Modeling structured peer-to-peer systems

1 Introduction File sharing software napster and gnutella arouse an increa- sing interest in the peer-to-peer(P2P)network where all the nodes have identical capabilities and responsibilities and directly communicate with each other without centralized con…     

Addressing, distances and routing in triangular systems with applications in cellular networks

Triangular systems are the subgraphs of the regular triangular grid which are formed by a simple circuit of the grid and the region bounded by this circuit. They are used to model cellular networks where nodes are base stations. In this paper, we propose an addressing scheme for triangular systems by employing their isometric embeddings into the Cartesian product of three trees. This embedding provides a simple representation of any triangular system with only three small integers per vertex, and allows to employ the compact labeling schemes for trees for distance queries and routing. We show that each such system with n vertices admits a labeling that assigns O(log ² n) bit labels to vertices of the system such that the distance between any two vertices u and v can be determined in constant time by merely inspecting the labels of u and v, without using any other information about the system. Furthermore, there is a labeling, assigning labels of size O(log n) bits to vertices, which allows, given the label of a source vertex and the label of a destination, to compute in constant time the port number of the edge from the source that heads in the direction of the destination. These results are used in solving some problems in cellular networks. Our addressing and distance labeling schemes allow efficient implementation of distance and movement based tracking protocols in cellular networks, by providing information, generally not available to the user, and means for accurate cell distance determination. Our routing and distance labeling schemes provide elegant and efficient routing and connection rerouting protocols for cellular networks. Victor Chepoi received the M.S. degree in Applied Mathematics and Computer Science from Moldova State University, in 1983, and the PhD degree in Theoretical Computer Science from the Belorussian Academy of Sciences, in 1987. He was an Assistant and then an Associate Professor at the Mathematics and Computer Science Department of Moldova State University from 1987 to 1994. He was awarded the Alexander von Humboldt Shtiftung Fellowship from 1994 to 1995 at the University of Hamburg, Germany. During 1995 to 1997, he was a Visiting Professor at the Laboratoire de Biomathematiques, Universite de la Mediterranee, France. During 1998, he was a Fellow at SFB343 “Diskrete Strukturen in der Mathematik”, University of Bielefeld, Germany. Since September 1998 he has been a Professor of Computer Science at Faculte des Sciences de Luminy, Universite de la Maditerranee, France. His research interests include graph theory and combinatorics, design and analysis of network and graph algorithms, geometry and algorithmics of metric spaces, computational geometry, and approximation algorithms. Feodor F. Dragan received the M.S. degree in Applied Mathematics and Computer Science from Moldova State University, in 1985, and the PhD degree in Theoretical Computer Science from the Belorussian Academy of Sciences, in 1990. He was an Assistant and then an Associate Professor at the Mathematics and Computer Science Department of Moldova State University from 1988 to 1999. From 1994 to 1999, he was on leave of absence and worked in Germany as a Research Associate on a Volkswagen Foundation (VW) project and on a German Research Community (DFG) project. He was also awarded a DAAD Research Fellowship (Germany) from 1994 to 1995. During 1999 to 2000, he was a Research Associate at the Computer Science Department of University of California, Los Angeles. Since August 2000 he has been with Kent State University and he is currently an Associate Professor of Computer Science. He has authored more than 70 refereed scientific publications. His research interests include design and analysis of network algorithms, algorithmic graph and hypergraph theory, computational geometry, VLSI CAD, and combinatorial optimization. Yann Vaxes received the PhD degree in Computer Science from the Universite de la Mediterranee, in 1998. Then, he joined the Computer Science Department of this university as an Assistant Professor. His research interests include design and analysis of network algorithms, algorithmic graph theory and combinatorial optimization.     

BALLS: A structured peer-to-peer system with integrated load balancing

Load balancing is an important problem for structured peer-to-peer systems. We are particularly interested in the consumption of network bandwidth for routing traffic and in the usage of computer resources for object storage. In this paper, we investigate the possibility to simultaneously balance these two types of load. We present a structured peer-to-peer overlay that efficiently performs such simultaneous load balancing. The overlay is constructed by partitioning the nodes of a de Bruijn graph and by allocating the partitions to the peers. Peers balance network bandwidth consumption by repartitioning the nodes. Balancing of computer resources for storage is enabled by dissociating the actual storage location of an object from the location of its search key. The paper presents and analyzes the protocols required to maintain the overlay structure and perform load balancing. We demonstrate their efficiency by simulation. We also compare our proposed overlay network with other approaches.     

Performance analysis and fault tolerance of randomized routing on Clos networks

Beside universality and very low latency, Youssef's randomized self-routing algorithms [25] have high tolerance for multiple faults and more strikingly have the potential for fault tolerance without diagnosis. In this paper we study the performance of Youssef's routing algorithms for faulty Clos networks in the presence of multiple faults in multiple columns with and without fault detection. We show that with fault detection and diagnosis, randomized routing algorithms provide scalable, very efficient and fault tolerant routing mechanisms. Without fault detection and diagnosis, randomized routing provides good fault tolerance for faulty switches in either the first or the second column. The delays become large for faults in the third column or for faults in more than one column. In conclusion, randomized routing enables the system to run without periodic fault detection/diagnosis, and if and when the performance degrades beyond a certain threshold, diagnosis can be performed to improve the routing performance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Free-riding and whitewashing in peer-to-peer systems

We devise a model to study the phenomenon of free-riding and free-identities in peer-to-peer systems. At the heart of our model is a user of a certain type, an intrinsic and private parameter that reflects the user's willingness to contribute resources to the system. A user decides whether to contribute or free-ride based on how the current contribution cost in the system compares to her type. We study the impact of mechanisms that exclude low type users or, more realistically, penalize free-riders with degraded service. We also consider dynamic scenarios with arrivals and departures of users, and with whitewashers -users who leave the system and rejoin with new identities to avoid reputational penalties. We find that imposing penalty on all users that join the system is effective under many scenarios. In particular, system performance degrades significantly only when the turnover rate among users is high. Finally, we show that the optimal exclusion or penalty level differs significantly from the level that optimizes the performance of contributors only for a limited range of societal generosity levels.     

Performance analysis of minimal path fault tolerant routing in NoC

Occurrence of faults in Network on Chip (NoC) is inevitable as the feature size is continuously decreasing and processing elements are increasing in numbers. Faults can be revocable if it is transient. Transient fault may occur inside router, or in the core or in communication wires. Examples of transient faults are overflow of buffers in router, clock skew, cross talk, etc.. Revocation of transient faults can be done by retransmission of faulty packets using oblivious or adaptive routing algorithms. Irrevocable faults causes non-functionality of segment and mainly occurs during fabrication process. NoC reliability increases with the efficient routing algorithms, which can handle the maximum faults without deadlock in network. As transient faults are temporary and can be easily revoked using retransmission of packet, permanent faults require efficient routing to route the packet by bypassing the nonfunctional segments. Thus, our focus is on the analysis of adaptive minimal path fault tolerant routing to handle the permanent faults. Comparative analysis between partial adaptive fault tolerance routing West-First, North-Last, Negative-First, Odd Even, and Minimal path Fault Tolerant routing (MinFT) algorithms with the nodes and links failure is performed using NoC Interconnect RoutinG and Application Modeling simulator (NIRGAM) for the 2D Mesh topology. Result suggests that MinFT ensures data transmission under worst conditions as compared to other adaptive routing algorithms.     

A performance study of BitTorrent-like peer-to-peer systems

This paper presents a performance study of BitTorrent-like P2P systems by modeling, based on extensive measurements and trace analysis. Existing studies on BitTorrent systems are single-torrent based and usually assume the process of request arrivals to a torrent is Poisson-like. However, in reality, most BitTorrent peers participate in multiple torrents and file popularity changes over time. Our study of representative BitTorrent traffic provides insights into the evolution of single-torrent systems and several new findings regarding the limitations of BitTorrent systems: (1) Due to the exponentially decreasing peer arrival rate in a torrent, the service availability of the corresponding file becomes poor quickly, and eventually it is hard to locate and download this file. (2) Client performance in the BitTorrent-like system is unstable, and fluctuates significantly with the changes of the number of online peers. (3) Existing systems could provide unfair services to peers, where a peer with a higher downloading speed tends to download more and upload less. Motivated by the analysis and modeling results, we have further proposed a graph based model to study interactions among multiple torrents. Our model quantitatively demonstrates that inter-torrent collaboration is much more effective than stimulating seeds to serve longer for addressing the service unavailability in BitTorrent systems. An architecture for inter-torrent collaboration under an exchange based instant incentive mechanism is also discussed and evaluated by simulations     

Structured peer-to-peer systems for telecommunications and mobile environments

The peer-to-peer (P2P) paradigm not only allows end users to share own resources, but is also regarded as a new networking paradigm due to its robust, self-organizing character, abandoning infrastructure and relying on end-users equipment. In contrast to common fixed-line Internet file sharing P2P systems, in this paper, we address critical issues regarding scalable personal communications and heterogeneous mobile systems. We discuss challenges and present our solutions based on structured P2P.     

On the fundamental tradeoffs between routing table size and network diameter in peer-to-peer networks

We study a fundamental tradeoff issue in designing a distributed hash table (DHT) in peer-to-peer (P2P) networks: the size of the routing table versus the network diameter. Observing that existing DHT schemes have either 1) a routing table size and network diameter both of O(log/sub 2/n), or 2) a routing table of size d and network diameter of O(n/sup 1/d/), S. Ratnasamy et al. (2001) asked whether this represents the best asymptotic "state-efficiency" tradeoffs. We show that some straightforward routing algorithms achieve better asymptotic tradeoffs. However, such algorithms all cause severe congestion on certain network nodes, which is undesirable in a P2P network. We rigorously define the notion of "congestion" and conjecture that the above tradeoffs are asymptotically optimal for a congestion-free network. The answer to this conjecture is negative in the strict sense. However, it becomes positive if the routing algorithm is required to eliminate congestion in a "natural" way by being uniform. We also prove that the tradeoffs are asymptotically optimal for uniform algorithms. Furthermore, for uniform algorithms, we find that the routing table size of O(log/sub 2/n) is a magic threshold point that separates two different "state-efficiency" regions. Our third result is to study the exact (instead of asymptotic) optimal tradeoffs for uniform algorithms. We propose a new routing algorithm that reduces the routing table size and the network diameter of Chord both by 21.4% without introducing any other protocol overhead, based on a novel number-theory technique. Our final result is to present Ulysses, a congestion-free nonuniform algorithm that achieves a better asymptotic "state-efficiency" tradeoff than existing schemes in the probabilistic sense, even under dynamic node joins/leaves.     

Bayes analysis for fault location in distributed systems

The authors propose a simple and practical probabilistic model, using multiple incomplete test concepts, for fault location in distributed systems using a Bayes analysis procedure. Since it is easier to compare test results among processing units, their model is comparison-based. This approach is realistic and complete in the sense that it does not assume conditions such as permanently faulty units, complete tests, and perfect or nonmalicious environments. It can handle, without any overhead, fault-free systems so that the test procedure can be used to monitor a functioning system. Given a system S with a specific test graph, the corresponding conditional distribution between the comparison test results (syndrome) and the fault patterns of S can be generated. To avoid the complex global Bayes estimation process, the authors develop a simple bitwise Bayes algorithm for fault location of S, which locates system failures with linear complexity, making it suitable for hard real-time systems. Hence, their approach is appealing both from the practical and theoretical points of view     

Study of the relationship between peer-to-peer systems and IP multicasting

Peer-to-peer (P2P) systems, which have attracted public attention, involve a number of directly connected "peers" exchanging various types of information among themselves. However, applications based on P2P systems generally generate a lot of traffic and require not only the resources of every peer (e.g., CPU, memory, and bandwidth) but also many network resources. We think the main problems of P2P systems can be solved using IP multicasting, which is becoming popular as an effective way to transfer streaming media over the network and can reduce network traffic and the load on a streaming server. We propose applying IP multicasting to P2P systems. After mentioning that almost every application can be improved by our proposal, we discuss which routing protocol is suitable. Finally, we show that we can get good results even when part of the network does not support IP multicasting.     

广电系统SDH传输网络故障的分析与处理

对广播电视SDH传输网络的结构特点进行分析,着重介绍了影响SDH传输网络安全的常见故障、告警分析、故障定位及SDH自愈保护环的启动机制。通过SDH设备实际维护过程中遇到的典型故障案例,从网络系统的角度去分析告警现象,探讨处理方法,为SDH传输网络的故障分析处理提供参考。     

ESSPR: an efficient secure routing scheme based on searchable encryption with vehicle proxy re-encryption for vehicular peer-to-peer social network

In this paper, we propose an Efficient Secure routing Scheme based on searchable encryption with vehicle Proxy Re-encryption, called ESSPR, for achieving privacy preservation of message in vehicular peer-to-peer social network (VP2PSN). Specifically, the proposed ESSPR scheme consists of six phases: system initializations phase, peer registration phase, document generation phase, document forwarding phase, vehicle proxy re-encryption phase, and document receiving phase. Based on rationale of QoS-based clustering strategy, public key encryption with keyword search, identity based aggregate signature, and proxy re-encryption, ESSPR provides privacy for keyword, privacy for resources, and authentication and data integrity of the demand’s source. In addition, ESSPR is robust against eavesdropping attack, wormhole attack, packet analysis attack, packet tracing attack, and replay attack. Through performance evaluation, we demonstrate the effectiveness of ESSPR in terms of delivery ratio, average delay, average fairness, and detection ratio under malicious peers proportions in VP2PSN.     

Design and analysis of parallel file downloading algorithms in peer-to-peer networks

It is well known that the method of parallel downloading can be used to reduce file download times in a peer-to-peer (P2P) network. There has been little investigation on parallel download and chunk allocation for source peers with random service capacities. The main contribution of this paper is to address the problem of efficient parallel file download in P2P networks with random service capacities. A precise analysis of the expected download time is given when the service capacity of a source peer is a random variable. A general framework is developed for analyzing the expected download time of a parallel download and chunk allocation algorithm, and is applied to the analysis of several algorithms. Two chunk allocation algorithms for parallel download are proposed. It is observed that the performance of parallel download can be significantly improved by using the method of probing high-capacity peers. One such algorithm is proposed and its expected parallel download time is analyzed. The performance of these parallel file download algorithms in P2P networks with random service capacities are compared. The above parallel download algorithms are extended to multiple file download by dividing source peers into clusters. It is noticed that there is an important issue of optimal parallelism which minimizes the combined effect of intracluster and intercluster overhead of parallel download and load imbalance.     

Dependability analysis of systems with on-demand and active failuremodes, using dynamic fault trees

Safety systems and protection systems can experience two phases of operation (standby and active); an accurate dependability analysis must combine an analysis of both phases. The standby mode can last for a long time, during which the safety system is periodically tested and maintained. Once a demand occurs, the safety system must operate successfully for the length of demand. The failure characteristics of the system are different in the two phases, and the system can fail in two ways: (1) it can fail to start (fail on-demand), or (2) it can fail while in active mode. Failure on demand requires an availability analysis of components (typically electromechanical components) which are required to start or support the safety system. These support components are usually maintained periodically while not in active use. Active failure refers to the failure while running (once started) of the active components of the safety system. These active components can be fault tolerant and use spares or other forms of redundancy, but are not maintainable while in use. The approach, in this paper, automatically combines the "availability analysis of the system in standby mode" with the "reliability analysis of the system in its active mode." The general approach uses an availability analysis of the standby phase to determine the initial state probabilities for a Markov model of the demand phase. A detailed method is presented in terms of a dynamic fault-tree model. A new "dynamic fault-tree construct" captures the dependency of the demand-components on the support systems, which are required to detect the demand or to start the demand system. The method is discussed using a single example sprinkler system and then applied to a more complete system taken from the off-shore industry     

Graph-theoretic proof of a network theorem and some consequences

A graph-theoretic proof of a network theorem is given. Some consequences of this theorem in relation to the analysis of an algorithm are discussed.     

针对有限TCAM的SDN网络灵活局部路由故障恢复

在软件定义网络中,使用大量的备份路径的转发规则会频繁地在交换机上进行数据流驱动,会增加带宽需求和处理延迟。对此,开发一组问题优化模型,可最小化备份路径所需的额外规则和带宽数量。由于该问题的计算复杂性,设计两个启发式算法计算备份路径:前向局部路由(FLR)和后向局部路由(BLR),从而提高TCAM和带宽的使用效率,并基于网络状态采用FLR和BLR设计了灵活自适应故障恢复框架。最后,通过在Internet 2网络拓扑上的仿真实验,显示所提算法在故障数据的抑制上要优于选取的对比算法,验证了算法性能优势。     

A novel and efficient routing architecture for multi-FPGA systems

Multi-FPGA systems (MFSs) are used as custom computing machines, logic emulators and rapid prototyping vehicles. A key aspect of these systems is their programmable routing architecture which is the manner in which wires, FPGAs and field-programmable interconnect devices (FPIDs) are connected. Several routing architectures for MFSs have been proposed, and previous research has shown that the partial crossbar is one of the best existing architectures. In this paper, we propose a new routing architecture, called the hybrid complete-graph and partial-crossbar (HCGP) which has superior speed and cost compared to a partial crossbar. The new architecture uses both hard-wired and programmable connections between the FPGAs. We compare the performance and cost of the HCGP and partial crossbar architectures experimentally, by mapping a set of 15 large benchmark circuits into each architecture. A customized set of partitioning and interchip routing tools were developed, with particular attention paid to architecture-appropriate interchip routing algorithms. We show that the cost of the partial crossbar (as measured by the number of pins on all FPGAs and FPIDs required to fit a design), is on average 20% more than the new HCGP architecture and as much as 25% more. Furthermore, the critical path delay for designs implemented on the partial crossbar were on average 20% more than the HCGP architecture and up to 43% more. Using our experimental approach, we also explore a key architecture parameter associated with the HCGP architecture-the proportion of hard-wired connections versus programmable connections-to determine its best value     

Analysis of fault tolerant computer systems

In many critical applications of digital systems, fault tolerance has been an essential architectural attribute for achieving high reliability. In recent years, the concept of the performability of such systems has drawn the attention of many researchers. In this paper we develop a general Markov model for fault tolerant computer systems. Various important performance measures, including the performability measures as well as some new performance measures, are treated in a unified manner. Furthermore, general and efficient computational procedures are developed for calculating these performance measures based on the uniformization technique of Keilson. A numerical example is given to illustrate the computational procedures developed.