A scalable P2P platform for the knowledge grid

The knowledge grid needs to operate with a scalable platform to provide large-scale intelligent services. A key function of such a platform is to efficiently support various complex queries in a dynamic large-scale network environment. This paper proposes a platform to support index-based path queries by incorporating a semantic overlay with an underlying structured P2P network that provides object location and management services. Various distributed indexing structures can be dynamically formed by publishing, semantic objects as indexing nodes. Queries are forwarded along the chains of semantic object pointers to search for objects. We investigate the deployment of a scalable distributed trie index for broadcast queries on key strings, propose a decentralized load balancing method for solving the problem of uneven load distribution incurred by heterogeneity of loads and node capacities and by the distributed trie index, and give an approach for improving the availability of the semantic overlay and its trie index. Experiments demonstrate the scalability of the proposed platform.     

Building a network-aware and load-balanced peer-to-peer system for range queries

We present a structured P2P system called Donuts for range queries, which takes two important yet somewhat conflicting issues into account: proximity and load balance. Proximity allows physically close nodes to be arranged near each other in the overlay so as to reduce the cost of neighbor communications that occur quite often in a range-queriable system. Load balance is crucial because object distribution in a semantically meaningful key space is often skewed. Efficient load balance, however, requires flexible node position in the overlay, and thus conflicts with proximity.Donuts resolves the problem by separating physically close nodes into several overlay sections. By dynamically switching between these sections, they help one another balance their loads without altering overlay proximity too much. Still, breaking apart physically close nodes inevitably compromises overlay proximity. Therefore, we have put much effort in the overlay construction to ensure that load balance can be performed effectively and efficiently, with minimal damage to overlay proximity.     

Locality in structured peer-to-peer networks

Distributed hash tables (DHTs), used in a number of structured peer-to-peer (P2P) systems, provide efficient mechanisms for resource placement and location. A key distinguishing feature of current DHT systems, such as Chord, Pastry, CAN and Tapestry, is the way they handle locality in the underlying network. Topology-based node identifier assignment, proximity routing, and proximity neighbor selection are examples of heuristics used to minimize message delays in the underlying network. While these heuristics are sometimes effective, they all rely on a single global overlay that may install the key of a popular object at a node far from most of the nodes accessing it. Furthermore, a response to a lookup message does not contain any locality information about the nodes holding a copy of the object. We address these issues in Plethora, a novel two-level overlay P2P network. A local overlay in Plethora acts as a locality-aware cache for the global overlay, grouping nodes close together in the underlying network. Local overlays are constructed by exploiting the organization of the Internet into autonomous systems (ASs). We present a detailed experimental study that demonstrates performance gains in response time of up to 60% compared to a single global Pastry overlay. We also present efficient distributed algorithms for maintaining local overlays in the presence of node arrivals and departures.     

基于校园环境的移动P2P网络体系研究与设计

由于P2P技术的广泛应用以及无线网络和移动设备的普及,人们提出了基于无线网络的移动P2P网络。文中通过分析移动P2P网络的特点和已有的网络模型,结合校园网络环境的特点,设计出基于校园环境的网络体系结构模型,并对模型的资源查找进行详细的描述。模型被划分成三层结构,底层的网络采用改进后的Kelips路由算法通信,该算法的路由复杂度是一个常数,有效减少资源查找时间,保证节点维护状态信息的实时性和正确性;由超级节点组成的中间层,实行分布式管理,采取泛洪搜索算法来通信;顶层是一些域内中心节点,负责连接外网和解决网络的安全问题。仿真实验表明：该模型能够更好地减少资源查找时间,即使大量节点失效,也可以快速检测到节点间关系变化并进行管理。     

Load Balanced Mapping of Distributed Objects to Minimize Network Communication

This paper introduces a new load balancing and communication minimizing heuristic used in theInverse Remote Procedure Call(IRPC) system. While the paper briefly describes the IRPC system, the focus is on the newIRPCassignment heuristic. The IRPC compiler maps a distributed program to a graph that represents program objects and their dependencies (due to invocations and parameter passing) as nodes and edges, respectively. In the graph, the system preserves conditional and iterative flows, records network transmission and execution costs, and marks nodes that have to reside at specific network sites. The graph is then partitioned by the heuristic to derive a (sub)optimal node assignment to network sites minimizing load balancing and network data transport. The resulting program partition is then reflected in the physical object distribution, and remote and local object communication is transparently implemented. The compiler and run-time system use efficient implementation techniques such as type prediction, inlining, splitting and subprogram passing. The last of these allows remote code to be copied to local data, as an alternative to copying data to the remote site, whenever this will reduce network data transport. The IRPC graph partitioning heuristic operates in timeO(E(logd+l+ logM)), whereMis the number of network sites,Eis the number of communication edges, anddis the maximum degree of a node;lis a parameter of the algorithm, and can vary between 1 andN, whereNis the number of communicating objects. This complexity is more nearly independent ofM, and considerably better in terms ofEandN, than that of previously known related algorithms, such as A*, which employs backtracking and is potentially exponential, or the max-flow/min-cut class of network flow algorithms or heuristics which tend to be at least of Ω(MN²E), and it can be made (by choosinglappropriately) as efficient as even such fast heuristics as heaviest-edge-first, minimal communication, and Kernighan–Lin. In an extensive quantitative evaluation, the heuristic has been demonstrated to perform very well, giving on the average 75% traffic cost reductions for over 95% of the programs when compared to random partitioning, and outperforming in cost reduction and actual execution time the three aforementioned fast heuristics, even with a largel. Thus, to the best of our knowledge, this is the first report of a well-performing assignment heuristic that is bothessentially linearin the number of communication edges, andbetterthan existing, established heuristics of no better complexity.     

无线传感器网络中一种基于接收功率异常的入侵检测算法

虽然静态传感器节点计算能力和通信能力较差,但是它们具有自己独特的特征,可以获取比较稳定的临域节点信息.利用这个特征可以检测网络异常情况以及临域节点的通信行为,为传感器网络提供安全保障.为了使传感器节点能够检测出入侵者,需要先建立一种简单的基于临域节点的动态统计模型,然后用一种低复杂度的检测算法监测已接收到的数据包的接收功率.首先介绍了一种基于无线传感器网络安全的入侵检测算法,然后介绍了一种基于该算法的节点协作检测技术,节点协作指的是对攻击的联合确认,以及邻居节点共同反抗入侵者的协作行为.     

HRing: A Structured P2P Overlay Based on Harmonic Series

This paper presents Harmonic Ring (HRing), a structured peer-to-peer (P2P) overlay where long links are built along the ring with decreasing probabilities coinciding with the Harmonic Series. HRing constructs routing tables based on the distance between node positions instead of node IDs in order to eliminate the effect of node ID distribution on the long link distribution and load balance. It supports leave-and-rejoin load balance without incurring uneven long link distribution. In addition, node IDs can be any form, like number, string, address, and date, without the prerequisite of uniform distribution, so they can preserve the semantics and range locality of data objects. HRing supports multidimensional range queries. Each node is expected to have O(ln(n)) long links. The construction of O(ln(n)) long links for a node costs (O(ln(n)) messages. Routing queries achieve O(ln(n)) hops. Analyses and simulations demonstrate the efficiency of query routing and the effectiveness of the long link construction method.     

Performance evaluation of immunity-based statistical en-route filtering in wireless sensor networks

Statistical en-route filtering (SEF) schemes can detect and eliminate false data injection attacks in wireless sensor networks. However, SEF does not address the identification of the compromised nodes which are injecting false reports. Therefore, we have proposed an immunity-based SEF to identify compromised nodes and achieve earlier detection of false reports. In the proposed scheme, each node has a list of neighborhood nodes and assigns credibility to each neighboring node. Each node can update the credibility of a neighboring node based on the success or failure of filtering and communication, and can then use the updated credibility as the probability of the next communication. In this article, some simulation results show that the immunity-based SEF outperforms the original SEF.     

根据IP地址奇偶性优化P2P对等网的方法

针对对等网(P2P)中因抽象的覆盖网与底层物理网不匹配而在网络上产生了大量多余的传送开销的问题,提出了一种基于IP地址奇偶性的方案来优化对等网的拓扑结构。该方法根据IP地址的奇偶性将对等网中的结点分成两组完成不同的工作。模拟实验证明了这种方法没有缩减查询范围,同时减小了网络中的传输负载和结点的工作负载,缩短了查询的响应时间,有效地解决了覆盖网与底层物理网拓扑不匹配现象。     

Fast and proximity-aware multi-source overlay multicast under heterogeneous environment

Overlay multicast has been considered as one of the most important developments for the next generation Internet infrastructure. In this paper, we consider overlay multicast in the scenarios where any participant node is a potential data source. Existing multicast algorithms for single-source always require a long time to deliver messages or have high maintenance overhead when multiple data sources are allowed. There are other algorithms that are designed for multi-source scenarios. But they consume too much network resources and have a long convergence time because of proximity ignorance. To address the issues, we present FPCast, which leverages node heterogeneity and proximity information at the same time. Physically close nodes are grouped into clusters and each cluster selects a powerful, stable node as its rendezvous point. The rendezvous nodes form a DHT-based structure. Data messages are replicated and forwarded along implicit, source specific, and heterogeneity-aware multicast trees. We further reduce the delivery delay by introducing probabilistic forwarding scheme. We show the average delivery path length converges to O(logn) automatically (n is the number of nodes in the overlay). The simulation results demonstrate the superiority of our algorithm in terms of message delivery time and network resource consumption, in comparison with the previous randomized algorithms. The algorithm is also resilient to node failures.     

TR-clustering: Alleviating the impact of false clustering on P2P overlay networks

Designing topologically-aware overlays is a recurrent subject in peer-to-peer research. Although there exists a plethora of approaches, Internet coordinate systems such as GNP (which attempt to predict the pair-wise O(N²) latencies between N nodes using only O(N) measurements) have become the most attractive approach to make the overlay connectivity structures congruent with the underlying IP-level network topology. With appropriate input, coordinate systems allow complex distributed problems to be solved geometrically, including multicast, server selection, etc. For these applications, and presumably others like that, exact topological information is not required and it is sufficient to use informative hints about the relative positions of Internet clients. Clustering operation, which attempts to partition a set of objects into several subsets that are distinguishable under some criterion of similarity, could significantly ease these operations. However, when the main objective is clustering nodes, Internet coordinate systems present strong limitations to identify the right clusters, a problem known as false clustering.In this work, the authors answer a fundamental question that has been obscured in proximity techniques so far: how often false clustering happens in reality and how much this affects the overall performance of an overlay. To that effect, the authors present a novel approach called TR-Clustering to cluster nodes in overlay networks based on their physical positions on the Internet. To be specific, TR-Clustering uses the Internet routers with high vertex betweenness centrality to cluster participating nodes. Informally, the betweenness centrality of a router is defined as the fraction of shortest paths between all pairs of nodes running through it. Simulation results illustrate that TR-Clustering is superior to existing techniques, with less than a 5% of falsely clustered peers (of course, relative to the datasets utilized in their evaluation).     

一种基于P2P的流媒体分发系统

利用P2P思想,在应用层设计一个覆盖网络,网络内部以频道分簇,簇内节点以树形组织。描述了节点间管理协议。在父节点选择算法中,综合考虑了节点间的距离、节点在线时长、负载状况、与根节点的跳数等因素。最后,通过分析对比,说明该系统具有较低的数据传输延迟、较好的稳定性和鲁棒性。     

负载敏感的P2P覆盖网

P2P网络较好地实现了大范围分布式环境下的节点自组织,但面向实际应用时,由于节点能力的差异带来了负载均衡问题.按照混合层次网络架构,基于Treap树设计了一种P2P覆盖网,根据负载率的优先级构造最小堆,并动态维护,实现稳定化操作.节点通过Treap树的信息汇聚机制获取后代节点的负载率,以此为基础实现负载均衡策略.仿真结...     

On graph-based characteristics of optimal overlay topologies

In this paper, we address the challenge of overlay topology design by considering which overlay topology best minimizes cost function, taking into account overlay link creation cost and routing cost. First, we formulate the problem as Integer Linear Programming (ILP) given a traffic matrix and assuming cooperative behavior of nodes. Then, we propose some heuristics to find near-optimal overlay topologies with a reduced complexity. The solutions to the ILP problem on real network topologies have been analyzed, showing that the traffic demands between the nodes affect the decision to create new overlay links. Next, the obtained optimal and near-optimal overlay topologies are thoroughly analyzed and the heuristics are compared through extensive numerical evaluations. Finally guidelines for the selection of the best heuristic as a function of the cost parameters are also provided.     

Load balancing in peer-to-peer systems using a diffusive approach

We developed a diffusive load balancing technique for P2P systems. This technique uses the overlay network of a P2P system and results in the nodes of the network having similar available capacities; therefore the services hosted on these nodes are expected to have similar mean response times. In this paper, the technique is presented, including the policies, stages of operation, and decision algorithms. The convergence of the available capacities to the global average is demonstrated. The convergence speed depends on the decision algorithm, the neighborhood structure of the underlying overlay network, and the workload distribution. When used in a system with churn, the technique keeps the standard deviation of available capacities in the system within a bound. This bound depends on the amount of churn and the frequency of the load balancing operations, as well as on the distribution of node capacities. However, the sizes of services have little impact on this bound. The paper presents the results of analytical analysis and simulation studies.     

Toward Optimal Network Fault Correction in Externally Managed Overlay Networks

We consider an end-to-end approach of inferring probabilistic data forwarding failures in an externally managed overlay network, where overlay nodes are independently operated by various administrative domains. Our optimization goal is to minimize the expected cost of correcting (i.e., diagnosing and repairing) all faulty overlay nodes that cannot properly deliver data. Instead of first checking the most likely faulty nodes as in conventional fault localization problems, we prove that an optimal strategy should start with checking one of the candidate nodes, which are identified based on a potential function that we develop. We propose several efficient heuristics for inferring the best node to be checked in large-scale networks. By extensive simulation, we show that we can infer the best node in at least 95 percent of time, and that first checking the candidate nodes rather than the most likely faulty nodes can decrease the checking cost of correcting all faulty nodes.     

HD Tree: A novel data structure to support multi-dimensional range query for P2P networks

There are two basic concerns for supporting multi-dimensional range query in P2P overlay networks. The first is to preserve data locality in the process of data space partitioning, and the second is the maintenance of data locality among data ranges with an exponentially expanding and extending rate. The first problem has been well addressed by using recursive decomposition schemes, such as Quad-tree, K-d tree, Z-order, and Hilbert curve. On the other hand, the second problem has been recently identified by our novel data structure: HD Tree. In this paper, we explore how data locality can be easily maintained, and how range query can be efficiently supported in HD Tree. This is done by introducing two basic routing strategies: hierarchical routing and distributed routing. Although hierarchical routing can be applied to any two nodes in the P2P system, it generates high volume traffic toward nodes near the root, and has very limited options to cope with node failure. On the other hand, distributed routing concerns source and destination pairs only at the same depth, but traffic load is bound to some nodes at two neighboring depths, and multiple options can be found to redirect a routing request. Because HD Tree supports multiple routes between any two nodes in the P2P system, routing in HD Tree is very flexible; it can be designed for many purposes, like fault tolerance, or dynamic load balancing. Distributed routing oriented combined routing (DROCR) algorithm is one such routing strategy implemented so far. It is a hybrid algorithm combining advantages from both hierarchical routing and distributed routing. The experimental results show that DROCR algorithm achieves considerable performance gain over the equivalent tree routing at the highest depth examined. For supporting multi-dimensional range query, the experimental results indicate that the exponentially expanding and extending rate have been effectively controlled and minimized by HD Tree overlay structure and DROCR routing.     

自组织覆盖网络QoS组播动态路由优化研究

针对覆盖组播节点的动态特性,研究自组织覆盖网络带度和延时约束的组播动态路由问题,提出了动态覆盖组播路由算法AHMQ。组播树由目的节点驱动动态渐近形成,动态路由优化在通信过程中进行。协议是软状态的,仅要求节点维护局部状态信息,同时利用覆盖网络技术和无线媒质的广播能力,降低了网络负载,提高了重构能力。对算法进行了分析研究,通过实验验证了该算法具有较好的性能。     

ACOM: Any-source Capacity-constrained Overlay Multicast in Non-DHT P2P Networks

rdquoApplication-level multicast is a promising alternative to IP multicast due to its independence from the IP routing infrastructure and its flexibility in constructing the delivery trees. The existing overlay multicast systems either support a single data source or have high maintenance overhead when multiple sources are allowed. They are inefficient for applications that require any-source multicast with varied host capacities and dynamic membership. This paper proposes ACOM, an any-source capacity-constrained overlay multicast system, consisting of three distributed multicast algorithms on top of a non-DHT overlay network with simple structures (random overlay with a non-DHT ring) that are easy to manage as nodes join and depart. The nodes have different capacities, and they can support different numbers of direct children during a multicast session. No explicit multicast trees are maintained on top of the overlay. The distributed execution of the algorithms naturally defines an implicit, roughly balanced, capacity-constrained multicast tree for each source node. We prove that the system can deliver a multicast message from any source to all nodes in expected O(log_c n) hops, which is asymptotically optimal, where c is the average node capacity and n is the number of members in a multicast group.     

基于移动机器人的无线传感器网络数据收集方法

稀疏无线传感器网络中各传感器节点距离较远,而传统的静态数据收集方法要求各传感器节点直接通信,导致网络延迟时间长,能耗高。针对该问题,提出一种基于移动机器人的无线传感器数据收集方法。该方法首先由静态节点选择与路径最短的移动机器人作为簇头,移动机器人比较一定周期内检测到的邻居节点的平均剩余能量与整个网络传感器节点平均剩余能量,根据比较结果决定其是否移动,若移动则采用范围可控的随机移动策略;当移动机器人移动到新位置时,传感器节点更新路由,选择新的移动机器人作为簇头。仿真结果表明,与传统的静态无线传感器网络数据收集方法相比,基于移动机器人的无线传感器网络数据收集方法大大降低了数据传输延迟和节点能量消耗。