Risk-based attack strategies for mobile ad hoc networks under probabilistic attack modeling framework

In this paper, we introduce and design a modeling framework that allows for the study and analysis of attack propagation in mobile ad hoc networks. The choice of a statistical approach for the problem is motivated by the dynamic characteristics of the ad hoc topology and the stochastic nature of threat propagation. Based on this probabilistic modeling framework, we study the impact of topology and mobility in the propagation of software threats over ad hoc networks. We design topology control algorithms that indicate how to properly adjust an attacker’s transmission radius, according to the measured topological characteristics and availability of its resources, in the process of infecting a network more effectively. Then based on these topology control algorithms we develop different attack strategies that may range from independent attacks to cooperative scenarios in order to increase the negative impact of an attack on the network. Our performance evaluation results demonstrate that the proposed topology control algorithms and respective attack strategies effectively balance the tradeoffs between the potential network damage and the attackers’ lifetime, and as a result significantly outperform any other flat and threshold-based approaches.     

有向无环图上k步可达查询优化算法

k步可达查询用于在给定的有向无环图（DAG）中回答两点之间是否存在长度不超过k的路径。针对现有方法的索引规模大、查询处理效率低的问题,提出一种基于部分点的双向最短路径索引来提升索引的可达信息覆盖率,并提出一组优化规则来减小索引规模;然后提出基于简化图的正反互逆拓扑索引来加速回答不可达查询;最后提出远距离优先的双向遍历策略来提高查询处理的效率。基于21个真实数据集（如引用网络、社交网络等）的实验结果表明,相比已有的高效方法PLL及BFSI-B,所提出的算法具有更小的索引规模和更快的查询响应速度。     

无线传感器网络中基于聚簇结构的Skyline查询方法

现有的基于单服务器的Skyline查询算法已经不能很好地应用于无线传感器网络这类分布式多跳自组织网络中。基于聚簇结构的Skyline查询算法就是针对 这类特定的网络结构而提出的。该算法采用基于聚簇的路由结构,为了减少Skyline查询处理过程中传感器节点的通信开销,挑选具有最大支配力的数据元组作为全局过滤元组来过滤不满足Skyline条件的数据。同时,在Skyline查询处理过程中引入滑动窗口机制,该机制也能有效地降低通信开销。大量的仿真实验结果显示,所提Skyline查询算法在确保能耗的基础上仍然具有很好的性能。     

Energy saving strategies for cooperative cache replacement in mobile ad hoc networks

Data caching on mobile clients is widely seen as an effective solution to improve system performance. In particular, cooperative caching, based on the idea of sharing and coordination of cache data among multiple users, can be particularly effective for information access in mobile ad hoc networks where mobile clients are moving frequently and network topology is changing dynamically. Most existing cache strategies perform replacement independently, and they seldom consider coordinated replacement and energy saving issues in the context of a mobile ad hoc network. In this paper, we analyse the impact of energy on designing a cache replacement policy and formulate the Energy-efficient COordinated cache Replacement Problem (ECORP) as a 0-1 knapsack problem. A dynamic programming algorithm called ECORP-DP and a heuristic algorithm called ECORP-Greedy are presented to solve the problem. Simulations, using both synthetic workload traces and real workload traces in our experiments, show that the proposed policies can significantly reduce energy consumption and access latency when compared to other replacement policies.     

Cross-layer routing for peer database querying over mobile ad hoc networks

The widespread of mobile ad hoc networking calls for a careful design of network functions in order to meet the application requirements and economize on the limited resources. In this paper we address the problem of distributing query messages among peers in mobile ad hoc networks. We assume that peers are organized in classes. Each peer possesses a local database and can answer queries posed by other peers. Each peer can also pose queries to all the peers belonging to a certain class or classes. Contrary to traditional p2p lookup queries, we are interested in collecting answers from as many peers as possible. We propose a query routing protocol, called CL-QF, which is based on a novel cross-layer design. The purpose of this design is to incorporate application layer specifics (e.g., class information) into the network layer in order to reduce transmissions therefore economize on resources. CL-QF coexists with traditional routing. This synergy minimizes the complexity and signaling of CL-QF while the network is able to seamlessly provide legacy unicast communication. CL-QF manages a reduction of up to ～78% compared to non-cross-layer approaches, such as probabilistic forwarding, without compromising the ability to effectively collect replies.     

A collaborative learning approach for geographic information retrieval based on social networks

Nowadays, spatial and temporal data play an important role in social networks. These data are distributed and dispersed in several heterogeneous data sources. These peculiarities make that geographic information retrieval being a non-trivial task, considering that the spatial data are often unstructured and built by different collaborative communities from social networks. The problem arises when user queries are performed with different levels of semantic granularity. This fact is very typical in social communities, where users have different levels of expertise. In this paper, a novelty approach based on three matching-query layers driven by ontologies on the heterogeneous data sources is presented. A technique of query contextualization is proposed for addressing to available heterogeneous data sources including social networks. It consists of contextualizing a query in which whether a data source does not contain a relevant result, other sources either provide an answer or in the best case, each one adds a relevant answer to the set of results. This approach is a collaborative learning system based on experience level of users in different domains. The retrieval process is achieved from three domains: temporal, geographical and social, which are involved in the user-content context. The work is oriented towards defining a GIScience collaborative learning for geographic information retrieval, using social networks, web and geodatabases.     

Minimum disruption service composition and recovery in mobile ad hoc networks

The dynamic nature of mobile ad hoc networks poses fundamental challenges to the design of service composition schemes that can satisfy the end-to-end quality of service requirements and minimize the effect of service disruptions caused by dynamic link and node failures. Although existing research on mobile ad hoc networks has focused on improving reliability, little existing work has considered service deliveries spanning multiple components. Moreover, service composition strategies proposed for wireline networks (such as the Internet) are poorly suited for highly dynamic wireless ad hoc networks.This paper proposes a new service composition and recovery framework designed to achieve minimum service disruptions for mobile ad hoc networks. The framework consists of two tiers: service routing, which selects the service components that support the service path, and network routing, which finds the optimal network path that connects these service components. Our framework is based on the disruption index, which is a novel concept that characterizes different service disruption aspects, such as frequency and duration, that are not captured adequately by conventional metrics, such as reliability and availability.Using the definition of disruption index, we formulate the problem of minimum-disruption service composition and recovery (MDSCR) as a dynamic programming problem and analyze the properties of its optimal solution for ad hoc networks with known mobility plan. Based on the derived analytical insights, we present our MDSCR heuristic algorithm for ad hoc networks with uncertain node mobility. This heuristic algorithm approximates the optimal solution with one-step lookahead prediction, where service link lifetime is predicted based on node location and velocity using linear regression. We use simulations to evaluate the results of our algorithm in various network environments. The results validate that our algorithm can achieve better performance than conventional methods.     

CODISC: Collaborative and distributed semantic caching for maximizing cache effectiveness in wireless networks

In wireless mobile ad hoc networks (MANETs), a mobile node would normally acquire data from a data server through an access point by sending the server a request each time it needs data. To reduce the high costs normally associated with accessing remote servers (i.e., outside the MANET), data caching by the mobile nodes can be employed. Several caching techniques for MANETs have been proposed and implemented, including a cooperative scheme that we recently introduced. It employs a directory-based approach in which submitted queries are cached in the MANET to be used subsequently as indexes to corresponding data items (results). When a request is issued, nodes cooperate to find its answer (if it exists) and send it to the requesting node. In this paper, we extend this scheme by semantically comparing each submitted request with all cached queries. The semantic analysis process includes trimming the request into fragments and joining the answers of these fragments to produce the answer of the request. We study the performance of the proposed system both analytically and experimentally, and prove the advantageous features of the system relative to others in terms of query response time, generated traffic, and hit ratio.     

Web信任传播建模

个体之间的信任关系构成具有小世界特征的复杂网络,称为信任网（web of trust）。信任网中的信任传播建模是许多重要的电子商务系统中亟待解决的基本任务之一。引入属性相似度的概念,提出一个可用于电子商务、语义网和移动自组网等领域的信任传播模型,给出了一种计算属性相似度的推荐方法。实验结果表明,每个节点通过建立对有限的邻节点的信任度,可以较准确地预测出其对网络中任意陌生节点的信任度。     

Optimizing queries to remote resources

One key property of the Semantic Web is its support for interoperability. Recent research in this area focuses on the integration of multiple data sources to facilitate tasks such as ontology learning, user query expansion and context recognition. The growing popularity of such machups and the rising number of Web APIs supporting links between heterogeneous data providers asks for intelligent methods to spare remote resources and minimize delays imposed by queries to external data sources. This paper suggests a cost and utility model for optimizing such queries by leveraging optimal stopping theory from business economics: applications are modeled as decision makers that look for optimal answer sets. Queries to remote resources cause additional cost but retrieve valuable information which improves the estimation of the answer set’s utility. Optimal stopping optimizes the trade-off between query cost and answer utility yielding optimal query strategies for remote resources. These strategies are compared to conventional approaches in an extensive evaluation based on real world response times taken from seven popular Web services.     

移动ad hoc网络的安全漏洞及对策

移动ad hoc网络是一种新型的无线移动网络，因其特有的路由多跳性、无中心的控制分布性以及拓扑动态性，使得现有网络中的安全机制不能完全应用于移动ad hoc网络。文中探讨了移动ad hoc网络特有的各种安全漏洞以及相应的对策中存在的各种不足，并与现有网络中的安全对策进行了较深入的比较，从而总结出该领域研究的发展趋势，并指出了几个值得重视的研究方向。     

A visual tool for ontology alignment to enable geospatial interoperability

In distributed geospatial applications with heterogeneous databases, an ontology-driven approach to data integration relies on the alignment of the concepts of a global ontology that describe the domain, with the concepts of the ontologies that describe the data in the distributed databases. Once the alignment between the global ontology and each distributed ontology is established, agreements that encode a variety of mappings between concepts are derived. In this way, users can potentially query hundreds of geospatial databases using a single query. Using our approach, querying can be easily extended to new data sources and, therefore, to new regions. In this paper, we describe the AgreementMaker, a tool that displays the ontologies, supports several mapping layers visually, presents automatically generated mappings, and finally produces the agreements.     

Derived types in semantic association discovery

Semantic associations are direct or indirect linkages between two entities that are construed from existing associations among entities. In this paper we extend our previous query language approach for discovering semantic associations with an ability to retrieve semantic associations that, besides explicitly stated (base) associations, may contain associations derived using logic-based derivation rules. As will be shown, this makes it possible to find semantic associations that are both compact and intuitive. To implement this new feature, we introduce a rewriting principle that utilizes derived associations to reduce resulting semantic associations if possible. Other proposed means to assist the interpretation of query results include answer expansion and the ordering of answers. The incorporated answer expansion feature lets the user investigate rewritten semantic associations in a query result at the desired level of detail. The ordering of answers is based on the lengths of the resulting semantic associations, whereby priority is given to shorter semantic associations which often express close and relevant relationships.     

Ad Hoc网络多路径需求路由及路径熵选择算法

无线移动Ad Hoc网络是一种不依赖任何固定基础设施的移动无线多跳网络.由于其动态性和资源的限制,在Ad Hoc网络中提供多路径路由是一个重要的研究课题.描述了一种Ad Hoc网络中基于信息熵选择的稳定多路径路由算法(stability multipath on-demand routing,简称SMDR),提出了路径熵的度量参数,并利用路径熵来选择稳定的、长寿命的多路径,减少了重构路由的次数,从而在网络拓扑频繁变化的Ad Hoc网络环境中较好地提供QoS保证和提高数据传输率.仿真结果表明,SMDR协议改进了分组传输率、端到端时延和路由负载率.SMDR协议为解决动态的Ad Hoc网络多路径传输提供了一种新的有效途径.     

Reusing ontology mappings for query routing in semantic peer-to-peer environment

To efficiently support automated interoperability between ontology-based information systems in distributed environments, the semantic heterogeneity problem has to be dealt with. To do so, traditional approaches have acquired and employed explicit mappings between the corresponding ontologies. Usually these mappings can be only obtained from human domain experts. However, it is too expensive and time-consuming to collect all possible mapping results on distributed information systems. More seriously, as the number of systems in a large-scale peer-to-peer (P2P) network increases, the efficiency of the ontology mapping is exponentially decreased. Thereby, in this paper, we propose a novel semantic P2P system, which is capable of (i) sharing and exchanging existing mappings among peers, and (ii) composing shared mappings to build a certain path between two systems. Given two arbitrary peers (i.e., source and destination), the proposed system can provide indirect ontology mappings to make them interoperable. In particular, we have focused on query-based communication for evaluating the proposed ontology mapping composition system. Once direct ontology mappings are collected from candidate peers, a given query can be (i) segmented into a set of sub-queries, and (ii) transformed to another query. With respect to the precision performance, our experimentation has shown an improvement of about 42.5% compared to the keyword-based query searching method.     

Robustness Analysis and Enhancement of MANETs Using Human Mobility Traces

Understanding network behavior that undergoes challenges is essential to constructing a resilient and survivable network. Due to the mobility and wireless channel properties, it is more difficult to model and analyze mobile ad hoc networks under various challenges. In this paper, we provide a model to assess the vulnerability of mobile ad hoc networks in face of malicious attacks. We analyze comprehensive graph-theoretical properties and network performance of the dynamic networks under attacks against the critical nodes using real-world mobility traces. Motivated by minimum spanning tree and small-world networks, we propose a network enhancement strategy by adding long-range links. We compare the performance of different enhancement strategies by evaluating a list of robustness measures. Our study provides insights into the design and construction of resilient and survivable mobile ad hoc networks.     

HLLS: A History information based Light Location Service for MANETs

In mobile ad hoc networks, a location service (LS) provides the fundamental service for geographical routing. However, most existing schemes for location service incur a high overhead because of the periodic updates of location information. To address this issue, we propose a novel History information based Light Location Service (HLLS), using the temporal relationship among historical locations of mobile nodes in the network. In HLLS, location information of mobile nodes is propagated by Hello beacons locally, and the location query is performed with the aid of historical locations. In this way, HLLS can eliminate the tremendous periodical location updates and significantly reduce the overhead for location service. Using a combination of analytical modeling and extensive simulations, we show the effectiveness of HLLS in comparison with other approaches.     

异构信息网络的相似性度量方法

随着社交网络和文献索引网络等大规模互联多类异质信息网络的浮现,为相似搜索提出许多挑战,其中相似性度量是关键问题之一。现有适用于同构网络的相似度量方法没有考虑网络多个路径的不同语义。本文提出一种新的基于元路径的相似性度量方法,可以在异构网络中搜索相同类型的对象。元路径是由在不同对象类型中定义的一系列关系所组成的路径,可以为网络中相似搜索引擎提供共同的基础。在真实数据集上的实验表明,与无序相似性衡量方法相比,本文提出的方法支持快速路径相似性查询,可广泛地应用于社交网络和电子商务领域。