Performance evaluation of a Kademlia-based communication-oriented P2P system under churn

The phenomenon of churn has a significant effect on the performance of Peer-to-Peer (P2P) networks, especially in mobile environments that are characterized by intermittent connections and unguaranteed network bandwidths. A number of proposals have been put forward to deal with this problem; however, we have so far not seen any thorough analysis to guide the optimal design choices and parameter configurations for structured P2P networks. In this article, we present a performance evaluation of a structured communication-oriented P2P system in the presence of churn. The evaluation is conducted using both simulation models and a real-life prototype implementation. In both evaluation environments, we utilize Kademlia with some modifications as the underlying distributed hash table (DHT) algorithm, and Peer-to-Peer Protocol (P2PP) as the signaling protocol. The results from the simulation models created using Nethawk EAST (a telecommunication simulator software) suggest that, in most situations, a lookup parallelism degree of 3 and resource replication degree of 3 are enough for guaranteeing a high resource lookup success ratio. We also notice that, with the parallel lookup mechanism, a good success ratio is achieved even without the KeepAlive traffic that is used for detecting the aliveness of nodes. A prototype system that works in mobile environment is implemented to evaluate the feasibility of mobile nodes acting as full-fledged peers. The measurements made using the prototype show that, from the viewpoints of CPU load and network traffic load, it is feasible for the mobile nodes to take part in the overlay. Through energy consumption measurements, we draw the conclusion that in general the UMTS access mode consumes slightly more power than the WLAN access mode. Protocol packets with sizes of 200 bytes or less are observed to be the most energy efficient in the UMTS access mode.     

异构移动终端能量感知的P2P数据共享机制

针对现有P2P数据共享网络中存在的移动终端异构性这一问题,提出一种异构移动终端能量感知的P2P数据共享机制。该机制在判断移动终端类型的同时引入能量感知模块,用于预测终端的剩余能量,在此基础上,根据网络环境的变化动态地调整数据的共享策略。仿真实验表明,该机制能够有效提高移动终端的能量利用率,平衡终端的负载,延长数据共享时间,从而提高数据分发成功率。在保持文件高可用性的前提下,平均减少15%的终端能耗。     

一种用于大规模P2P点播系统的拓扑结构

提出了一种基于动态时间坐标的分层DHT拓扑结构,解决了因大规模P2P点播系统要求细粒度追踪而难以应用DHT的问题。在动态时间坐标系中,节点的播放点坐标不再随着节点的播放而移动,从而使得DHT能够用于追踪点播系统节点缓存位置。仿真结果证明了方法的有效性。     

基于IPv6、簇和超节点的P2P路由模型研究

针对当前P2P网络模型存在逻辑拓扑与物理拓扑失配和没有充分考虑节点异构性的缺点,利用IPv6特有的层次化地理布局,实现逻辑拓扑与物理拓扑的有效结合,应用簇减少节点频繁加入和退出所带来的网络抖动问题,充分考虑节点之间的性能差异,让性能好的节点承担更多的任务,利用节点成功的资源访问记录进一步提高路由效率。通过模拟实验和对相关数据的分析,证明该项研究能使路由延迟减少,网络更稳定,更易于管理和维护。     

基于拥塞控制的非结构化P2P网络的路由负载均衡策略

非结构化P2P(unstructured peer-to-peer network)对等网络中的节点资源定位的路由查询是对等网络研究中的一个主要难题,特别是当网络中客户端节点由于其频繁加入、离开导致网络结构动态变化所带来的资源查询难题.提出了一种新的基于拥塞控制的路由查询方法来实现动态网络下的资源查询.该方法分两部分实现:首先是网络资源的分组与节点重连策略.该策略使得具有同等资源的节点相互连接,并周期性地调整节点上的节点连接数量以减少同组资源节点上的负载.通过以上策略,使得网络的拓扑结构自动地从随机网络结构进化到以资源组为单位的聚类网络,从而使得网络中形成网络资源组间的查询负载均衡.另一方面,组内的节点之间的路由负载均衡是通过节点间协同学习实现的.采用协同Q-学习方法,所研究的方法不仅从节点上学习其处理能力、连接数和资源的个数等参数,还将节点的拥塞状态作为协同Q-学习的重要参数,并建立模型.通过这种技术,同一组节点上的资源查询被有目的地引导,以避开那些组内拥塞的节点,从而最终实现资源组内节点之间的查询均衡.仿真实验结果表明,相比常用的random walk资源查找方法,该研究所实现的资源定位方法能够更迅速地实现网络的资源查询.仿真结果还表明,相比random walk方法,所提出的方法在网络高强度查询和网络节点动态加入和退出的情况下进行查询具有更高的鲁棒性和适应性.     

Performance analysis of structured peer-to-peer overlays for mobile networks

Distributed Hash Table (DHT) based Peer-to-Peer (P2P) overlays have been widely researched and deployed in many applications such as file sharing, IP telephony, content distribution and media streaming applications. However, their deployment has largely been restricted to fixed, wired networks. This is due to the fact that supporting P2P overlays on wireless networks such as the public mobile data network is more challenging due to constraints in terms of data transmissions on cellular networks, limited battery power of the handsets and increased levels of node churn. However, the proliferation of smartphones makes the use of P2P applications on mobile handsets very desirable. In this article, we have analysed and evaluated the performance and efficiency of five popular DHT based structured P2P overlays (Chord, Pastry, Kademlia, Broose and EpiChord) under conditions as commonly experienced in public mobile data networks. Our results show that the conditions in mobile networks, including a high churn rate and the relatively low bandwidth availability is best matched by Kademlia and EpiChord. These overlays exhibit a high lookup success ratio and low hop count while consuming a moderate amount of bandwidth. These characteristics make these two overlays suitable candidates for use in mobile networks.     

Application of a JXTA-overlay P2P system for end-device control and e-learning

This work is motivated by the need to develop decentralized P2P approaches for controlling end-devices in a wide-area network without changing the network security policy. Much of current research work on P2P systems is devoted to P2P networks of standard peers such as PCs. Due to improvements of connections capabilities of mobile devices and end-devices, there is an increasing interest to design, implement and deploy full featured P2P networks that integrate standard peers, mobile devices and end-devices. In this paper, we use the JXTA-Overlay for the control of end-devices and e-learning in a P2P network. We considered as end-devices the smart box (which is used for stimulating the learners in our implemented P2P e-learning system), robot, and room lightening. We also considered the control of a mobile car in order to prove the applicability of our approach in wireless environment. The proposed approach, due to the capabilities of JXTA protocols to overcome firewalls and NATs, is able to control devices without changing network security policies. We evaluate the proposed system by many experiments and have shown that the proposed system has a good performance and can be used successfully for the control of end-devices and in e-learning.     

P2P-Grid环境中基于流言传播的资源查找方法研究

对两层结构的 P2P-Crid 网格模型进行了改进,在超级节点层上增加了分类节点层,即选择超级节点中性能较高的节点存放分类信息.给出了基于流言传播机制的分布式资源查找算法,该算法利用流言传播机制具有传播流言的兴趣随着重复收到某个流言而减少的特点,避免某个节点处理查找信息的负载过大,实现负载平衡,并与传统的泛洪算法进行了比较.模拟实验证明该算法能够缩短资源请求的响应时间,并且减少网格通信开销.     

Evaluating and improving the content access in KAD

We analyze in detail the content retrieval process in kad. kad implements content search (publish and retrieval) functions that use the Kademlia Distributed Hash Table for content routing. Node churn is quite common in peer-to-peer systems and results in information loss and stale routing table entries. To deal with node churn, kad issues parallel route requests and publishes multiple redundant copies of each piece of information. We identify the key design parameters in kad and present an analytical model to evaluate the impact of changes in the values of these parameters on the overall lookup latency and message overhead. Extensive measurements of the lookup performance using an instrumented client allow us to validate the model. The overall lookup latency is in most cases 5 s or larger. We elucidate the cause for such high lookup latencies and propose an improved scheme that significantly decreases the overall lookup latency without increasing the overhead.     

Topological Implications of Selfish Neighbor Selection in Unstructured Peer-to-Peer Networks

Current peer-to-peer (P2P) systems often suffer from a large fraction of freeriders not contributing any resources to the network. Various mechanisms have been designed to overcome this problem. However, the selfish behavior of peers has aspects which go beyond resource sharing. This paper studies the effects on the topology of a P2P network if peers selfishly select the peers to connect to. In our model, a peer exploits locality properties in order to minimize the latency (or response times) of its lookup operations. At the same time, the peer aims at not having to maintain links to too many other peers in the system. By giving tight bounds on the price of anarchy, we show that the resulting topologies can be much worse than if peers collaborated. Moreover, the network may never stabilize, even in the absence of churn. Finally, we establish the complexity of Nash equilibria in our game theoretic model of P2P networks. Specifically, we prove that it is NP-hard to decide whether our game has a Nash equilibrium and can stabilize.     

Hierarchically Clustered P2P Video Streaming: Design,implementation, and evaluation

P2P based live streaming has been gaining popularity. The new generation P2P live streaming systems not only attract a large number of viewers, but also support better video quality by streaming the content at higher bit-rate. In this paper, we propose a novel P2P streaming framework, called Hierarchically Clustered P2P Video Streaming, or HCPS, that can support the streaming rate approaching the optimal upper bound while accommodating large viewer population. The scalability comes with the hierarchical overlay architecture by grouping peers into clusters and forming a hierarchy among them. Peers are assigned to appropriate cluster so as to balance the bandwidth resources across clusters and maximize the supportable streaming rate. Furthermore, individual peers perform distributed queue-based scheduling algorithms to determine how to retrieve data chunks from source and neighboring peers, and how to utilize its uplink bandwidth to serve data chunks to other peers. We show that queue-based scheduling algorithms allow to fully utilize peers’ uplink bandwidths, and HCPS supports the streaming rate close to the optimum in practical network environment. The prototype of HCPS is implemented and various design issues/tradeoffs are investigated. Experiments over the PlanetLab further demonstrate the effectiveness of HCPS design.     

一种有效的簇集主干点P2P网络结构模型

文中提出一种有效的簇集主干点P2P网络结构模型，克服了非结构化P2P系统中存在的扩展性不好和搜索效率不高的问题。该模型根据拓扑优先级把对等点聚类成簇形层级结构，从CN中选出GN充当簇的中心和服务提供者，实现定位查询和信息交互。为了衡量由主干点组成的骨干网的路由，文中设计了一种适用于应用级广播协议的路由算法。实验利用Java平台和仿真工具模拟实时网络环境，比较层级结构结合主干点骨干协议的系统模型和Gnuteua系统的代价。实验结果证明这种层级结构的簇集P2P模型，加上骨干网协议支持，在系统性能和可扩展性上带来了明显地提升，并可在大范围非结构化的P2P环境中得到应用推广。     

Affinity P2P: A self-organizing content-based locality-aware collaborative peer-to-peer network

The last years have brought a dramatic increase in the popularity of collaborative Web 2.0 sites. According to recent evaluations, this phenomenon accounts for a large share of Internet traffic and significantly augments the load on the end-servers of Web 2.0 sites. In this paper, we show how collaborative classifications extracted from Web 2.0-like sites can be leveraged in the design of a self-organizing peer-to-peer network in order to distribute data in a scalable manner while preserving a high-content locality. We propose Affinity P2P (AP2P), a novel cluster-based locality-aware self-organizing peer-to-peer network. AP2P self-organizes in order to improve content locality using a novel affinity-based metric for estimating the distance between clusters of nodes sharing similar content. Searches in AP2P are directed to the cluster of interests, where a logarithmic-time parallel flooding algorithm provides high recall, low latency, and low communication overhead. The order of clusters is periodically changed using a greedy cluster placement algorithm, which reorganizes clusters based on affinity in order to increase the locality of related content. The experimental and analytical results demonstrate that the locality-aware cluster-based organization of content offers substantial benefits, achieving an average latency improvement of 45%, and up to 12% increase in search recall.     

基于P2P的流媒体直播技术研究与展望

覆盖网络的组织与维护对于P2P流媒体直播系统的性能有着极其重要的影响.根据覆盖网络拓扑组织形式的不同,分别研究了基于单树结构、多树结构、随机拓扑结构的现有P2P流媒体直播技术方案,并结合节点的动态行为和传输延迟对方案的优缺点进行了分析比较.以此为基础概括总结有待解决的主要问题,展望了未来的研究方向,为基于P2P流媒体直播的进一步的研究和应用提供有益的参考.     

基于P2P的分布式多媒体服务

在两个层次的P2P网络中,利用组间复制算法将多媒体内容复制到各个组中,改善分布效率;组内复制算法将多媒体内容复制到Peer中,提高内容的可用性。模拟显示本系统的时延比FreeNet网络小20%,比随机复制系统小50%,能提供更好的视频服务质量,该方法是分布式、可扩展、高效的。     

Building a peer-to-peer content distribution network with high performance,scalability and robustness

Content distribution networks (CDN) are fundamental, yet expensive technologies for distributing the content of web-servers to large audiences. The P2P model is a perfect match to build a low-cost and scalable CDN infrastructure for popular websites by exploiting the underutilized resources of their user communities. However, building a P2P-based CDN is not a straightforward endeavor. In contrast to traditional CDNs, peers are autonomous and volunteer participants with their own heterogeneous interests that should be taken into account in the design of the P2P system. Moreover, churn rate is much higher than in dedicated CDN infrastructures, which can easily destabilize the system and severely degrade the performance. Finally and foremostly, while many P2P systems abstract any topological information about the underlying network, a top priority of a CDN is to incorporate locality-awareness in query routing in order to locate close-by content. This paper aims at building a P2P CDN with high performance, scalability and robustness. Our proposed protocols combine DHT efficiency with gossip robustness and take into account the interests and localities of peers. In short, Flower-CDN provides a hybrid and locality-aware routing infrastructure for user queries. PetalUp-CDN is a highly scalable version of Flower-CDN that dynamically adapts to variable rates of participation and prevent overload situations. In addition, we ensure the robustness of our P2P CDN via low-cost maintenance protocols that can detect and recover from churn and dynamicity. Our extensive performance evaluation shows that our protocols yield high performance gains under both static and highly dynamic environments. Furthermore, they incur acceptable and tunable overhead. Finally we provide main guidelines to deploy Flower-CDN for the public use.     

Dynamic quorums for DHT-based enterprise infrastructures

Peer-to-peer systems (P2P) have become a popular technique to design large-scale distributed applications in unmanaged inter-domain settings, such as file sharing or chat systems, thanks to their capabilities to self-organize and evenly split the load among peers. Recently, enterprises owning a large IT hardware and software infrastructure started looking at these P2P technologies as a means both to reduce costs and to help their technical divisions to manage huge number of devices characterized by a high level of cooperation and a relatively low churn. Gaining a quick exclusive access to the system for maintenance or auditing purposes in these enterprise infrastructures is a fundamental operation to be implemented. Conversely, this kind of operation is usually not an issue in the previously mentioned inter-domain setting, where peers are inherently independent and cannot be managed.     

SmartPeerCast: a Smart QoS driven P2P live streaming framework

The P2P swarm technologies have been shown to be very efficient for medium scale content distribution systems in the last few years, such as the file sharing and video-on-demand (VOD) applications. However it is still an open topic about how to deploy the P2P paradigm for the real time video broadcasting (RTVB) applications. The P2P RTVB application is different from the cache based P2P system because it has more stringent restrictions for startup time and packet loss ratio. In this paper, an adaptive media broadcasting P2P framework named SmartPeerCast which employs the media transrating service to control the quality of service (QoS), is proposed. SmartPeerCast achieves a network awareness, codec awareness, and high performance RTVB service with four key designs: (1) It groups the newly joined peers into different quality clusters by their uploading capability. This clustering mechanism avoids the bandwidth bottleneck between the heterogeneous peers of the overall P2P overlay by only forwarding the same quality stream over the peers in the same cluster. (2) The streaming quality is adjusted adaptively between the sending and the receiving peers by a Smart QoS algorithm to compensate for the network jitters to reduce the receiving peer’s playback jitter. (3) The receiving peer monitors the data forwarding QoS of the sending peer to select the best suitable parent node dynamically. The SmartPeerCast uses this Smart QoS framework to implement an incentive mechanism to award the peers with high uploading contributions by migrating them to a higher quality cluster. (4) A transrating engine is used at the leaf nodes of the high quality cluster to forward the stream with suitable bits rate to the nodes of the low quality cluster; this transrating service not only can fully utilize the uploading bandwidth of the peers in the higher quality cluster but also avoids the bandwidth bottleneck of stream forwarding between the heterogeneous peers. Our experiment results and the real deployment show that SmartPeerCast can eliminate the bandwidth bottleneck and content bottleneck between the heterogeneous peers with a smaller startup time and packet loss and it is a high performance and medium scale P2P RTVB framework.     

Delay Management in Mesh-Based P2P Live Streaming Using a Three-Stage Peer Selection Strategy

Peer-to-peer (P2P) live streaming systems have gained popularity due to the self-scalability property of the P2P overlay networks. In P2P live streaming, peers retrieve stream content from other peers in the system. Therefore, peer selection strategy is a fundamental element to build an overlay which manages the playback delay and startup delay experienced by the peers. In this paper, we propose a peer selection strategy which manages to build a minimum delay overlay using three different stages of overlay construction. In the first stage, the tracker suggests some peers as prospective partners to a new peer. In the second stage, the peer selects its partners out of these peers such that delay is minimized. The third stage is the topology adaptation phase of peers, where peers reposition themselves in the overlay to maintain minimum delay during peer churn. In the proposed peer selection strategy, peers are selected in all the stages based on parameters such as propagation delay, upload capacity, buffering duration and buffering level. The proposed strategy is compared with two existing strategies in the literature: Fast-Mesh (Ren et al. in IEEE Trans Multimed 11: 1446, 2009) and Hybrid live p2p streaming protocol (Hammami et al., 2014) using simulations. Our results show that playback delay and startup delay are reduced significantly with the help of proposed strategy. We demonstrate that the stability of the system also improves during peer churn.