基于资源路由表的P2P资源查找机制研究

对等网络使用户共享和访问网络中的大量资源，但随着网络规模的扩大，原有的资源查找机制已不能满足P2P环境下查找效率与网络负载的要求。文中结合P2P相邻节点的路径选择与Internet中的路由器选路具有的相似性．给出了一种新的资源查找方法——资源路由表查找法，并以此为基础构造了一个二层P2P资源查找模型，对其中的关键问题和方法给予了详细描述．并分析了该模型的性能。     

P2P网络中一种新的多层多维信誉模型

现有的信任模型大多通过单一信任值来判定节点的好坏,这种方法无法抵抗网络中的某些恶意行为,特别是对于P2P网络中独有的搭便车行为、＂公共物品的悲哀＂等问题,缺乏有效的抑制。针对这些问题,文中针对P2P网络提出了一种新的多层多维信誉模型,通过节点的信任值、贡献值、资源值等不同维度综合评价节点的信誉,并且按照信誉将节点划分为不同层次。分析可知该模型可以有效抵御多种恶意行为及多种自私行为,并能解决传统信任模型产生的一些性能问题。     

P-Chord:一种基于分区的Chord路由模型

在P2P系统中,有效地定位分布在网络中不同节点的数据资源一直是研究的重点。结构化P2P网络Chord的路由表存在着严重的信息冗余,影响了整个系统的效率。针对这种情况,文中在Chord的基础上提出了一种基于分区的Chord路由模型(P-Chord),通过对Chord的分区,将节点的路由表进行改造,消除了冗余信息,增加了有效信息。试验结果表明,P-Chord在保持Chord其他性能的前提下,减少了平均查找跳数,提高了查找效率。     

P2P网络层次化信任模型

大规模文件共享P2P网络中节点之间发生重复交易的可能性较小而难以建立信任关系,从而导致P2P网络容易受到恶意节点攻击。针对该问题本文提出了基于群组的P2P网络层次化信任模型。该信任模型将信任关系划分为群组之间的信任关系,群组与节点之间的信任关系和节点之间的信任关系3个层次。节点利用本地信任信息或所属群组的推荐信任确定给定节点的信任值。仿真分析表明,该信任模型能够有效识别恶意节点,使P2P网络中合作节点具有较高的成功请求率。     

基于P2P的简单查找算法设计

随着P2P系统的发展.它在Internet上的应用越来越广泛,尤其是对分布式数据对象的查找.为此,提出一种基于对等网络系统的简单查找方法.在假设具有N个固定节点的良好状态P2P网络环境中,利用一致哈希函数把给定的关键字随机方法映射到一个虚拟标识环的节点上,在标识环中每个节点根据自身路由表的信息查找指定关键字的映射.由方法讨论和性能分析可知,该方法是一种正确高效的查找分布式数据方法,用它可缩小存储空间的占用.     

移动自组网上结构化P2P网络Churn问题分析

分析研究了在三种用户行为的指数分布模型、Pareto分布模型和Weibull分布模型下,Churn问题对移动自组网上结构化P2P网络性能的影响.仿真实验研究表明,影响结构化P2P网络在移动自组网上工作性能的主要因素是节点会话时长、网络规模和节点密度、网络层路由协议以及节点移动性,并分析了这些主要因素之间的相互关系.     

基于P2P网络的Web Services发现机制

提出一种改进的两层混合式P2P网络模型,用该模型作为web Services发现技术的底层网络.该网络模型主要在两方面进行改进:在网络结构方面提出CP节点分类策略和SP节点分组策略;在网络组织方面提出一种基于Web Services兴趣因子空间的节点分布自调整策略.     

一种分层的P2P网络模型

基于分布式哈希表(DHT)的结构化P2P网络是目前研究热点,但是DHT机制实现比较复杂,更重要的是节点频繁的加入或退出所造成的网络动荡会对系统的网络造成巨大的压力,网络系统的稳定性很差。文章提出了一种层次化的P2P网络模型,该网络模型分为两层,其中上层是结构化Chord网络,下层中心化网络,该网络结合了结构化和中心化P2P网络的优点,弱化或克服了两者的缺点,在稳定性、可扩展性和查询效率等方面的性能都有一定的提高。     

对等网络资源搜索模型研究

为了提高结构化P2P网络的查询性能,提出P2P网络搜索延时模型,通过分析结构化P2P网络的搜索过程,利用马尔可夫链,得出P2P网络平均节点会话时间和搜索延时之间的关系。该模型展现了P2P Churn与网络性能之间的内在规律,进而达到改善结构化P2P的性能和应用范围的目的。     

Cloud-P2P云存储结构的模型建立与性能分析

基于Cloud-P2P云存储结构,针对云中心和P2P节点存储层数据副本的访问机制,考虑节点存储层数据副本的修复过程,建立一个三维连续时间Markov链模型。使用矩阵几何解方法导出该模型的稳态解,并给出节点存储层传输率,数据访问延迟和副本修复率等系统性能指标的表达式。通过数值实验和系统仿真定量刻画数据副本数等系统参数对Cloud-P2P云存储结构性能的影响。构造利润函数,进行用户存储层副本数的优化设置。     

Optimal layer division for low latency in DHT‐based hierarchical P2P network

Hierarchical architecture can significantly reduce the workload overheads and facilitate effective search in peer‐to‐peer (P2P) network by dividing the peers into two layers: a supernode layer and an ordinary node layer. System scalability is therefore improved, which is critical to the deployment of P2P applications, particularly for the P2P‐based Voice over Internet Protocol systems. However, the lack of appropriate size ratio of the supernode layer to the ordinary node layer makes the system search performance far from being optimal. To address the problem, the goal of this paper is to find the optimal layer ratio, such that lookup latency is minimized, subject to the capacity constraint of supernodes. With this particular objective, this paper first formulates a search delay model for the distributed hash table (DHT)‐based layered P2P architecture, taking account of two main sources of latency: DHT routing and queuing delay at the supernode. Then the optimal ratio between supernodes and ordinary nodes is found with the analytical model. Simulation and numerical results show that the obtained solution can improve the performance of a two‐layer P2P system in terms of lookup latency. Copyright © 2016 John Wiley & Sons, Ltd.     

商业生态系统的扩展性研究

提出一个两层的商业生态系统模型,上层网络中的用户进行商业活动,构成一个生态系统;下层网络由多个查询服务器组成,构成分布式查询系统,供上层用户注册其服务代理以及查找服务.上层和下层网络随时间不断演化且相互影响.在该模型的基础上,研究下层分布式系统的可扩展性.实验表明,该系统是可扩展的,并通过比较得出影响可扩展性的因素.     

基于双层P2P架构的VoD系统

本文提出的视频点播系统基于双层P2P架构实现,由城域网与驻地网媒体内容分发构成2级数据分发服务平台,用户终端点播并接受视频服务的同时,还能为其他用户提供数据服务,双层P2P架构有效地扩展了系统带宽,增强了服务能力,降低了系统成本,并提供QoS保证.     

An algorithm for the selection of effective error correction coding in wireless networks based on a lookup table structure

In this paper, we propose an adaptive Forward Error Correction (FEC) coding algorithm at the Medium Access Control (MAC) layer used in wireless networks. Our algorithm is based on the lookup table architecture, including a distance lookup table and a bit error rate lookup table. These tables will store the best value of the FEC codes based on different distances and bit error rates. Because radio channels change over time, the bit error rate is always changing, or in the case of mobile nodes, when the transmission distance changes, the bit error rate also changes, so previously proposed algorithms take longer to find the optimal value of the FEC code for data transmission. Our proposed algorithm, however, is based on 2 lookup tables, and thus, it can always quickly select an optimal FEC code during early data transmissions and achieve high performance. We compare our algorithm with other methods based on performance metrics such as the recovery overhead of FEC codes, energy efficiency, and peak‐signal‐to‐noise ratio values in the case of image transmission. Our simulation indicates that the proposed algorithm achieves better performances and proves the correctness of the proposed lookup table architecture.     

Query routing mismatch alleviation architecture for P2P file lookup in MANETs

A cross-layer optimized query routing mismatch alleviation(QRMA)architecture is proposed to mitigate the problem of query routing mismatch(QRM)phenomenon between the structured peer to peer(P2P)overlay and the routing layer in mobile Ad-hoc networks(MANETs),which is an important issue that results in the inefficiency of lookup process in the system.Explicated with the representative Chord protocol,the proposal exploits the information of topologic neighbors in the routing layer of MANETs to find if there is any optimized alternative next hop in P2P overlay during conventional lookup progress.Once an alternative next hop is detected,it will take the shortcut to accelerate the query procedure and therefore alleviate the QRM problem in scalable MANETs without any assistance of affiliation equipments such as GPS device.The probability of finding out such an alternative node is formulated and the factors that could increase the chance are discussed.The simulation results show that the proposed architecture can effectively alleviate the QRM problem and significantly improve the system performance compared with the conventional mechanism.     

一种可扩展的常数度P2P系统

DBR图是一种节点出度和入度均为2的常数度的图.通过将DBR图应用到动态网络,设计并实现了一种可扩展的常数度的P2P系统.对于节点规模为N的Tangram系统,路由表大小为O(1),平均路由步数是O(logN).通过模拟网络的实验表明,Tangram系统具有高效的查询性能,平均路由步数显著低于其他常数度P2P系统,在不同的节点在线率情况下性能稳定.     

Combining Task Scheduling in Power Adaptive Dynamic Reconfigurable System

Supplying the electronic equipment by exploiting ambient energy sources is a hot spot. In order to achieve the match between power supply and demands under the variance of environments at real time, a reconfigurable technique is taken. In this paper, a dynamic power consumption model by using a lookup table as a unit is proposed. Then, we establish a system-level task scheduling model according to the task type. Based on single instruction multiple data (SIMD) architecture which contains a processing system and a control system with a Nios Ⅱ processor, a practical dynamic reconfigurable system is built. The approach is evaluated on a hardware platform. The test results show that the system can automatically adjust the power consumption in case of external energy input changing. The utilization of the system dynamic power of their portion is from 80.05% to 91.75% during the first task assignment. During the entire processing cycle, the total energy efficiency is 97.67%.     

A low-power direct digital frequency synthesiser

This work presents a low power direct digital frequency synthesiser (DDFS) by using a new two-level lookup table algorithm. The algorithm uses trigonometric double angle formula to divide lookup table ROM into two parts. The ROM size of the proposed architecture is 25% less than that of conventional lookup table DDFS. The hardware of new DDFS architecture compared to the traditional two-level table DDFS also requires less one multiplication. A synthesised 0.35 µm DDFS with an spurious free dynamic range of ?80 dB, runs up to 100 MHz and consumes 81 mW at 3.3 v. The power efficiency is 0.81 mW MHz^?1, which represents an enhancement of more than 38% compared to the conventional DDFS.     

基于三层P2P结构的网格资源发现模型

在现有P2P技术的基础上,设计并实现了一种三层P2P网络.在原有SuperNode P2P结构的基础上进行了改进并增加一层功能节点.该结构中功能节点被用来存储从各个SuperNode收集的特定种类的网格资源信息.通过增加功能节点层可以很好地提高目前基于P2P技术的资源发现的效率,并且有效减少单点失效的问题.     

Low-Power System Design for MPEG-2/4 AAC Audio Decoder Using Pure ASIC Approach

This paper presents an implementation of a low-power and pure-hardware advanced-audio-coding (AAC) audio decoder system. Based on the characteristics of each decoding block, the AAC system is partitioned into four separate modules. For low-power and low-complexity considerations, architectural- and algorithmic-level approaches are adopted in both individual modules and whole system. In parallel PLA-based codeword decoder, we achieve a constant output rate of Huffman decoding in 2.5 cycles for the worst case, and memory usage is decreased compared to that in the binary-tree memory-based method. In reduced lookup table inverse quantizer, a table lookup with interpolation scheme is adopted which reduces the size of the lookup table from 8192 to 256. In hardware-shared signal processor, we use a hardware-sharing technique which integrates several similar blocks into a common hardware to reduce cost and enhance hardware utilization. In fully pipelined filterbank, a fast algorithm decreases the numbers of multiplication and addition largely to factors of 24 and 144 for the short and long blocks, respectively. A corresponding hardware for filterbank processing is proposed with fully pipelined architecture. Referring to stereo processing, a single hardware is shared for the channel pairs with low-cost consideration. The hardware operations of each module are well scheduled with high utilization of pipeline, and furthermore, the parallel processing among blocks is joined to increase efficiency. A 48% power savings can be reached by using the pipeline and parallel techniques of the channel pair. The proposed AAC decoder is realized in UMC 0.18-${rm mu}hbox{m}$ 1P6M technology and is operated at only 3 MHz in the worst case. The power dissipation is only 2.45 mW at the sampling frequency of 44.1 kHz.