Large Scaling Unstructured Peer-to-Peer Networks with Heterogeneity-Aware Topology and Routing

Peer-to-peer (P2P) file sharing systems such as Gnutella have been widely acknowledged as the fastest-growing Internet applications ever. The P2P model has many potential advantages, including high flexibility and serverless management. However, these systems suffer from the well-known performance mismatch between the randomly constructed overlay network topology and the underlying IP-layer topology. This paper proposes to structure the P2P overlay topology using a heterogeneity-aware multitier topology to better balance the load at peers with heterogeneous capacities and to prevent low-capability nodes from throttling the performance of the system. An analytical model is developed to enable the construction and maintenance of heterogeneity-aware overlay topologies with good node connectivity and better load balance. We also develop an efficient routing scheme, called probabilistic selective routing, that further utilizes heterogeneity-awareness to enhance the routing performance. We evaluate our design through simulations. The results show that our multitier topologies alone can provide eight to 10 times improvement in the messaging cost, two to three orders of magnitude improvement in terms of load balancing, and seven to eight times lower topology construction and maintenance costs when compared to Gnutella's random power-law topology. Moreover, our heterogeneity-aware routing scheme provides further improvements on all evaluation metrics, when used with our heterogeneity-aware overlay topologies     

Distributed routing for signal detection in wireless sensor networks

We study the problem of energy-efficient routing for signal detection in wireless sensor networks. Generic routing protocols use networking-centric measures such as minimum hop or minimum energy to establish routes. These schemes do not take into account the performance of application-specific algorithms that is achievable from the data collected by the nodes along the routes. Routing protocols for signal detection have recently been proposed to facilitate joint optimization of detection performance and energy efficiency by developing metrics that connect detection performance with energy consumption of each link along the routes. In existing routing for signal detection (RSD) schemes, however, the routes are computed centrally requiring complex optimization algorithms and global information such as locations and observation coefficients of all nodes in the network. Clearly, for large-scale networks, or networks with dynamically changing topologies, distributed routing schemes are more practical due to their better flexibility and scalability. We present a distributed RSD protocol where each node, based on locally available information, selects its next-hop with the goal of maximizing the detection performance associated with unit energy expenditure. We show that the proposed protocol is readily implementable in ZigBee networks, and present simulation results that reveal its significant improvements in detection performance and energy efficiency over generic routing protocols.     

Prioritized overlay multicast in mobile ad hoc environments

Many proposed routing protocols for manets require nodes to maintain and update complicated route information, which incurs significant overhead when groups have different priorities. To address this problem, some researchers have begun focusing on application-layer, or overlay, multicast in which an overlay network forms a virtual network consisting of only member nodes atop the physical infrastructure. We propose a prototype of prioritized overlay multicast for manets in which participating nodes can carry out multiple functions and thus be associated with more than one overlay tree.     

A scalable P2P overlay based on arrangement graph with minimized overhead

With innovations in the Internet, it is becoming increasingly relied upon. In the last decade, research on peer-to-peer (P2P) technology has become even more popular. As more people use P2P systems, the scalability and flexibility of the systems must be considered. In this study, an arrangement graph is used to form a P2P overlay, the Arrangement-Graph Overlay (AGO), to reduce system overhead and bind routing hops. The proposed AGO utilizes the properties of the arrangement graph, i.e., that each node has a unique ID and IDs between adjacent nodes differ by only one digit, to form the overlay network and develop a routing algorithm. The routing hops of the proposed AGO system can be bound within a certain number because of the diameter of the arrangement graph. Experimental results show that the proposed AGO system can greatly reduce system overhead and perform routing in a constant number of hops, even in a large-scale network environment. The experimental results also show that the AGO system consumes less bandwidth, which is an important consideration in P2P systems.     

Enhancing end-to-end availability and performance via topology-aware overlay networks

This paper proposes a novel overlay architecture to improve availability and performance of end-to-end communication over the Internet. Connectivity and network availability are becoming business-critical resources as the Internet is increasingly utilized as a business necessity. For example, traditional voice and military systems are turning into IP-based network applications. With these applications, even short-lived failures of the Internet infrastructure can generate significant losses.To satisfy these needs, the concept of overlay networks has been widely discussed. However, in the previous studies of overlay networks, a measurable number of path outages were still unavoidable even with use of such overlay networks. We believe that an overlay network’s ability to quickly recover from path outages and congestion is limited unless we ensure path independence at the IP layer. Hence, we develop a simple but effective overlay architecture increasing path independence without degrading performance. The proposed overlay architecture enhances prior studies in the following ways: (1) we deploy overlay nodes considering topology and latency information inside an ISP and also across ISP boundaries; (2) we use a source-based single-hop overlay routing combined with the above topology-aware node deployment; (3) we increase the usage of multi-homing environment at endhosts. In this framework, we develop measurement-based heuristics using extensive data collection from 232 points in 10 ISPs, and 100 PlanetLab nodes. We also validate the proposed framework using real Internet outages to show that our architecture is able to provide a significant amount of resilience to real-world failures.     

基于OLSR协议的无人机自组网多径路由策略

针对现有文献在研究路由协议时选择的路由度量未能结合无人机自组织网络当时的性能水平进而造成路由决策不合理的问题,提出了一种具有负载感知和网络拓扑变动感知能力的多指标多径优化链路状态路由协议（optimized link state routing protocol based on multi-indicator and multi-path,MIMP-OLSR）。该协议首先考虑了无人机场景的节点移动特性和网络的生存时间,并定义了三个用于进行路由选择的指标,即节点的MAC层阻塞度、节点的邻居变化率和节点的多点中继选择节点（multi-point relay selector,MPR_S）邻居数目;其次,结合HELLO和TC两种控制消息提出了一种指标通告机制,用于将指标信息洪泛给全网节点;最后,根据指标信息提出了一种多径路由方案。仿真结果表明,与OLSR、SETT_MPOLSR和UAV-OLSR协议相比,所提协议MIMP-OLSR在成功率、端到端时延和吞吐量性能上均有明显提高,进而证明所提多径路由方案的合理性。     

SCALLOP: a scalable and load-balanced peer-to-peer lookup protocol

A number of structured peer-to-peer (P2P) lookup protocols have been proposed recently. A P2P lookup protocol routes a lookup request to its target node in a P2P distributed system. Existing protocols achieve balanced routing traffic among nodes by assuming that lookup requests are evenly targeted at every node. However, when lookup requests concentrate on a few nodes simultaneously, these nodes become hot spots. Due to uneven routing patterns in existing protocols, hot spots cause unbalanced routing traffic which leads to routing bottlenecks. In this paper, we present a novel structured P2P lookup protocol called SCALLOP that delivers balanced routing and avoids routing bottlenecks at occurrences of hot spots. Among existing protocols, SCALLOP is the first one to accomplish this goal at the fundamental nature of a routing protocol. SCALLOP achieves balanced routing by uniquely constructing a balanced lookup tree for each node. The balanced tree evenly distributes routing traffic among sibling nodes and, therefore, avoids or reduces routing bottlenecks. In addition, as a load-balanced protocol, SCALLOP delivers asymptotically optimal lookup performance at the tradeoff between routing path and routing table size. We conducted a set of simulations to demonstrate the effectiveness of SCALLOP. The results show that, compared-with a most-referenced and representative structured P2P lookup, protocol and a graph-based extension of this protocol, SCALLOP significantly reduces routing bottlenecks while all three protocols deliver comparable lookup performance.     

面向点对点的安全可靠存储系统

利用P2P的方法实现了一个共享和合作的安全存储系统,其中参与节点运行Paramecium协议或其他兼容的DHT(distributed hash table)协议形成自组织覆盖层,维护系统的组织结构和提供路由服务.由于该系统为开放式结构,引入了基于PKI的安全认证机制以确保用户数据的授权访问.用户数据和副本标示的绑定支持了安全的数据自修复;副本类型的引入提供了安全的共享写.初步的分析和实验表明,该P2P系统在现实条件下,在消耗较低的维护带宽的同时维持了较高的可靠性并提供了较好的读写性能.     

LESSON: A system for lecture notes searching and sharing over Internet

In this paper, we present a system LESSON for lecture notes searching and sharing, which is dedicated to both instructors and students for effectively supporting their Web-based teaching and learning activities. The LESSON system employs a metasearch engine for lecture notes searching from Web and a peer-to-peer (P2P) overlay network for lecture notes sharing among the users. A metasearch engine provides an unified access to multiple existing component search engines and has better performance than general-purpose search engines. With the help of a P2P overlay network, all computers used by instructors and students can be connected into a virtual society over the Internet and communicate directly with each other for lecture notes sharing, without any centralized server and manipulation. In order to merge results from multiple component search engines into a single ranked list, we design the RSF strategy that takes rank, similarity and features of lecture notes into account. To implement query routing decision for effectively supporting lecture notes sharing, we propose a novel query routing mechanism. Experimental results indicate that the LESSON system has better performance in lecture notes searching from Web than some popular general-purpose search engines and some existing metasearch schemes; while processing queries within the system, it outperforms some typical routing methods. Concretely, it can achieve relatively high query hit rate with low bandwidth consumption in different types of network topologies.     

基于位置信息的改进AODV路由算法

针对AODV协议路由开销较大的问题,提出一种基于位置信息的改进路由协议(GAODV).GAODV利用中间节点重新计算转发角度,保证转发角度内邻居节点数不小于预设门限值,同时还引入基于位置信息的计数器方案,使距离目的节点近的中间节点优先转发路由请求消息,有利于减少转发冗余路由请求信息和降低寻路失败概率.OPNET仿真实验结果表明,GAODV在数据分组投递率、路由开销、总丢包数、端到端时延和平均路由跳数等方面都优于已有算法.     

Utilizing correlated node mobility for efficient DTN routing

In a delay tolerant network (DTN), nodes are connected intermittently and the future node connections are mostly not known. Therefore, effective forwarding based on limited knowledge of contact behavior of nodes is challenging. Most of the previous studies assumed that mobility of a node is independent from mobility of other nodes and looked at only the pairwise node relations to decide routing. In contrast, in this paper, we analyze the temporal correlation between the meetings of each node with other nodes and utilize this correlation for efficient routing. We introduce a new metric called conditional intermeeting time (CIT), which computes the average intermeeting time between two nodes relative to a meeting with a third node. Then, we modify existing DTN routing protocols using the proposed metric to improve their performance. Extensive simulations based on real and synthetic DTN traces show that the modified algorithms perform better than the original ones.     

覆盖多播路由的算法及协议研究综述

虽然IP多播的性能优势无可否认,但是它却面临着部署上的困难。近年来,覆盖多播作为提供多播服务的另一可行途径正不断为人们所认可。本文对覆盖多播路由的算法和协议进行了综述研究,提出了通用的覆盖多播网络模型,对覆盖多播中的路由优化问题进行了分类。在此基础上,介绍了当前重要的覆盖多播路由算法和协议,并对它们的性能参数、所解决的路由问题、系统结构和控制方式等技术特点进行了全面的分析和讨论。另外,本文还指出了覆盖多播路由中一些有待进一步研究的问题。     

一种负载感知的结构化P2P协议

提出并建立一种负载感知的结构化P2P协议——LaChord,采用负载感知的被动式路由表维护机制和负载感知的路由算法,通过增加轻载节点的入度来增大轻载节点作为路由中继节点的概率,在保证查询性能的前提下使消息路由到轻载节点。实验表明,与没有采用负载感知的协议相比,采用负载感知的结构化P2P协议可使系统内节点负载达到更好的平衡,负载感知的算法有助于提高系统的扩展性能。     

基于分类节点的P2P语义路由模型

对于P2P语义覆盖网络,语义信息的维护和智能路径的选择是实现的难点。根据小世界原理,提出了一种新的基于节点分类划分的P2P语义路由模型。通过建立节点本体来描述节点的网络结构和节点下的内容项,在此基础上创建了路由消息格式和节点分类划分的方法,然后创建了支持内容语义查询的节点内相关性内容查询算法和节点间消息路由算法。通过实验对比,该语义路由模型能够提高P2P系统下的内容查找速度并且能够显著降低占用的网络带宽。     

Constructing rings overlay for robust data collection in wireless sensor networks

This paper investigates the construction of rings overlay in wireless sensor networks and presents an enhanced relay scheme for improving the robustness of data collection through the rings overlay. Rings overlay is a class of multi-path routing structure that exploits the broadcast nature of wireless communication to cope with communication failures. In constructing the rings overlay, we propose a distributed approach to allow sensor nodes to benefit from multi-path routing as much as possible. Our proposed approach only requires sensor nodes to have local neighborhood information. In our enhanced relay scheme, sensor nodes in the ring next to the base station benefit from multi-path routing without having to transmit their data multiple times. Experimental results show that compared with a baseline greedy construction approach and the original relay scheme, the proposed techniques of overlay construction and relay enhancement significantly improve the robustness and accuracy of sensor data collection through the rings overlay.     

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。     

大规模MANET路由协议SPDSR的仿真研究

为改善大规模自组织网络中的通信质量,介绍了一种基于P2P(peer-to-peer,P2P)计算模式的新型MANET路由模型——SPDSR (structured peer computing based dynamic source routing)[1].根据移动自组网和对等网络的特点,对结构化P2P覆盖层网络技术应用到移动自组织网络路由中的可行性及原理进行了说明,在此基础上设计实现了该算法.最后通过NS2仿真工具对新协议进行了仿真,并与其他协议进行比较.实验结果表明,新协议在大规模网络中的性能优于其它协议,具有较强的可扩展性,研究结果为改善大规模网络的通信质量提供了可行的解决方案.     

基于幂律分布的结构化P2P覆盖网

利用无标度网络的幂律分布特性对结构化P2P覆盖网进行改进,提出基于幂律分布的BAChord模型,利用节点的连接度和物理邻接度的信息,使覆盖网与物理拓扑结构之间能够达到一定程度的匹配,增加路由过程中发现连接短链的概率。实验证明,该模型能在增加少量路由开销的情况下,达到比Chord模型更好的路由性能。     

Achieving effective resilience for QoS-aware application mapping

Overlay mapping provides a flexible and effective means of application deployment by selecting a subset of nodes and links from the substrate-hosting network to meet, or even enhance, the requirements of the application. In order to take full advantage of the potential of overlay mapping given the features of the substrate network, such as topology and performance characteristics, it is critical to carefully choose the subset of hosting nodes. This is to balance the effectiveness of the overlay mapping with substrate network constraints and resource usage. In this paper, we investigate how to provide effective resilience for a QoS-aware overlay mapping so as to make the mapped applications resilient against substrate network failure(s) whilst providing enhanced QoS. We first formulate the problem as an Integer Linear Program (ILP). Using simulations with small networks, existing methods are shown to be capable of achieving enhanced QoS but lack effective resilience when compared against the optimal ILP solution. To address this issue, a novel heuristic is proposed which incorporates substrate topology information. Through simulations with synthetic and real networks, the effectiveness of the new heuristic is confirmed.