Anonymity analysis of P2P anonymous communication systems

Compared with traditional static Client/Server architecture, the P2P architecture is more suitable for anonymous communication systems because it is more flexible and can keep load balance better. However, in order to make the system usable and reliable, some system designs make tradeoffs between anonymity and performance such as reliability, latency and throughput. Tradeoffs are sometimes unavoidable in system design, but which tradeoffs are acceptable and which are not is very important for developers. This paper models the P2P anonymous communications and takes quantitative analysis of anonymity by information theory with entropy. Based on this analysis, it studies the effect of key system design strategies on anonymity in network architecture, routing and message relay, and measures which strategies should be used in anonymous communications and which are unreasonable. Some analysis results are contrary to our intuition. For example, it quantitatively concludes that in some cases the anonymity is not enhanced when the system scale increases, and too long an anonymous tunnel may not provide higher anonymity but lowers performance. These analysis results are valuable for developers of P2P anonymous communication systems. Besides, this paper also discusses some possible strategies such as trust and reputation to enhance the P2P anonymous communications.     

TRPC-UWB通信系统基于不同调制方式的性能分析

为了克服传统TR系统因延迟线过长而在实际中难以实现的问题,传输参考脉冲簇(Transmitted Reference Pulse Cluster,TRPC)系统作为传输参考(Transmitted Reference,TR)系统的一种改进方案,成为一种颇具潜力的非相干超宽带(Ultra-WideBand,UWB)通信系统。TRPC系统最初采用二进制相移键控(Binary Phase Shift Keying,BPSK)的调制方式,虽然基于这种调制方式的TRPC系统性能已明显优于传统TR,但是为了满足不同应用场合在复杂度及成本方面的要求,有必要进一步研究多种调制方式在TRPC系统中的性能。因此,以OOK、BPSK-PPM及BPSK三种调制方式为研究对象,分析、比较它们在TRPC系统中的性能。理论分析以及MATLAB仿真结果表明,在实现TRPC系统时,需要根据复杂度、成本及误码性能等方面的要求选择合适的调制方式。     

Penalized cluster analysis with applications to family data

The goal of cluster analysis is to assign observations into clusters so that observations in the same cluster are similar in some sense. Many clustering methods have been developed in the statistical literature, but these methods are inappropriate for clustering family data, which possess intrinsic familial structure. To incorporate the familial structure, we propose a form of penalized cluster analysis with a tuning parameter controlling the tradeoff between the observation dissimilarity and the familial structure. The tuning parameter is selected based on the concept of clustering stability. The effectiveness of the method is illustrated via simulations and an application to a family study of asthma.     

混沌Ikeda系统同步及其在保密通信中的应用

针对一类时滞Ikeda混沌系统,利用Lyapunov稳定和微分不等式,研究了其指数同步问题。基于线性矩阵不等式理论得到了指数同步的充分条件,给出了指数同步控制器的设计方法,利用混沌掩盖将该同步方法应用于保密通信。仿真表明,该方案具有同步速度快、鲁棒性良好等优良性能。     

Teletraffic analysis of cellular communication systems with general mobility based on hyper-Erlang characterization

This paper proposes a new analytical model for the performance evaluation of cellular communication systems. Our model allows more general cases of the distributions of the call time and the cell residence time. Based on the characterization of the call time by a hyper-Erlang distribution, the Laplace transform of the channel occupancy time distribution is derived as a function of the Laplace transform of the cell residence time distribution. In particular, the essential quality of service measure such as the forced termination probability is exactly obtained by using a delayed renewal process. From numerical results, it is shown that the non-exponential model has an obvious difference in performance as compared to exponential models.     

认证技术及其在移动通信系统中的应用

总结了认证技术的基本原理,重点分析了现有的几种移动通信系统所采用的认证机制的安全性,给出了移动通信系统中认证机制的发展方向。     

Impulsively synchronizing chaotic systems with delay and applications to secure communication

In this paper, the presence of transmission delay and sampling delay in chaos-based secure communication systems by employing impulsive synchronization is studied. A time delayed impulsive differential system with delayed impulses, modeling the synchronization error between the driving and response schemes employed in such communication systems, is presented. The equi-attractivity property of the error dynamics is investigated and the sufficient conditions leading to this property are obtained. A set of upper bounds on the delay terms involved in the system are also obtained, and a numerical example is given. A communication security scheme employing hyperchaotic systems possessing continuous driving, impulsive driving and delay is proposed and simulation results are given to demonstrate the performance of the scheme.     

Enhancing throughput for streaming applications running on cluster systems

The exploitation of throughput in a parallel application that processes an input data stream is a difficult challenge. For typical coarse-grain applications, where the computation time of tasks is greater than their communication time, the maximum achievable throughput is determined by the maximum task computation time. Thus, the improvement in throughput above this maximum would eventually require the modification of the source code of the tasks. In this work, we address the improvement of throughput by proposing two task replication methodologies that have the target throughput to be achieved as an input parameter. They proceed by generating a new task graph structure that permits the target throughput to be achieved. The first replication mechanism, named DPRM (Data Parallel Replication Mechanism), exploits the inner task data parallelism. The second mechanism, named TCRM (Task Copy Replication Mechanism), creates new execution paths inside the application task graph structure that allows more than one instance of data to be processed concurrently. We evaluate the effectiveness of these mechanisms with three real applications executed in a cluster system: the MPEG2 video compressor, the IVUS (Intra-Vascular Ultra-Sound) medical image application and the BASIZ (Bright and SAtured Images Zone) video processing application. In all these cases, the obtained throughput was greater after applying the proposed replication mechanism than what the application could provide with the original implementation.     

Cell communication in tissue P systems: universality results

We introduce an evolution-communication model for tissue P systems where communication rules are inspired by the general mechanism of cell communication based on signals and receptors: a multiset can enter a cell only in the presence of another multiset. Some basic variants of this model are also considered where communication is restricted either to be unidirectional or to use special multisets of objects called receptors. The universality for all these variants of tissue P systems is then proved by using two cells (three cells in the case of unidirectional communication) and rules of a minimal size.     

The power of communication: P systems with symport/antiport

In the attempt to have a framework where the computation is done by communication only, we consider the biological phenomenon of trans-membrane transport of couples of chemicals (one say symport when two chemicals pass together through a membrane, in the same direction, and antiport when two chemicals pass simultaneously through a membrane, in opposite directions). Surprisingly enough, membrane systems without changing (evolving) the used objects and with the communication based on rules of this type are computationally complete, and this result is achieved even for pairs of communicated objects (as encountered in biology). Five membranes are used; the number of membranes is reduced to two if more than two chemicals may collaborate when passing through membranes. Andrei Paun: He graduated the Faculty of Mathematics of Bucharest University in 1998, received his M.Sc. degree from The University of Western Ontario in 1999, and since then he is a PhD student in the Computer Science Department of University of Western Ontario, London, Canada (under the guidance of prof. Sheng Yu). The topic of his thesis is Molecular Computing (especially, DNA and Membrane Computing), but his research interests also include neural networks, implementing automata, combinatorics on words. Gheorghe Paun: (the proud father of two sons, including the first author of this paper) He is a member of the Romanian Academy, working as a senior researcher in the Institute of Mathematics of the Romanian Academy, Bucharest, and as a Ramon y Cajal researcher in Rovira i Virgili University of Tarragona, Spain. He is one of the most active authors in (the theory of) DNA Computing, (co)author of many papers in this area, (co)author and (co)editor of several books. In 1998 he has initiated the area of Membrane Computing. Other research interests: regulated rewriting, grammar systems, contextual grammars, combinatorics on words, computational linguistics.     

基于簇域的P2P信誉评估模型

针对现有的信任模型的网络消耗大、信任数据存储和查询等问题,设计了一种基于簇域的P2P网络拓扑结构的信誉评估模型P2P-Crep.模型采用双层网络拓扑结构,解决信任数据的存储和查询及网络消耗问题.通过对信誉模型的性能分析和仿真试验,验证了模型的动态性、可扩展性以及对电子商务恶意行为的有效抵制.     

An architecture for attacking the communication bottleneck in P systems

The distributed implementation of P systems on a cluster of processors has met with a bottleneck communications problem. When the number of membranes grows in the system, the network gets congested and the time taken to execute an evolution step degrades. In this article, we suggest a software architecture denominated “partially parallel evolution with partially parallel communication”, where some membranes are located in each processor, proxies are used to communicate with membranes located in different processors, and a policy of access control to the communications network is mandatory. With all this, we get a certain parallelism in the system and an acceptable functioning in communications. In addition to this, it establishes a series of equations that allows us to determine in the architecture the optimum number of processors needed, the time required to execute an evolution step, the number of membranes to be located in each processor, and the conditions to determine when it is best to use the distributed solution or the sequential one. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

A session key caching and prefetching scheme for secure communication in cluster systems

With the widespread use of cluster systems and ever increasing threat to computer security, it becomes more necessary to design and build secure cluster systems. Most cluster systems rely on security products like firewalls for their security, but they cannot guarantee security of intra-cluster communications, which can be a weak spot that hackers exploit for further security attacks. A recent study by Lee and Kim (2007) [22] proposed a security framework to protect intra-cluster communications by encrypting and authenticating all packets with fine-grained security where any two communicating processes dynamically generate and share a cryptographic key, called a session key. However, the fine-grained security scheme can incur serious performance degradation in large-scale cluster systems since it may take a long time to access session keys. To solve this problem, we propose to incorporate a session key cache inside a cluster interconnect card to speed up accesses to the session keys and build an analytical cluster traffic model to estimate the behavior of the cache in large-scale cluster systems. For further performance improvement, we propose a prefetching scheme speculating job scheduler’s decision without OS interventions. Simulation results indicate that the session key cache with the prefetching scheme decreases the network latency by 50% on average, compared to the configurations without the enhancements.     

基于蓝牙Piconet的LEGO多机器人P2P通信

P2P通信是构建复杂多机器人系统的基础,由于LEGO NXT资源有限,不适于采用常用的Scatternet机制实现P2P通信。以支持蓝牙设备的PC作为中控机和网络主设备,基于Piconet,在中控机上提供可以接收/缓存/转发来自各NXT的通信数据,通过封装,在逻辑上形成P2P通信网络。协同舞蹈4机器人系统原型的研制工作验证了该组网通信机制可行。     

基于网络环境感知的P2P通信方案设计

为解决当前各种P2P方案的局限性,提高P2P通信的效率,针对P2P通信网络环境的复杂性,提出了一种具有网络环境感知能力的P2P通信方案并予以实现。该方案借助中间服务器能对P2P客户所处的网络环境进行感知并在两个P2P客户之间采用最优的通信方案进行通信。通过Vmware软件搭建了实验环境,并对各种拓扑下的方案性能进行实验模拟。实验结果表明,相对于其它常用的P2P通信方案,该方案的会话具有更高的会话建立连接率,而且具有更少的信令开销,同时具有更优的端到端延时性能,证明了提出的方案优于其它方案。     

On necessary conditions for scale-freedom in complex networks,with applications to computer communication systems

Many complex networks exhibit a scale-free, power-law distribution of vertex degrees. This common feature is a consequence of two generic mechanisms relating to the formation of real networks: (i) networks tend to expand over time through the addition of new vertices and (ii) new vertices attach preferentially to those that are already well connected. We show that for many natural or man-made complex networks possessing a scale-free power-law distribution with the exponent γ ≥ 2, the number of degree-1 vertices, when nonzero, is of the same order as the network size N and that the average degree is of order at most log N. Our results expose another necessary characteristic of such networks. Furthermore, our method has the benefit of relying only on conditions that are static and easily verified for arbitrary networks. We use the preceding results to derive a closed-form formula approximating the distance distribution in scale-free networks. Such distributions are applied extensively in the fields of computer communication and software architecture, among other domains.     

基于通信范围约束的传感器网络多层分簇算法

无线传感器网络设计的一个主要目标就是最大化网络生命期,因此需要研究如何部署适当数量的簇头节点达到最小化整个网络节点数据传输能量消耗。针对这种问题,提出了一种基于通信范围约束的多层簇类算法（HCRC）,基于单层次的数据融合结构,给出了多层次的数据融合,然后对每一层簇头通过通信范围选择父节点,减少数据包传输次数。仿真结果表明：该协议能显著减少整个无线网络能量消耗,保证能量消耗少、网络拓扑结构可变的条件下,具有较好的实用性和鲁棒性。     

State-based real-time analysis of SDF applications on MPSoCs with shared communication resources

The timing predictability of Multi-Processor System on Chip (MPSoC) platforms with hard real-time applications is much more challenging than that of traditional platforms due to their large number of shared processing, communication and memory resources. Yet, this is an indispensable challenge for guaranteeing their safe usage in safety critical domains (avionics, automotive).In this article, a real-time analysis based on model-checking is proposed. The model-checking based method allows guaranteeing timing bounds of multiple Synchronous Data Flow Application (SDFA) implementations. This approach utilizes timed automata (TA) as a common semantic model to represent WCET of software components (SDF actors) and shared communication resource access protocols for buses, DMA, private local and shared memories of the MPSoC. The resulting network of TA is analyzed using the UPPAAL model-checker for providing safe timing bounds of the implementation. Furthermore, we will show the extension of our previous system model enabling single-beat inter-processor communication style beside the burst-transfer style and provide the implementation of the complete set of TA templates capturing the considered system model.We demonstrate our approach using a multi-phase electric motor control algorithm (modeled as SDFA) mapped to Infineon’s TriCore-based Aurix multicore hardware platform with both the burst and single-beat inter-processor communication styles. Our approach shows a significant precision improvement (up to a percentage improvement of 300%) compared with the worst-case bound calculation based on a pessimistic analytical upper-bound delays for every shared resource access. In addition, scalability is examined to demonstrate analysis feasibility for small parallel systems, up to 40 actors mapped to 4-tiles and up to 96 actors on a 2-tiles platforms.