P2P技术原理及应用

对等网络(P2P)有3种主要的组织结构:分布式哈希表(DHT)结构、树形结构、网状结构。P2P技术已经延伸到几乎所有的网络应用领域,如分布式科学计算、文件共享、流媒体直播与点播、语音通信及在线游戏支撑平台等方面。现在人们已经开始将重心转入到覆盖层网络的节点延时聚集研究、覆盖网之间(Inter-Overlay)优化研究、P2P支撑平台研究以及P2P安全研究等方面。     

面向用户需求的信息服务模型

针对广域网络环境下面向用户需求的信息服务要求,给出了一个面向用户信息需求的信息服务模型,并对该模型进行了形式化描述,在此基础上设计了一种基于语义覆盖网络的信息服务体系框架。该框架充分考虑用户的信息需求与信息体系,提供了一种趋于扁平化的信息共享与服务环境。该框架通过自底向上和自顶向下相结合的信息组织模式,基于语义覆盖网络提供信息资源发布、发现与定位的能力。     

Host Mobility Using an Internet Indirection Infrastructure

We propose the Robust Overlay Architecture for Mobility (ROAM) to provide seamless mobility for Internet hosts. ROAM is built on top of the Internet Indirection Infrastructure (i3). With i3, instead of explicitly sending a packet to a destination, each packet is associated with an identifier. This identifier defines an indirection point in i3, and is used by the receiver to obtain the packet. ROAM takes advantage of end-host ability to control the placement of indirection points in i3 to provide efficient routing, fast handoff, and preserve location privacy for mobile hosts. In addition, ROAM allows end hosts to move simultaneously, and is as robust as the underlying IP network to node failure. We have developed a user-level prototype system on Linux that provides transparent mobility without modifying applications or the TCP/IP protocol stack. Simulation results show that ROAM's latency can be as low as 0.25–40% of Mobile IP. Experimental results show that with soft handoff the TCP throughput decreases only by 6% when there are as many as 0.25 handoffs per second. Shelley Zhuang received the B.S. degree in computer engineering and computer science from the University of Missouri-Columbia in 1999, and is now pursuing her Ph.D. degree in computer science at University of California-Berkeley. She has interned at NASA Goddard Space Flight Center, Microsoft, and DaimlerChrysler Research and Technology North America. Her research interest include overlay networking, content distribution networks, streaming media, multicast routing, wireless communications, and network security. Kevin Lai is currently a Scientist at HP Labs. He received his A.B. in Computer Science from U.C.Berkeley and his Ph.D. in Computer Science from Stanford University. Previously he was a post-doctoral scholar in the School of Information Management and Systems (SIMS) and EECS Department at U.C. Berkeley. He has worked on operating systems, mobility, ad hoc networking, network measurement, and incentive systems Ion Stoica received his PhD from the Carnegie Mellon University in 2000. He is an Assistant Professor in the EECS Department at University of California at Berkeley, where he does research on resource management, scalable solutions for end-to-end quality of service, and peer-to-peer network technologies in the Internet. Stoica is the recipient of a Sloan Foundation Fellowship (2003, a National Science Foundation CAREER Award (2002), the ACM doctoral dissertation award (2001), and an Okawa Foundation Fellowship (2001). He is a member of ACM. Randy Howard Katz received his undergraduate degree from Cornell University, and his M.S. and Ph.D. degrees from the University of California, Berkeley. He joined the faculty at Berkeley in 1983, where he is now the United Microelectronics Corporation Distinguished Professor in Electrical Engineering and Computer Science. He is a Fellow of the ACM and the IEEE, and a member of the National Academy of Engineering. He has published over 200 refereed technical papers, book chapters, and books. His hardware design textbook, Contemporary Logic Design, has sold over 85,000 copies worldwide, and has been in use at over 200 colleges and universities. He has supervised 35 M.S. theses and 21 Ph.D. dissertations, and leads a research team of over a dozen graduate students, technical staff, and industrial visitors. He has won numerous awards, including seven best paper awards, one “test of time" paper award, one paper selected for a 50 year retrospective on IEEE communications publications, three best presentation awards, the Outstanding Alumni Award of the Computer Science Division, the CRA Outstanding Service Award, the Berkeley Distinguished Teaching Award, the Air Force Exceptional Civilian Service Decoration, the IEEE Reynolds Johnson Information Storage Award, the ASEE Frederic E. Terman Award, and the ACM Karl V. Karlstrom Outstanding Educator Award. With colleagues at Berkeley, he developed Redundant Arrays of Inexpensive Disks (RAID), a $ 25 billion per year industry sector today. While on leave for government service in 1993–1994, he established whitehouse.gov and connected the White House to the Internet. His current research interests are Internet Services Architecture, Mobile Internet, and the technologies underlying the convergence of telecommunications and packet networks. Prior research interests have included: database management, VLSI CAD, and high performance multiprocessor and storage architectures. Scott Shenker received his degrees, in theoretical physics, from Brown University (Sc. B.) and the University of Chicago (Ph. D.). After a postdoctoral year at Cornell's physics department in 1983, he joined Xerox's Palo Alto Research Center. He left PARC in 1999 to head up a newly established Internet research group at the International Computer Science Institute (ICSI) in Berkeley. Scott's research over the past 15 years has spanned the range from computer performance modeling and computer networks to game theory and economics. Most of his recent work has focused on the Internet architecture and related issues.     

An Enquiry-Based Dynamic Service Provisioning Approach for Overlay IP-over-Optical Networks

Network control for IP-over-optical networks can be classified as falling under the overlay, augmented, or peer models. In the first two models, the IP layer and the optical layer only have the resource information of their respective layers. In the peer model, all the resource information is known to both layers; hence, it can potentially achieve better resource utilization. Unfortunately, the peer model approach is generally not acceptable to the operators if the IP layer and optical layer belong to two different administrations. In addition, it is much more complex and generally seen as not feasible in the near future In this paper, we propose an enquiry-based provisioning scheme based on the overlay model which can, however, utilize resources in both layers as in the peer model approach. Two simple and novel algorithms for routing labeled-switched path (LSP) requests for this provisioning scheme are proposed. Simulation results show that our proposed algorithms perform significantly better than other routing algorithms for the overlay model and are nearly as good as the integrated routing algorithm for the peer model.     

物流中心选址的多目标优化模型

针对一个经纬型网络中的最优选址问题,借鉴选址问题的已有理论和方法,建立了一个新的数学模型.研究了该模型的实际可行算法,结果表明该算法所求解是最优的,为运输、供销、物流系统的实际部门提供了有效的方法.     

System‐Level Performance of Spread Spectrum‐Based Add‐on Service Overlaid onto the Existing Terrestrial Digital Multimedia Broadcast Band

We consider an overlaid broadcast service, where a spread spectrum (SS)‐based broadcast signal is overlaid onto the existing terrestrial Digital Multimedia Broadcasting (T‐DMB) band. The system is similar to the augmented data transmission in the ATSC DTV, for which it was investigated mostly in terms of link level performance, such as bit error rate. Our focus in this paper is on the system‐level performances. More specifically, utilizing both a large scale path loss and a small scale fading channel model, the primary objective is to explore the tradeoff between the coverage and the achievable rate of the overlaid service and, finally, to determine the achievable rate in the overlaid service for marginal coverage reduction in the existing broadcast service. The analytical and simulation results show that an SS‐based add‐on service of 10 kbps to 20 kbps can co‐exist with the T‐DMB service while resulting in only a marginal degradation in T‐DMB coverage (for example, less than one percent reduction).     

MMSE RAKE Reception for Asynchronous DS/CDMA Overlay Systems and Frequency-Selective Fading Channels

In this work the authors introduce and analyze a detection scheme for simultaneous suppression ofmultiaccess and digital narrowband interference (NBI) for an asynchronousDS/CDMA system operatingover a frequency-selective fading channel. The proposed detector may possibly consider a processing interval greater than the bit-interval, andamounts to a RAKE structure, wherein each branch is designed under an MMSE optimization strategy, followedby a propercombining rule. It is shown that narrowband interference rejection entails ingeneral a time-varyingdetection structure. As to the performance assessment, we give closed-form formulas for the systemBit Error Rate (BER),Near-Far Resistance and Signal-to-Interference Ratio (SIR).Numerical results show that the proposed receiver proves effective in suppressing interference, and that itlargely outperforms conventional multiuser detectors which do not account forthe presence of theNBI, at the price of little complexity increase.Finally, we provide a blind adaptive implementation of the proposedreceiver, based on the exponentially weighted Recursive-Least-Squares (RLS)algorithm, andrequiring knowledge of the relevant parameters of the desired user only, andof the NBI signaling time.     

Space-Time Optimum Combining for CDMA Overlay for Personal Communications Systems

The requirement to suppress narrowband interferences in CDMA communication stems from the overlay concept, i.e., coexistence of different types of signals in the same frequency band. This paper describes the performance analysis of a direct-sequence (DS) CDMA personal communication system sharing a common spectrum with narrowband microwave radio links in the 1.85 to 1.99 GHz band. The coexistence of these two systems within the same frequency band will improve the overall spectrum efficiency, but will also cause interference to both systems. In this paper it is shown that joint spatial and temporal optimum combining provides an efficient means of improving the performance of the DS-CDMA system through cancellation of the narrowband signal and the co-channel interferences. The proposed space-time architecture provides degrees of freedom for both diversity and interference cancellation. It is shown that the joint space-time receiver is robust with respect to the narrowband interference signal bandwidth and its carrier frequency offset from the DS-CDMA carrier frequency.     

西南某水电站谷底深厚覆盖层与卸荷松弛带特征及其成因机制分析

钻孔揭示,该水电站河谷谷底发育着深厚覆盖层及卸荷松弛带。深厚覆盖层纵向上可以分为3层:下部和上部为正常的河流相,中部为多成因堆积物加积层;谷底浅表部岩体结构松弛,完整性差,裂隙张开、泥质充填,裂面严重风化锈染。研究表明,谷底松弛是由于河流切至谷底时造成应力集中,导致岩体剪切破坏;并经过漫长的卸荷回弹及风化作用在谷底形成一定厚度的松弛带。     

二元有理插值的迭加算法

在已有基础上给出一种新的算法,即迭加插值算法,并给出相应的插值有理函数的具体表达式,以及与已有算法比较,该算法具有较大的灵活性,更便于实际应用.