maintain the inter-actor connectivity. In this paper, we propose a distributed actor deployment algorithm that strives to maximize the coverage of actors without violating the connectivity requirement. The approach applies repelling forces between neighboring actors and from the sensors that sit on the boundaries in order to spread them in the region. The spreading of the nodes is done using a tree of actors which can provide more freedom for the movement of the nodes but at the same time maintain the required connectivity among the nodes. We present two techniques for creation of such an actor tree which are based on local pruning of the actor links and spanning tree of the inter-actor network. The performance of our approach is validated both analytically and experimentally.     

无线传感器/反应器网络中反应节点优化重定位机制研究

针对无线传感器/反应器网络中因多个反应器失效而造成的反应器网络连通性被破坏问题,以网络流理论为基础,提出了一个基于网络流的多目标规划模型来求解优化的反应器重定位方案。模型将反应器网络看成是一个运输网络,通过流平衡条件来重建反应器网络的连通性。最小化多个参与恢复的反应器总体开销和最小化单个反应器的最大开销是该模型的两个优化目标。仿真实验结果表明,基于该模型的优化重定位方案能够有效地恢复因多反应器节点失效而造成的网络连通性问题。     

Movement-Assisted Connectivity Restoration in Wireless Sensor and Actor Networks

Recent years have witnessed a growing interest in applications of wireless sensor and actor networks (WSANs). In these applications, a set of mobile actor nodes are deployed in addition to sensors in order to collect sensors' data and perform specific tasks in response to detected events/objects. In most scenarios, actors have to respond collectively, which requires interactor coordination. Therefore, maintaining a connected interactor network is critical to the effectiveness of WSANs. However, WSANs often operate unattended in harsh environments where actors can easily fail or get damaged. An actor failure may lead to partitioning the interactor network and thus hinder the fulfillment of the application requirements. In this paper, we present DARA, a Distributed Actor Recovery Algorithm, which opts to efficiently restore the connectivity of the interactor network that has been affected by the failure of an actor. Two variants of the algorithm are developed to address 1- and 2-connectivity requirements. The idea is to identify the least set of actors that should be repositioned in order to reestablish a particular level of connectivity. DARA strives to localize the scope of the recovery process and minimize the movement overhead imposed on the involved actors. The effectiveness of DARA is validated through simulation experiments.     

基于重叠区域的无线传感反应网络连接性恢复机制

针对无线传感反应网络(WSAN)中反应节点的失效导致的网络连接性被破坏问题,提出了一种新的网络连接性恢复机制。反应节点首先根据2跳网络拓扑信息来确定是否为局部关键节点,然后利用反应节点间存在的管理区域的重叠性来计算新的移动位置,最后采用局部级联重定位方式来实现连接性的恢复。通过NS2仿真结果表明,该机制能够正确恢复网络的连接性并实现较小的恢复开销。     

无线传感器/执行器网络中能量有效的实时分簇路由协议

无线传感器/执行器网络(WSANs)主要应用于自动控制领域,实时性问题是其面临的首要挑战.根据实际环境中的节点部署情况,建立了系统模型;研究了分簇策略与功率控制技术对于自组织网络实时性的影响,提出了一种可适用于WSANs的能量有效的实时分簇路由协议--RECRP协议.该协议采用二级成簇策略使网络中的各类节点稳定分簇.分簇后的各类节点具有不同发射功率,利用执行器节点的强大通信能力有效降低网络延时.采用能量有效性算法使网络中的传感器节点轮换担任簇首,从而使网络能量均匀消耗,延长网络的生存时间.实验结果证明,在WSANs中RECRP协议可使网络稳定分簇,并且在网络的实时性与能量有效性方面与现有典型路由协议相比具有更优越的性能.     

一种有效的社会网络社区发现模型和算法

社会网络的社区发现存在划分效果较好的算法时间复杂度过高、现有快速划分算法划分质量不佳、缺乏表达和充分利用个体和链接属性信息的模型和机制等问题.针对这些问题,提出了一种边稳定系数模型和一种能表达个体间关系紧密度的完全信息图模型,在此基础上设计和实现了一种有效的社区发现算法.提出的完全信息图模型具有较高通用性,适用于需要融合个体和链接属性的社区发现算法.通过系列实验表明,所提出的以边稳定系数模型和完全信息图为基础的算法,对社会网络中的社区发现问题是有效的.算法不仅具有较快的速度,也能适用于带权与不带权的网络,得到的社区划分结果也具有较高的划分质量.     

Comparison of recovery schemes to maximize restorable throughput in multicast networks

Multicast networks have many applications especially in real-time content delivery systems. For high-quality services, users do not expect to witness any interruption; thus, network link failure has to be handled gracefully. In unicast networks there are many approaches for dealing with link failures using backup paths. Recently, Cohen and Nakibly categorized these methods, provided linear programming formulations for optimizing network throughput under the assumption that the paths are splitable, and compared them experimentally. In this work, we take their approach and apply to the multicast failure recovery problem. We propose backup bandwidth allocation algorithms based on linear programs to maximize the throughput, and perform an experimental study on the performance of recovery schemes. We study many recovery schemes in multicast networks and propose a new recovery scheme that performs better than all other recovery scheme except the one that recomputed the whole multicast tree from scratch for each link failure.     

链路跟踪在多出口网络链路互备中的应用研究

提出了一种利用链路跟踪检测技术并结合策略路由监控本地网络到多个ISP网络连通性的技术方案，克服了传统的使用静态路由方法对于因某一ISP网络发生故障时，无法实现路由实时检测和瞬时切换通路的技术缺陷，有效地实现了多出口网络的链路互备和负载均衡，从根本上解决了数据中心断网的难题。结合典型实例验证了该技术方案的可行性，为解决多出口网络中的相关具体问题提供了一条切实可行的途径。     

Protection based on backup radios and backup fibers for survivable Fiber-Wireless (FiWi) access network

In Fiber-Wireless (FiWi) access network, the optical back-end is vulnerable to the network component failure due to its tree topology. Any failure at the optical back-end may cause huge data loss. Thus, the survivability in FiWi is an important issue, especially the protection for the optical back-end. Some works propose to protect the optical back-end in FiWi by means of the wireless rerouting in the wireless front-end. However, these works cannot guarantee that there are always the available wireless paths for the traffic rerouting. In this paper, we divide the failures at the optical back-end into ONU-level failure and OLT-level failure according to the failure severity. To tolerate the ONU-level failure, we allocate each ONU a partner ONU and establish the wireless-backup-path between them by deploying backup radios on the traversed wireless routers. To tolerate the OLT-level failure, we cluster all segments in the network and place the backup fibers among the segments in each cluster to establish the protection ring. Thus, each pair of segments in the same cluster can backup for each other along the optical-backup-paths on the protection ring. We propose the heuristic algorithms to minimize the cost of backup radios and the cost of backup fibers. The simulation results demonstrate that the proposed algorithms are effective in enhancing the survivability of FiWi, while requiring less cost than the previous works.     

Dynamic Path Management with Resilience Constraints under Multiple Link Failures in MPLS/GMPLS Networks

Most previous research on MPLS/GMPLS recovery management has focused on efficient routing or signaling methods from single failures. However, multiple simultaneous failures may occur in large-scale complex virtual paths of MPLS/GMPLS networks. In this paper, we present a dynamic MPLS/GMPLS path management strategy in which the path recovery mechanism can rapidly find an optimal backup path which satisfies the resilience constraints under multiple link failure occurrences. We derived the conditions to test the existence of resilience-guaranteed backup path, and developed a decomposition theorem and backup path construction algorithm for the fast restoration of resilience-guaranteed backup paths, for the primary path with an arbitrary configuration. Finally, simulation results are presented to evaluate the performance of the proposed approach.     

Traffic recovery time constrained shared sub-path protection algorithm in survivable WDM networks

With the development of real-time applications, the traffic recovery time, which is defined as the duration between the failure occurrence on the working path and the interruptive traffic has been successfully switched to the backup path, has become the basic Quality-of-Service (QoS) requirement in survivable WDM networks. In this paper, we address the problem of shared sub-path protection with considering the constraint of traffic recovery time and propose a new heuristic algorithm called Traffic recovery time Constrained Shared Sub-Path Protection (TC_SSPP) to compute the working path and the Shared-Risk-Link-Group (SRLG)-disjoint backup sub-paths. The main target of our work is to improve the resource utilization ratio and reduce the blocking probability for dynamic network environment. By properly setting the delay parameter for each link and running the Delay Constrained Shortest Path Algorithm (DCSPA) to compute the backup sub-paths, TC_SSPP can effectively guarantee the traffic recovery time. Simulation results show that the proposed TC_SSPP can outperform the traditional algorithms.     

Coverage-aware connectivity restoration in mobile sensor networks

Mobile sensor networks rely heavily on inter-sensor connectivity for collection of data. Nodes in these networks monitor different regions of an area of interest and collectively present a global overview of some monitored activities or phenomena. A failure of a sensor leads to loss of connectivity and may cause partitioning of the network into disjoint segments. A number of approaches have been recently proposed that pursue node relocation in order to restore connectivity. However, these approaches tend to ignore the possible loss of coverage in some areas, either due to the failure itself or due to the connectivity-limited focus of the recovery. This paper fills this gap by addressing the connectivity and coverage concerns in an integrated manner. A novel coverage conscious connectivity restoration (C³R) algorithm is presented. C³R involves one or multiple neighbors of the failed node to recover from the failure. Each neighbor temporarily relocates to substitute the failed node, one at a time, and then returns back to its original location. This leads to intermittent connectivity and monitoring of all the originally covered spots. This paper also presents energy-centric optimized recovery algorithm (ECR), an optimized version of C³R that is geared for energy efficiency. Both C³R and ECR are validated through simulation. The simulation results confirm the effectiveness of these approaches.     

基于优化链路权值的域内路由保护方案

目前,互联网部署的域内链路状态路由协议,如开放最短路径优先(Open Shortest Path First,OSPF)和中间系统到中间系统(Intermediate System-to-Intermediate System,IS-IS),采用被动恢复方案应对网络故障。随着网络的发展,大量的实时应用部署在互联网上,OSPF的收敛时间无法满足这些实时应用对收敛时间的需求。因此,学术界和工业界提出采用路由保护方案来应对网路中出现的故障。然而,已有的路由保护方案存在两个方面的问题:1)默认路径和备份路径的交叉度较高,如LFA；2)为了计算两条交叉度低的路径,对默认路径加以限制,即默认路径不采用最短路径,如Color Tree。为了解决上述两个问题,首先将上述问题归结为整数规划模型,接着利用启发式方法计算近似最优解,最后在实际网络和模拟网络中对所提算法进行了大量实验。实验结果表明,所提算法可以降低默认路径和备份路径的交叉度,极大地提高网络的可用性。     

Software-Based Failure Detection and Recovery in Programmable Network Interfaces

Emerging network technologies have complex network interfaces that have renewed concerns about network reliability. In this paper, we present an effective low-overhead fault tolerance technique to recover from network interface failures. Failure detection is based on a software watchdog timer that detects network processor hangs and a self-testing scheme that detects interface failures other than processor hangs. The proposed self-testing scheme achieves failure detection by periodically directing the control flow to go through only active software modules in order to detect errors that affect instructions in the local memory of the network interface. Our failure recovery is achieved by restoring the state of the network interface using a small backup copy containing just the right amount of information required for complete recovery. The paper shows how this technique can be made to minimize the performance impact to the host system and be completely transparent to the user.     

A destination-based approach for cut detection in wireless sensor networks

Wireless sensor networks often suffer from disrupted connectivity caused by its numerous aspects such as limited battery power of a node and unattended operation vulnerable to hostile tampering. The disruption of connectivity, often referred to as network cut, leads to ill-informed routing decisions, data loss and waste of energy. A number of protocols have been proposed to efficiently detect network cuts; they focus solely on a cut that disconnects nodes from the base station. However, a cut detection scheme is truly useful when a cut is defined with respect to multiple destinations (i.e. target nodes), rather than a single base station. Thus, we extend the existing notion of cut detection, and propose an algorithm that enables sensor nodes to autonomously monitor the connectivity to multiple target nodes. We introduce a novel reactive cut detection solution, the point-to-point cut detection, where given any pair of source and destination, a source is able to locally determine whether the destination is reachable or not. Furthermore, we propose a lightweight proactive cut detection algorithm specifically designed for a network scenario with a small set of target destinations. We prove the effectiveness of the proposed algorithms through extensive simulations; specifically, in our network configurations, proposed cut detection algorithms achieve more than an order of magnitude improvement in energy consumption, when coupled with an underlying routing protocol.     

面向仓储系统的自动化WSAN“感知一控制”模型研究

建立正确的“感知一控制”模型是实现基于RFID和WSAN的物流仓储系统的关键。研究执行器节点自主移动环境下的多维事件协作检测和跟踪算法;研究基于合同网协议和多竞价拍卖算法的多执行器节点实时任务分配方法,并利用WSAN动态拓扑度相关性和网络同步能力的关系研究执行器的牵制控制策略;同时,基于神经网络模型和竞合博弈模型设计执行器节点的移动控制策略和编队控制策略。模型的有效性可利用扩展的UML建模方法和XMSF集成框架来评估。     

基于拥塞及内存感知的SD-WAN故障恢复

在软件定义广域网(SD-WAN)中, 链路故障会导致大量丢包, 严重时会引起部分网络瘫痪. 现有的流量工程方法通过在数据平面提前安装备份路径能够加快故障恢复过程, 但在资源受限的情况下难以适应各种网络故障情况, 从而使恢复后的网络性能下降. 为了保证网络在故障恢复之后的性能并减少备份资源的消耗, 本文提出一种基于拥塞及内存感知的主动式故障恢复方案(CAMA), 不仅能够将受影响数据流进行快速重定向, 还能实现负载均衡避免恢复后潜在的链路拥塞. 实验结果表明, 与已有方案相比, CAMA能有效利用备份资源, 在负载均衡上有较好的性能, 且仅需少量备份规则即可覆盖所有单链路故障情况.     

Orchestration and analysis of decentralized workflows within heterogeneous networking infrastructures

This paper applies the Network Edge Workflow Tool (Newt) to decentralized causal workflows in dynamic heterogeneous wireless networks. We build on previous work applying a Newt prototype to an emergency response scenario and extend in two ways: we apply Newt to a far more advanced use case which models distributed complex causal processing and interactions; and second, we apply time-windowed conversational graphs to analyze the distributed workflow. In addition to the prior disaster recovery use case, we apply Newt to the orchestration of William Shakespeare’s Hamlet by distributing the actors across a wireless network and have actors converse their lines as decentralized messages of communication between one actor and another as the play progresses. We construct and analyze conversational graph models for the Hamlet workflow by comparing an a priori baseline model and a post facto estimate resulting from measurements of network conversational adjacencies during the execution of the workflow.     

基于网络编码的文件备份方案

针对数据备份需占用大量空间和需额外手段对其安全保密性进行保护的问题,提出了一种基于网络编码技术的文件备份方案,其核心是对多个备份文件进行网络编码操作,生成编码备份文件后存储于备份服务器中。该方案包括以下部分:备份的基本原理、备份过程、文件更新对备份恢复的影响和处理、备份的更新和全局备份控制系统。实验与理论分析表明,该方案较传统备份方案大幅节省了存储空间,提高了备份文件的安全保密性,但文件的可恢复性微降并增加了系统的复杂度。