IP网络性能指标体系的研究

网络性能指标是网络测评的基础。本文从网络测评的不同角度对IP网络的性能指标进行了综合分析，指出了一种能系统反映IP网络性能的指标体系，并给出了IP网络性能指标体系的形式描述。在此基础上引入了泛化指标和确定性指标的概念，探讨了确定性指标的内容有及描述框架。该研究突破了目前IP网络性能指标体系研究的简单性、局限性，对IP网络测试和性能评价具有指导意义。     

A framework for optimizing the cost and performance ofnext-generation IP routers

The explosive growth of Internet users, the increased user demand for bandwidth, and the declining cost of technology have all resulted in the emergence of new classes of high-speed distributed IP-router architectures with packet-forwarding rates of the order of gigabits, or even terabits, per second. This paper develops an analytical framework for modeling and analyzing the impact of technological factors on the cost-performance tradeoffs in distributed-router architectures. The main tradeoff in a distributed router results naturally from moving the main packet-forwarding and processing power from a centralized forwarding engine to an ensemble of smaller forwarding engines, either dedicated to or shared among the line cards. Processing packets in these smaller engines can be much cheaper (by as much two to three orders of magnitude) than in a centralized forwarding engine. Therefore, the main goal of our modeling framework is to determine an optimal allocation of processing power to the forwarding engines (in a distributed router) to minimize overall router cost while achieving a given level of packet-forwarding performance. Two types of router models are analyzed using the proposed framework: a distributed-router architecture and parallel-router architecture     

Architectures and performance of AWG-based optical switching nodes for IP networks

In order to support the continuous growth of transmission capacity demand, optical packet switching technology is emerging as a strong candidate, promising to allow fast dynamic allocation of wavelength-division multiplexing (channels, combined with a high degree of statistical resource sharing). This work addresses the design of optical switch architectures, based on previous proposals available in the technical literature that use an arrayed waveguide grating (AWG) device to route packets. Since the port number of currently available AWGs is a limiting factor, we propose two new modified structures which better exploit the switching capability of this component in the wavelength domain. Since a limited hardware complexity is a key requirement for all-optical switches, due to the high cost of optical components, these different node configurations are compared in terms of complexity. Traffic performance of these new structures in a full optical packet switching scenario is also examined.     

Architectures and performance of optical packet switching nodes for IP networks

As new bandwidth-hungry Internet protocol (IP) services are demanding more and more capacity, transport networks are evolving to provide a reconfigurable optical layer in order to allow fast dynamic allocation of wavelength-division-multiplexing (WDM) channels. To achieve this goal, optical packet-switched systems seem to be strong candidates as they allow a high degree of statistical resource sharing, which leads to an efficient bandwidth utilization. In this paper, we propose an architecture for optical packet-switched transport networks, together with an innovative switching node structure based on the concept of per-packet wavelength routing. The traffic performance of such node when loaded by a typical IP traffic is evaluated through computer simulation; packet loss probability and average delay performance are shown for various load conditions.     

A multilayer IP security protocol for TCP performance enhancement in wireless networks

Transmission control protocol (TCP) performance enhancement proxy (PEP) mechanisms have been proposed, and in some cases widely deployed, to improve TCP performance in all-Internet protocol (IP) wireless networks. However, this technique is conflicted with IP-security (IPsec)-a standard IP security protocol that will make inroad into wireless networks. This paper analyzes the fundamental problem behind this conflict and develops a solution called multilayer IP-security (ML-IPsec). The basic principle is to use a multilayer protection model and a fine grain access control to make IP security protocols compatible with TCP PEP. It allows wireless network operators or service providers to grant base stations or wireless routers limited and controllable access to the TCP headers for performance enhancement purposes. Through careful design, implementation, and evaluation, we show that we can easily add ML-IPsec to existing IPsec software and the overhead is low. We conclude that ML-IPsec can help wireless networks provide both security and performance.     

Study on a joint multiple layer restoration scheme for IP over WDM networks

In this article we investigate the problem of a restoration scheme for IP over WDM networks. Network reliability is gaining importance with the huge volume of traffic carried by such networks. Providing survivability at the optical layer is inherently attractive, but raises many questions and challenges, given the characteristic of optical aggregated lightpath and relatively coarse traffic granularity. The emergence of MPLS and its extension, MP/spl lambda/S, opens up new possibilities for developing simple integrated protection/restoration schemes that can be coordinated at both the IP and optical layers . This article first presents an overview of existing MPLS/MP/spl lambda/S recovery mechanisms. Then we propose a joint two-layer recovery scheme for IP-centric WDM-based optical networks where the optical layer takes the recovery actions first, and subsequently the upper IP layer initiates its own recovery mechanism, if the optical layer does not restore all affected services. A simulation-based analysis shows the benefits of the proposed two-layer recovery scheme over single-layer recovery schemes. We demonstrate the advantages of finer granularity in IP layer recovery and the effectiveness in speed on the optical layer. The impact of several network parameters on recovery performance is also studied in the paper.     

IP over WDM网络的多层联合恢复策略

由于WDM网络承载着巨大的业务量,其网络可靠性日趋重要.在光层提供生存能力一向具有重要意义,然而由于光层聚集光路径及其粒度较粗的特征,也产生了许多的问题和挑战.MPLS及其扩展MP S的出现,为发展能够协调IP层和光层的联合保护/恢复策略提供了新的方法.鉴于此,文章首先简单介绍了现有MPLS/MP S的恢复机制,然后针对IP over WDM光网络提出了一种联合的二层恢复策略.在这种策略中,光层首先执行恢复动作,如果光层无法恢复所有受损的业务,则上层的IP层接着发起其自身的恢复机制.基于仿真的分析表明,所提出的二层联合恢复策略优于单层的恢复策略;若IP层恢复时具有更好的粒度优势,光层恢复时则具有更高的速度.     

The performance of TCP/IP for networks with high bandwidth-delayproducts and random loss

This paper examines the performance of TCP/IP, the Internet data transport protocol, over wide-area networks (WANs) in which data traffic could coexist with real-time traffic such as voice and video. Specifically, we attempt to develop a basic understanding, using analysis and simulation, of the properties of TCP/IP in a regime where: (1) the bandwidth-delay product of the network is high compared to the buffering in the network and (2) packets may incur random loss (e.g., due to transient congestion caused by fluctuations in real-time traffic, or wireless links in the path of the connection). The following key results are obtained. First, random loss leads to significant throughput deterioration when the product of the loss probability and the square of the bandwidth-delay product is larger than one. Second, for multiple connections sharing a bottleneck link, TCP is grossly unfair toward connections with higher round-trip delays. This means that a simple first in first out (FIFO) queueing discipline might not suffice for data traffic in WANs. Finally, while the Reno version of TCP produces less bursty traffic than the original Tahoe version, it is less robust than the latter when successive losses are closely spaced. We conclude by indicating modifications that may be required both at the transport and network layers to provide good end-to-end performance over high-speed WANs     

Packet concatenation at the IP level for performance enhancement in wireless local area networks

Wireless local area networks experience performance degradation in presence of small packets. The main reason for that is the large overhead added at the physical and link layers. This paper proposes a concatenation algorithm which groups IP layer packets prior to transmission, called PAC-IP. As a result, the overhead added at the physical and the link layers is shared among the grouped packets. Along with performance improvement, PAC-IP enables packet-based fairness in medium access as well as includes QoS support module handling delay-sensitive traffic demands. The performance of the proposed algorithm is evaluated through both simulations and an experimental WLAN testbed environment covering the single-hop and the widespread infrastructure network scenarios. Obtained results underline significant performance enhancement in different operating scenarios and channel conditions. Dzmitry Kliazovich received his Masters degree in Telecommunication science from Belarusian State University of Informatics and Radioelectronics in 2002. He is currently working towards the Ph.D. degree in University of Trento, Italy. From September 2005 to February 2006 he was a visiting researcher at the Computer Science Department of the University of California at Los Angeles. He is an author of more than 20 research papers published in international books, journals and conference proceedings. His main research interest lies in field of wireless networking with a focus on performance optimization and cross-layer design. Fabrizio Granelli was born in Genoa in 1972. He received the “Laurea” (M.Sc.) degree in Electronic Engineering from the University of Genoa, Italy, in 1997, with a thesis on video coding, awarded with the TELECOM Italy prize, and the Ph.D. in Telecommunications from the same university, in 2001. Since 2000 he is carrying on his teaching activity as Assistant Professor in Telecommunications at the Dept. of Information and Communication Technology—University of Trento (Italy). In August 2004, he was visiting professor at the State University of Campinas (Brasil). He is author or co-author of more than 60 papers published in international journals, books and conferences, and he is member of the Technical Committee of the International Conference on Communications (from 2003 to 2007) and Global Telecommunications Conference (GLOBECOM2003 and GLOBECOM2004). Dr. Granelli is guest-editor of ACM Journal on Mobile Networks and Applications, special issues on “WLAN Optimization at the MAC and Network Levels” and “Ultra-Wide Band for Sensor Networks”, and Co-Chair of 10th IEEE Workshop on Computer-Aided Modeling, Analysis, and Design of Communication Links and Networks (CAMAD’04). Dr. Granelli is General Vice-Chair of the First International Conference on Wireless Internet (WICON’05) and General Chair of the 11th IEEE Workshop on Computer-Aided Modeling, Analysis, and Design of Communication Links and Networks (CAMAD’06). His main research activities are in the field of networking and signal processing, with particular reference to network performance modeling, medium access control, wireless networks, cognitive radio systems, and video transmission over packet networks. He is Senior Member of IEEE and Associate Editor of IEEE Communications Letters.     

A novel layer 3 based movement detection algorithm for improving the performance of mobile IP

Mobile IP (MIP) provides efficient mobility support to applications at transport layer or above. MIP can provide better quality of service (QoS) in heterogeneous environment if it relies on layer 3 based movement detection techniques. Among the existing movement detection algorithms (MDAs), enhanced lazy cell switching (ELCS) provides better performance compared to eager cell switching (ErCS) and early cell switching (EyCS) by reducing movement detection delay when the mobile node (MN) crosses the overlapping cells. On the other hand, movement detection delay incurred by ErCS is always low compared to ELCS while the MN crosses adjacent cells. Thus, in this paper we propose a new MDA by retaining the positive features of ErCS and ELCS to provide better QoS in a network that comprises overlapping cells and adjacent cells. Our proposed MDA reduces the usage of radio resources of the MN and foreign agent (FA) in overlapping zone compared to ELCS. The simulation results on NS-2 demonstrates that our proposed MDA improves the performance of MIP as compared to other MDAs in terms of number of TCP data packets received by the MN, TCP throughput and amount of data transferred during simulation while MN crosses the overlapping area of two cells as well as when it roams in a network consisting of both types of cells overlapping and adjacent.     

多重信号广义似然接收机的设计及性能分析

提出并设计了一类通用的多重信号广义似然接收机.设计时只要求各重信号中高斯噪声是独立和零均值的,而允许是有色的或者非平稳的.推导结果表明,针对各重未知信号的最好情况(高信噪比,且各重信号幅度相等)、最不利情况(信噪比很低,且各重信号幅度独立)和适中情况(信噪比不太高也不太低,且各重信号幅度独立),所设计的接收机结构都是一致的,只是某些具体参数和模块不同. 本文还针对此接收机给出了性能分析的一个比较通用的方法.仿真结果与推导的理论性能相当吻合.     

多业务量矩阵下流量工程算法性能研究

传统域内流量工程TE(traffic engineering)算法中,基于OSPF/IS-IS的TE思想是通过调整链路权重使得全网的负载最均衡.由于Internet的急速发展以及用户业务需求的动态性导致业务量矩阵的不确定性,多业务量下的TE算法研究显得很有必要,而对于多业务量矩阵采取这种算法来最优化网络的研究很少见.本文提出了一种新的启发式基于OSPF/IS-IS链路权重调整的TE算法来解决多业务量矩阵,通过大量仿真实验分析了影响该算法性能的因子,从而为网络规划提供了很好的参考价值.     

Using multiple per egress burstifiers for enhanced TCP performance in OBS networks

Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of the number of burstifiers on TCP performance for an OBS network. The goodput of TCP flows between an ingress node and an egress node traveling through an optical network is studied as the number of assembly buffers per destination varies. First, the burst-length independent losses resulting from the contention in the core OBS network using a non-void-filling burst scheduling algorithm, e.g., Horizon, are studied. Then, burst-length dependent losses arising as a result of void-filling scheduling algorithms, e.g., LAUC-VF, are studied for two different TCP flow models: FTP-type long-lived flows and variable size short-lived flows. Simulation results show that for both types of scheduling algorithms, both types of TCP flow models, and different TCP versions (Reno, Newreno and Sack), TCP goodput increases as the number of burst assemblers per egress node is increased for an OBS network employing timer-based assembly algorithm. The improvement from one burstifier to moderate number of burst assemblers is significant (15–50% depending on the burst loss probability, per-hop processing delay, and the TCP version), but the goodput difference between moderate number of buffers and per-flow aggregation is relatively small, implying that an OBS edge switch should use moderate number of assembly buffers per destination for enhanced TCP performance without substantially increasing the hardware complexity.

Signal dependent degradation in noise performance of optimumdetectors for multiple signal detection

The detection of multiple signals in the presence of additive noise is addressed, and finite impulse response (FIR) filters are treated as arrays (or vectors) to facilitate mathematical manipulations. The problem is to find the filter coefficients such that the output is (i) indicative of the class of the input image, (ii) tolerant to additive input noise, and (iii) invariant to image distortions. The filter synthesis procedure is reviewed. Degradation in processor performance and the rise in output variance as the number of signals to be detected increases are discussed. It is shown that the variance is a nondecreasing function of the number of signals. Recursive expressions for the exact output variance and incremental changes in variance are derived     

Improved performance of bayesian solutions for inverse electrocardiography using multiple information sources

The usual goal in inverse electrocardiography (ECG) is to reconstruct cardiac electrical sources from body surface potentials and a mathematical model that relates the sources to the measurements. Due to attenuation and smoothing that occurs in the thorax, the inverse ECG problem is ill-posed and imposition of a priori constraints is needed to combat this ill-posedness. When the problem is posed in terms of reconstructing heart surface potentials, solutions have not yet achieved clinical utility; limitations include the limited availability of good a priori information about the solution and the lack of a "good" error metric. We describe an approach that combines body surface measurements and standard forward models with two additional information sources: statistical prior information about epicardial potential distributions and sparse simultaneous measurements of epicardial potentials made with multielectrode coronary venous catheters. We employ a Bayesian methodology which offers a general way to incorporate these information sources and additionally provides statistical performance analysis tools. In a simulation study, we first compare solutions using one or more of these information sources. Then, we study the effects of varying the number of sparse epicardial potential measurements on reconstruction accuracy. To evaluate accuracy, we used the Bayesian error covariance as well as traditional error metrics such as relative error. Our results show that including even sparsely sampled information from coronary venous catheters can substantially improve the reconstruction of epicardial potential distributions and that a Bayesian framework provides a feasible approach to using this information. Moreover, computing the Bayesian error standard deviations offers a means to indicate confidence in the results even in the absence of validation data.     

Exact deconvolution for multiple convolution operators-an overview,plus performance characterizations for imaging sensors

An updated review of the subject, including physically realizable examples along with explicit inverses and a computer simulation of the resulting large bandwidth, is given. A discussion of the ill-posedness of a single convolution operator clarifies the necessity of multiple operators. A precisely stated necessary and sufficient condition for inevitability is given. The performance of simultaneous convolution operators when there are sources of additive noise prior to the inverse is addressed. The main point is that for noise typical of electrooptical sensors, invertible multiple operators with their inverses will always outperform any set of single or multiple operators with the inverse omitted. A tutorial on the theory of distributions of compact support, which is used freely throughout the paper, is given in the appendix     

Analysis and simulation methods for performance evaluation of a multiple networked embedded architecture

This paper deals with the modeling and the validation of multiple networked embedded computer systems supporting in-vehicle applications. In this context, the authors developed a modular modeling and simulation technique. This approach allowed the development of reusable component models with clearly defined interfaces. The building of a whole application model is then obtained by the integration of these components, so that model construction and result analysis are made easy. In fact, thanks to the formal definition of components, interfaces, and composition rules, this step is automatically achieved. In the context of the CAROSSE project, we implemented this methodology in the Carosse-Perf tool. Herein, the authors detail the methodology together with its modeling principles and the resulting definition of basic components and interfaces. Finally, they apply it to a case study drawn from a PSA Peugeot-Citroen application.     

光码分多址系统中二维QCC码的误码性能分析

对基于一维二次同余码构成的QCC/QCC跳频扩时码和QCC/OOC跳频扩时码进行了详细的码字性能分析.通过计算不同情况下码字的碰撞次数,得出了互相关均值,并对这两种二维QCC码进行了误码率的仿真比较和理论分析,数值模拟表明,当码字长度确定时,QCC/OOC码的码字性能较QCC/QCC码更加优良,码字容量更大,但对跳频码片的要求较高.当码字容量确定时,较大p值的QCC/QCC码的码字性能更加优良,但码字长度相对较长.     

On the performance evaluation, selection, and design ofunique-words for time-division multiple access systems

The issues of performance evaluation, selection, and design of unique-words for time-division multiple-access systems are addressed for both additive white Gaussian noise and time-varying multipath fading channels. An efficient algorithm is proposed to compute the probability of a missed detection, which serves as the performance index of unique-words. Also, a simple upper bound on the probability of a missed detection is derived. This bound has been shown very tight for a large range of bit error rate. Based on this tight upper bound, a two-step algorithm is proposed for easy selection and design of good unique-words. For time-varying multipath fading channels, the performance of unique-words is evaluated for Rayleigh and Rician fading characteristics, which are suitable models for mobile and personal communication environments. The results show that the degradation caused by the fading effect can be larger than 10 dB for the performance of practical interest