DCMP: A Distributed Cycle Minimization Protocol for Peer-to-Peer Networks

Broadcast-based peer-to-peer (P2P) networks, including flat (for example, Gnutella) and two-layer superpeer implementations (for example, Kazaa), are extremely popular nowadays due to their simplicity, ease of deployment, and versatility. The unstructured network topology, however, contains many cyclic paths, which introduce numerous duplicate messages in the system. Although such messages can be identified and ignored, they still consume a large proportion of the bandwidth and other resources, causing bottlenecks in the entire network. In this paper, we describe the distributed cycle minimization protocol (DCMP), a dynamic fully decentralized protocol that significantly reduces the duplicate messages by eliminating unnecessary cycles. As queries are transmitted through the peers, DCMP identifies the problematic paths and attempts to break the cycles while maintaining the connectivity of the network. In order to preserve the fault resilience and load balancing properties of unstructured P2P systems, DCMP avoids creating a hierarchical organization. Instead, it applies cycle elimination symmetrically around some powerful peers to keep the average path length small. The overall structure is constructed fast with very low overhead. With the information collected during this process, distributed maintenance is performed efficiently even if peers quit the system without notification. The experimental results from our simulator and the prototype implementation on PlanetLab confirm that DCMP significantly improves the scalability of unstructured P2P systems without sacrificing their desirable properties. Moreover, due to its simplicity, DCMP can be easily implemented in various existing P2P systems and is orthogonal to the search algorithms.     

消除R_TTL环:Gnutella网络中减少冗余消息的解决方法

基于Gnutella协议的peer-to-peer网络中，存在着大量的冗余消息，使得大规模Gnutella网络查询效率低下。经过研究发现，R-TTL环是网络中产生冗余消息的根本原因。本文提出了一种改进的Gnutella网络模型FR-Gnet，在FR-Gnet网络中没有R-TTL环，因而也没有冗余消息。本文最后给出了FRGnet模型的一种近似实现：在Gnutella协议中增加了两种消息——hello消息和bad消息，通过这两种消息来发现并断开网络中的R-TTL环。改进后的Gnutella网络中的冗余消息大大减少。     

Gnutella网络的连接管理

Gnutella是完全分布式、无结构的对等网络.它采用洪泛式的消息广播机制,使网络具有高鲁棒性和高动态性的同时,也使网络产生了呈指数级增长的冗余消息.在解析Gnutella网络消息广播机制的基础上,指出了Gnutella网络丢弃某些连接的必要性和可行性,提出了根据传输带宽和机器处理各种消息时所耗费的时间和资源,来划分Gnutella网络中消息的优先级.把评价搜索引擎性能的F-Measure参数引入连接管理中,在保障消息可达率的同时,通过计算丢弃某些冗余连接.该解决方案由丢弃连接管理算法(discarding connection management algorithm,简称DCMA)实现,还给出了算法实例和对算法的讨论.     

利用Gnutella网络的拓扑特性改进其可扩展性

分布式P2P网络Gnutella模型拓扑节点的分布不仅呈现典型的“幂规律”(PowerLaw),而且还具有明显的“小群体”(SmallWorld)特征。但是其对等机共享信息查询的搜索、定位路由协议仅使用“洪泛”算法,因此存在可扩展性问题。论文针对Gnutella网络拓扑节点具有的这些分布特性,提出了一种充分利用这些特性,基于“最大聚集度优先”的查询包路由改进策略,经模拟分析其协议的性能后证明,该策略能有效地提高Gnutella网络的可扩展性。     

基于子树间快捷连接的非结构化P2P资源搜索方法

通过对非结构化P2P网络资源搜索方法的研究,提出了一种P2P覆盖网络。网络采用多路平衡树形拓扑结构,当新节点加入时在其与根节点的各子树间创建仅参与查询消息第一跳转发的快捷连接,搜索过程中利用快捷连接实现查询消息在根的各子树间并行转发并且不依赖根节点。仿真比较了所提网络同Gnutella和随机漫步网络的性能,所提网络具有低消息冗余率、高搜索成功率和较低的平均搜索时间复杂度。分析结果表明所提网络在资源搜索方面是高效可行的。     

一种非结构化对等网络短路效应解决方法

非结构化对等网络Gnutella存在短路效应，这会严重影响消息的到达率，造成网络查询效率低下。利用Gnutella网络拓扑的分布呈现典型的幂规律和小世界特性，将少量度很大的节点提升为超级结点，并以超级节点为中心，将兴趣相同或相似的节点进行聚类，从而形成若干自治域小世界，这样Gnutella网络模型被抽象层次化，自治域内查询请求由本域的超级节点直接处理，自治域间查询请求在超级节点间进行转发。研究表明，这种方法可以有效解决短路效应问题。     

VANET中一种基于概率转发的AODV路由协议

泛洪被作为实现广播通信的最简单的技术,广泛应用于车联网VANET(vehicular Ad Hoc network)路由.然而,由于VANET中节点的快速移动以及网络拓扑动态变化,简单的泛洪容易导致大量的冗余数据包,并引发广播风暴.为此,以典型的按需式距离矢量路由协议AODV (Ad Hoc on-demand distance vector)为基础,提出基于概率转发的AODV路由协议,记为AODV_P.AODV_P协议利用概率转发机制替代AODV中的泛洪.节点利用距离、密度信息计算转发概率,并依据转发概率设置计时器.计时器时间越短,成为下一跳转发节点的可能性越大.仿真结果表明,提出的AODV_P能够有效降低冗余数据包,缓解广播风暴问题.与AODV协议相比,AODV_P在传输时延、数据包传输率方面得到了有效提高.     

Gnutella网络中的异构延迟现象及其解决方案

在基于Gnutella协议的Peer-to-Peer网络中,异构延迟是普遍存在的一种现象并严重影响网络中的信息传递。具体地分析了该现象对Gnutella网络性能的影响,重新定义了两种消息控制机制,提出了一种能有效消除该现象影响的解决方案。     

A Self-adaptive Algorithm for Topology Matching in Unstructured Peer-to-Peer Networks

Peer-to-peer networks are overlay networks that are constructed over underlay networks. These networks can be structured or unstructured. In these networks, peers choose their neighbors without considering underlay positions, and therefore, the resultant overlay network may have a large number of mismatched paths. In a mismatched path, a message may meet an underlay position several times, which causes redundant network traffic and end-to-end delay. In some of the topology matching algorithms called the heuristic algorithms, each peer uses a local search operator for gathering information about the neighbors of that peer located in its neighborhood radius. In these algorithms, each peer also uses a local operator for changing the connections among the peers. These matching algorithms suffer from two problems; neither the neighborhood radius nor the local operator can adapt themselves to the dynamicity of the network. In this paper, a topology matching algorithm that uses learning automata to adapt the neighborhood radius and an adaptation mechanism inspired from the Schelling segregation model to manage the execution of the local operator is proposed. To evaluate the proposed algorithm, computer simulations were conducted and then the results were compared with the results obtained for other existing algorithms. Simulation results have shown that the proposed algorithm outperforms the existing algorithms with respect to end-to-end delay and number of mismatched paths.     

非结构P2P网络受限搜索机制

降低搜索过程中产生的大量网络开销,是非结构P2P 网络重点研究内容之一.泛洪算法和随机查找算法简单且易于实现,但其在搜索过程中产生的大量冗余消息是造成大量网络开销的主要原因.针对这一问题,提出一种受限搜索机制(restricted forward search algorithm,简称RFSA),定义了搜索路径和冗余搜索路径,引入本地消息索引缓存机制,通过节点对消息的受限接收,消除节点对消息的重复接收与转发;利用搜索过程中携带的实时搜索路径信息,选择未出现在搜索路径中的邻居节点对消息进行转发,消除冗余搜索路径的产生.从理论上分析了RFSA 所产生的消息数目和网络开销.模拟实验分别从网络开销、查询点击率、搜索覆盖率和产生的冗余消息数目等方面对受限机制下和非受限机制下的泛洪算法和随机查找算法进行了对比分析,结果表明,在搜索覆盖率和查询点击率基本相同的情况下,受限机制下的泛洪算法和随机查找算法能够减少大量冗余消息的产生,降低了网络开销.     

Text-enhanced network representation learning

Network representation learning called NRL for short aims at embedding various networks into lowdimensional continuous distributed vector spaces. Most existing representation learning methods focus on learning representations purely based on the network topology, i.e., the linkage relationships between network nodes, but the nodes in lots of networks may contain rich text features, which are beneficial to network analysis tasks, such as node classification, link prediction and so on. In this paper, we propose a novel network representation learning model, which is named as Text-Enhanced Network Representation Learning called TENR for short, by introducing text features of the nodes to learn more discriminative network representations, which come from joint learning of both the network topology and text features, and include common influencing factors of both parties. In the experiments, we evaluate our proposed method and other baseline methods on the task of node classification. The experimental results demonstrate that our method outperforms other baseline methods on three real-world datasets.     

Resolving the Topology Mismatch Problem in Unstructured Peer-to-Peer Networks

Prior studies show that more than 70 percent of communication paths in a popular unstructured peer-to-peer (P2P) system (i.e., Gnutella) do not exploit the physical network topology, leading to the topology mismatch problem, and thus, lengthen communication between participating peers. While previous efforts in solving overlay topology matching problems do not guarantee the bounds of performance metrics (e.g., the communication delay between any two overlay peers and the broadcasting scope of any participating peer), in this paper, we present a novel topology matching algorithm that has provable performance qualities. In our proposal, each participating node creates and manages a constant number of overlay connections to other peers in a distributed manner. In rigorous performance analysis, we show that 1) the expected overlay communication delay between any two nodes in our P2P network is a constant; 2) in addition, any joining node has the exponential broadcasting scope in expectation; 3) furthermore, a participating node takes a polylogarithmic overhead to exploit the physical network locality and maintain its flooding scope. Together with extensive simulations, we present our proposal that significantly outperforms two recent solutions, i.e., THANCS and mOverlay, in terms of overlay communication latency and/or broadcasting scope.     

Gnutella环境下资源定位方法的改进

本文在已有研究的基础上提出了一种基于节点间部分通路的资源定位方法,加入节点基于邻居节点的逻辑度选择要建立链接的节点,请求节点通过所构建的逻辑结构来定位资源。仿真实验的结果表明,与传统广播方法相比,所提出的方法能有效地降低Gnutella网络的通讯负载,减少冗余消息,提高Gnutella网络的可扩展性,这些对于未来智能网络打印机的研发具有深远意义。     

Statistical models for Gnutella signaling traffic

The paper is focused on signaling traffic between Gnutella peers that implement the latest Gnutella protocol specifications (v0.6). In particular, we provide analytically tractable statistical models at session level, message level and IP datagram level for traffic crossing a Gnutella ultrapeer at Blekinge Institute of Technology (BTH) in Karlskrona, Sweden. To the best of our knowledge this is the first work that provides Gnutella v0.6 statistical models at this level of detail. These models can be implemented straightforward in network simulators such as ns2 and OmNet++.The results show that incoming requests to open a session follow a Poisson distribution. Incoming Gnutella messages across all established sessions can be described by a compound Poisson distribution. Mixture distribution models for message transfer rates include a heavy-tailed component.     

基于Gnutella协议的分布式Peer-to-Peer网络连接管理策略及改进研究

在分析Gnutella网络协议、消息传播和连接管理机制的基础上,提出了基于F-Measure算法的网络连接管理策略,在算法中引入了一个重要的指标F-Measure参数f:丢弃连接后消息的到达率,当网络过载时,选f值最大的连接断开;通过对Gnutella网络中的消息分类和设定优先级,建立缓冲时间机制保存丢弃连接上的重要信息,以最小的代价维护网络的鲁棒性;在应用层上采用Zig-Zag算法进行数据流控制,辅助F-Measure算法进行连接管理,有效地控制了Gnutella网络产生的请求Flood,使网络的连接管理具体数据化。最后,对F-Measure算法进行了性能分析和模拟。     

Cored-Based Tree with Forwarding Regions (CBT-FR); A Protocol for Reliable Multicasting in Mobile Ad Hoc Networks

In this paper we propose a new protocol for reliable multicast in a multihop mobile radio network. The protocol is reliable, i.e., it guarantees message delivery to all multicast nodes even when the topology of the network changes during multicasting. The proposed protocol uses a core-based shared tree. The multicast tree may get fragmented due to node movements. The notion of a forwarding region is introduced which is used to glue together fragments of multicast trees. The gluing process involves flooding the forwarding region of only those nodes that witness topology change due to node mobility. Delivery of multicast messages to mobile nodes is expedited through (i) pushing the message by witness nodes in their forwarding regions and (ii) pulling messages by a mobile node during (re)joining process. Hence, the protocol conserves network bandwidth by using a combination of the push–pull approach and by restricting flooding only to the essential parts of the network that are affected by topology change.  We develop a theoretical model to compute the probability of packet loss (as a function of the mobility rate) for our proposed scheme compared to the the core-based tree protocol (CBT); we also evaluate the effectiveness of forwarding regions as compared to traditional flooding. Our analysis shows that the proposed scheme significantly outperforms CBT.     

基于节点兴趣的非结构化P2P网络拓扑结构研究

针对非结构化P2P网络中资源搜索算法搜索效率低、冗余消息量过多等问题,结合非结构化P2P网络拓扑结构特点,提出一种基于节点兴趣的完全二叉树（CBT-BI）非结构化P2P覆盖网络拓扑结构。在兴趣相似度高的节点之间建立逻辑连接,根据兴趣相似度值在完全二叉树中按序排列;在资源搜索过程中,使用基于洪泛算法的双向资源搜索方法。仿真结果表明,该拓扑结构使得节点能在短时间内查找到有效的资源,减少查询消息量,缩短了平均路由路径,提高了资源搜索效率。     

Implications of the file names and user requested queries on Gnutella performance

The Gnutella file sharing system allows a large number of peers to share their local files. However, it does not coordinate the way by which these shared objects are named or how they are searched by other users; such decisions are made independently by each peer. In this work, we investigate the practical performance implications of this design. We collected the shared filenames and user generated queries over a three-year period. We show the mismatch between these naming mechanisms. We show the fundamental limitations of Gnutella performance that cannot be addressed by improvements in overlays or by varying the search mechanisms alone. Based on our observations, we describe two practical approaches to improve Gnutella performance. We describe a mechanism to build the file term synopsis using the observed popularity of queries routed through the ultrapeer. We also describe a query transformation mechanism that improves the success rates for failed queries.     

GAER: genetic algorithm-based energy-efficient routing protocol for infrastructure-less opportunistic networks

In infrastructure-less opportunistic networks (Oppnets), the routing of messages is a challenging task since nodes are not aware of the network topology and they look for an opportunity to send the message by finding or predicting a best temporary path at each hop towards the destination. As nodes perform various computations for next hop selection, a lot of battery power gets consumed, which in turn reduces the network lifetime. Thus, there is a clear demand for routing protocols for such networks which are energy-efficient and consume lesser power of nodes in forwarding a message. In this paper, a novel routing protocol named genetic algorithm-based energy-efficient routing (GAER) protocol for infrastructure-less Oppnets is proposed. This protocol uses a node’s personal information, and then applies the genetic algorithm (GA) to select a better next hop among a group of neighbour nodes for the message to be routed to the destination. With the application of GA, optimal results are obtained that help in the selection of the best possible node as the next hop, which in turn, leads to prolonged battery life. Simulation results show that GAER outperforms the Epidemic, PROPHET, and Spray and Wait protocols in terms of messages delivered, overhead ratio, average residual energy, and number of dead nodes. The results obtained for average latency and average buffer time using GAER are comparable to those obtained for the aforementioned protocols.