OpenBSD下基于CARP协议的负载均衡防火墙研究

0PenBSD的安全性使其赢得了大量忠实的用户,尤其存网络路由、防火墙上的表蜕,被学校大量作为防火墙（NAT）使用。本系统丛于OpenBSD,利用CARP协议实现了防火墙之间的负载均衡,提高了防火墙的可用性;存实验测试中运行良好、性能稳定。     

A congestion-aware search protocol for heterogeneous peer-to-peer networks

Peer-to-Peer (P2P) file sharing is the hottest, fastest growing application on the Internet. When designing Gnutella-like applications, the most important consideration is the scalability problem, because P2P systems typically support millions of users online concurrently. Gnutella suffers from poor scaling due to its flooding-based search, resulting in excessive amounts of repeated query messages. Therefore, a good search protocol plays an important role in a system’s scalability. However, congestion, due to large query loads from users, definitely impacts on the performance of search protocols, and this consideration has received little attention from the research community. In this paper, we propose a congestion-aware search protocol for unstructured P2P networks. Our protocol consists of three parts—Congestion-Aware Forwarding, Random Early Stop and Emergency Signaling. The aim of our protocol is to integrate congestion control and object discovery functionality so that the search protocol can achieve good performance under congested networks and flash crowds. We perform extensive simulations to study our proposed protocol. The results show that our protocol can significantly reduce the hit delay while maintaining the high hit rate and also the congestion problems such as query loss and the peer overloading problem can be effectively alleviated.     

WSN自适应负载均衡集簇分层路由协议

结合考虑传统无线传感器网络(wireless sensor networks,WSN)路由协议特点以及实际应用中节点的不对等性,提出了一种自适应负载均衡集簇分层路由协议——ALBCH.该协议在簇头选举时引入剩余能量等相关因子,将贪婪算法成链机制分别引入分层路由协议的簇内通信和簇头间通信,对贪婪算法成链机制进行了一些改进.仿真结果表明,ALBCH能更有效地均衡网络负载,具有更好的健壮性和更高的实时性能,同时解决了传统协议在处理异构网络时的局限性.     

Semantic indexing in structured peer-to-peer networks

The past few years have seen tremendous advances in distributed storage infrastructure. Unstructured and structured overlay networks have been successfully used in a variety of applications, ranging from file-sharing to scientific data repositories. While unstructured networks benefit from low maintenance overhead, the associated search costs are high. On the other hand, structured networks have higher maintenance overheads, but facilitate bounded time search of installed keywords. When dealing with typical data sets, though, it is infeasible to install every possible search term as a keyword into the structured overlay.     

A novel group consensus protocol for heterogeneous multi-agent systems

In this paper, we consider the group consensus problem of heterogeneous multi-agent systems. Based on the feature of heterogeneous agents, a novel protocol is proposed for heterogeneous multi-agent systems. First, the state transformation method is used and an equivalent system is obtained. Then, the group consensus problem is analysed and some sufficient and/or necessary conditions are given for heterogenous multi-agent systems under undirected and directed networks, respectively. Finally, simulation examples are presented to demonstrate the effectiveness of the theoretical results.     

Hierarchical architectures in structured peer-to-peer overlay networks

Distributed Hash Tables (DHT) are presently used in several large-scale systems in the Internet and envisaged as a key mechanism to provide identifier-locator separation for mobile hosts in Future Internet. Such P2P-based systems become increasingly complex serving popular social networking, resource sharing applications, and Internet-scale infrastructures. Hierarchy is a standard mechanism for coping with heterogeneity and scalability in distributed systems. To address the shortcomings of flat DHT designs, many hierarchical P2P designs have been proposed over recent years. The last generation is hierarchical DHTs (HDHTs) where nodes are organized onto layers and groups. This article discusses hierarchical architectures applied in structured P2P overlay networks, focusing on HDHT designs. We introduce a framework consisting of conceptual models of network hierarchy, multi-layer hierarchical DHT architectures, principles affecting the design choices, and cost models for system tradeoff analysis, performance evaluation, and scalability estimation. Based on the framework we provide a taxonomy and survey more than 20 hierarchical HDHT proposals.     

A peer-to-peer file search and download protocol for wireless ad-hoc networks

Deployment of traditional peer-to-peer file sharing systems on a wireless ad-hoc network introduces several challenges. Information and workload distribution as well as routing are major problems for members of a wireless ad-hoc network, which are only aware of their immediate neighborhood. In this paper, we propose a file sharing system that is able to answer location queries, and also discover and maintain the routing information that is used to transfer files from a source peer to another peer. We present a cross-layer design, where the lookup and routing functionality are unified. The system works according to peer-to-peer principles, distributes the location information of the shared files among the members of the network. The paper includes a sample scenario to make the operations of the system clearer. The performance of the system is evaluated using simulation results and analysis is provided for comparing our approach with a flooding-based, unstructured approach.     

A gradient flow approach to on-line robust pole assignment for synthesizing output feedback control systems

Pole assignment is a basic design method for synthesis of feedback control systems. In this paper, a gradient flow approach is presented for robust pole assignment in synthesizing output feedback control systems. The proposed approach is shown to be capable of synthesizing linear output feedback control systems via on-line robust pole assignment. Convergence of the gradient flow can be guaranteed. Moreover, with appropriate design parameters the gradient flow converges exponentially to an optimal solution to the robust pole assignment problem and the closed-loop control system based on the gradient flow is globally exponentially stable. These desired properties make it possible to apply the proposed approach to slowly time-varying linear control systems. Simulation results are shown to demonstrate the effectiveness and advantages of the proposed approach.     

A contribution-based service differentiation scheme for peer-to-peer systems

Trust is required in a file sharing peer-to-peer system to achieve better cooperation among peers. In reputation-based peer-to-peer systems, reputation is used to build trust among peers. In these systems, highly reputable peers will usually be selected to upload requested files, decreasing significantly malicious uploads in the system. However, these peers need to be motivated by increasing the benefits that they receive from the system. In addition, it is necessary to motivate free riders to contribute to the system by sharing files. Malicious peers should be also motivated to contribute positively by uploading authentic files instead of malicious ones. Service differentiation is required to motivate peers to get involved by sharing and uploading the requested files. To provide the right incentives for peers to contribute to the system, the new concept of Contribution Behavior is introduced for partially decentralized peer-to-peer systems. In this paper, the Contribution Behavior of the peer is used as a guideline for service differentiation instead of peer’s reputation. Both Availability and Involvement of the peer are used to assess its Contribution Behavior. Performance evaluations confirm the ability of the proposed scheme to effectively identify both free riders and malicious peers and reduce the level of service provided to them. On the other hand, good peers receive better service. Simulation results also confirm that based on a Rational Behavior, peers are motivated to increase their contribution to receive services. Moreover, using our scheme, peers must continuously participate, reducing significantly the milking phenomenon.

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.     

Reducing communication costs in robust peer-to-peer networks

Several recent research results describe how to design Distributed Hash Tables (DHTs) that are robust to adversarial attack via Byzantine faults. Unfortunately, all of these results require a significant blowup in communication costs over standard DHTs. For example, to perform a lookup operation, all such robust DHTs of which we are aware require sending O(log³n) messages while standard DHTs require sending only O(logn), where n is the number of nodes in the network. In this paper, we describe protocols to reduce the communication costs of all such robust DHTs. In particular, we give a protocol to reduce the number of messages sent to perform a lookup operation from O(log³n) to O(log²n) in expectation. Moreover, we also give a protocol for sending a large (i.e. containing Ω(log⁴n) bits) message securely through a robust DHT that requires, in expectation, only a constant blowup in the total number of bits sent compared with performing the same operation in a standard DHT. This is an improvement over the O(log²n) bit blowup that is required to perform such an operation in all current robust DHTs. Both of our protocols are robust against an adaptive adversary.     

HyperTree for self-stabilizing peer-to-peer systems

Peer-to-peer systems are prone to faults; Therefore, it is extremely important to design peer-to-peer systems that automatically regain consistency or, in other words, are self-stabilizing. In order to achieve the above, we present a deterministic structure that defines the entire (IP) pointers structure among the machines, for every n machines; i.e., defines the next hop for the insert, delete, and search procedures of the peer-to-peer system. Thus, the consistency of the system is easily defined, monitored, verified, and repaired. We present the HyperTree (distributed) structure, which supports the peer-to-peer procedures while ensuring that the out-degree and the in-degree (the number of outgoing/ incoming pointers) are b log _b n where n is the actual number of machines and b is an integer parameter greater than 1. Moreover, the HyperTree ensures that the maximal number of hops involved in each procedure is bounded by log _b n. A self-stabilizing peer-to- peer distributed algorithm based on the HyperTree is presented. This work was partially supported by IBM Faculty Award, NSF Grant 0098305, the Israeli Ministry of Trade and Industry, the Rita Altura Trust Chair in Computer Sciences and the Lynne and William Frankel Center for Computer Sciences. The work was done while Ronen I. Kat was a PhD student at Ben-Gurion University of the Negev. An preliminary version was published in the proceedings of the third IEEE International Symposium on Network Computing and Applications (NCA’04).     

一种新的间歇过程鲁棒在线监控方法

多向主元分析(MPCA)的统计监控模型,因为易受建模数据中离群点的影响,还需预估新批次未反应完的数据,所以提出一种新的间歇过程鲁棒在线监控法。先利用改进尺度的CDC/MVT算法获取常规建模的批次数据;再用多模型非线性结构代替传统的MPCA单模型线性化结构,并提出确定时滞变量的算法。前者用于监控β-甘露聚糖酶发酵批过程,并与移动窗多向主元分析(MWMPCA)法相比,即使建模数据中存在离群点,前者仍能获得正确的监控结果,减少建模时对数据的要求;同时克服了MPCA不能处理实时性的问题,避免了MPCA在线应用时预测值的误差;更能精确描述过程的故障,准确性和实时性良好。     

A robust model for on-line handwritten japanese text recognition

This paper describes a robust context integration model for on-line handwritten Japanese text recognition. Based on string class probability approximation, the proposed method evaluates the likelihood of candidate segmentation–recognition paths by combining the scores of character recognition, unary and binary geometric features, as well as linguistic context. The path evaluation criterion can flexibly combine the scores of various contexts and is insensitive to the variability in path length, and so, the optimal segmentation path with its string class can be effectively found by Viterbi search. Moreover, the model parameters are estimated by the genetic algorithm so as to optimize the holistic string recognition performance. In experiments on horizontal text lines extracted from the TUAT Kondate database, the proposed method achieves the segmentation rate of 0.9934 that corresponds to a f-measure and the character recognition rate of 92.80%.     

Dependability in peer-to-peer systems

Server-centric architectures such as the Web's suffer from well-known problems related to application size and increasing user requests. Peer-to-peer systems can help address some of the key challenges, but this survey of several current P2P systems shows that dependability remains an open issue. To perform in Internet-scale applications, P2P systems must address the four major properties of dependable systems: scalability, fault-tolerance, security, and anonymity. An output of the comparison provided is an attempt to move toward common terms and definitions. Because the models underlying current P2P systems must be understood to support a thorough investigation of dependability properties, we briefly examine the most popular P2P systems and then compare how these systems address dependability.     

A novel DRM framework for peer-to-peer music content delivery

Due to rapid advances in the network communications field in recent years, the distribution of large-scale music contents has become easier and more efficient than ever before. However, the unauthorized distribution of copyright-protected content has emerged as a major concern. Accordingly, this paper presents a content distribution framework with a DRM capability for P2P networks. The robustness of the content distribution is ensured by using a network coding approach based on the Lagrange polynomial interpolation method. When the downloading peer within the network receives sufficient coded pieces, it not only reconstructs the associated blocks using a finite field Gaussian elimination method, but also creates its own copies of the coded pieces within these blocks and shares these copies amongst the other peers in the network. As a result, the distribution overhead imposed on the music provider is substantially reduced and the number of coded pieces within the network is significantly increased, thereby overcoming the “last piece problem” inherent in existing P2P schemes. In the DRM module of the framework, the RSA public-key cryptosystem is used to generate a unique digital fingerprint for every user within the network. The fingerprint is embedded within the music file in a protected form such that the music provider can establish the identification of any user performing an unauthorized distribution of the file. The experimental results confirm that the proposed framework provides an efficient and secure means of distributing large-scale copyright-protected music contents with no discernible degradation in the audio quality.     

A novel state cache scheme in structured P2P systems

Large-scale P2P systems typically have hundreds of thousands of peers that involve frequent dynamic activities. Current structured overlays do not identify well the rhythm in the dynamic activities, thus resulting in high maintenance overhead. In this paper, we present a new state cache system, called SCS, that solves the problem by exploiting the access patterns of dynamic activities in P2P systems. SCS partitions the whole P2P network into clusters and dynamically chooses a “super” node in each cluster to selectively record and maintain the routing information for departed nodes most likely to arrive back in the near future. The cached routing information enables SCS to simplify self-organization, reduce system maintenance overhead and provide high quality routing service. The experimental results show that SCS reduces the maintenance overhead by up to 66% while delivering much better routing performance, as compared to current structured P2P systems.     

一种WSNs中的强实体认证协议

无线传感器网络(WSNs)由于其部署环境的开放性、资源的有限性等特点,比传统网络更易受到安全方面的威胁,其安全问题变得极为重要。针对WSNs中的认证机制的效率和安全问题,提出了一种有效的强实体认证协议。通过采用秘密共享方案,通过多个节点对用户进行认证,能够有效地防止非法用户加入网络。通过实验分析和对比表明:协议既能满足网络对安全的需求,又能最大程度地节约传感器节点的能量。     

SLACER: a self-organizing protocol for coordination in peer-to-peer networks

Coordination between nodes in open distributed computer systems is a general problem that's becoming increasingly relevant as massive peer-to-peer (P2P) systems are being deployed on the Internet. A major subproblem is establishing and maintaining cooperation between nodes. To solve this problem, we created a simple algorithm, SLACER (a selfish link-based adaptation for cooperation excluding rewiring). When executed in a P2P network's nodes, SLACER self-organizes the network into a robust artificial social network (ASN) with small-world characteristics and high cooperation.