路由器别名解析程度影响分析

路由器别名解析是基于traceroute机制的因特网路由器级拓扑测量中的难点和重要环节之一,生成的路由器级拓扑图的结构特征与别名解析完全性密切相关。以具有幂律分布的拓扑图为基础拓扑图,采用最短路径方式进行模拟测量。实验结果表明了别名解析不完全可能使测量得到的拓扑图与基础拓扑图的结构特征不一致。更为重要的是,对于大规模路由器级拓扑测量,随着测量源点数量的增加,需同时提高别名解析完全性,才能使测量得到的拓扑图更接近于实际的拓扑图。     

Netpiler: detection of ineffective router configurations

Configuring a network is a tedious and error-prone task. In particular, configuring routing policies for a network is complex as it involves subtle dependencies in multiple routers across the network. Misconfigurations are common and certain misconfigurations can bring the Internet down. In 2005, a misconfigured router in AS 9121 blackholed traffic for tens of thousands of networks in the Internet. This paper describes NetPiler, a system that detects router misconfigurations. NetPiler consists of a routing policy configuration model and a misconfiguration detection algorithm. The model is applicable to routing policies configured on a single router as well as to network-wide configuration. Using the model, NetPiler detects configuration commands that do not influence the behavior of the network - we call these configurations ineffective commands. Although the ineffective commands could be benign, sometimes when the commands are mistakenly configured to be ineffective, they cause the network to misbehave deviating from the intended behavior. We have implemented NetPiler in approximately 128,000 lines of C++ code, and evaluated it on the configurations of four production networks. NetPiler discovers nearly a hundred ineffective commands. Some of these misconfigurations can result in loss of connectivity, access to protected networks, and financial implications by providing free transit services. We believe NetPiler can help networks to significantly reduce misconfigurations.     

Conflict multiplicity estimation and batch resolution algorithms

The standard model of a multiple-access channel with ternary feedback is considered. When packets of a batch of k nodes initially collide, it is assumed that no a priori statistical information about k is available. An algorithm is presented and analyzed that enables the nodes to compute a statistical estimate of k. Combining the estimation procedure with tree algorithms leads to batch-resolution algorithms that resolve conflicts more efficiently than any other reported to date. Both complete-resolution and partial-resolution algorithms are presented     

Network reachability‐based IP prefix hijacking detection

IP prefix hijacking is a major threat to the security of the Internet routing system owing to the lack of authoritative prefix ownership information. Despite many efforts to design IP prefix hijack detection schemes, no existing design satisfies all the critical requirements of a truly effective system, i.e. to be real‐time, deployable, and robust. In this paper, we present a novel approach that detects IP prefix hijacking in the current Internet environment. The focus of this work is on maintaining the Border Gateway Protocol routing infrastructure and not relying on mutual cooperation to ensure ease of deployment. In addition, we look at fingerprinting two autonomous systems that have the same IP prefix to distinguish hijacking events from legitimate routing updates. This paper proposes a practical and deployable IP prefix hijacking detection algorithm with live hosts on the Internet. Copyright © 2012 John Wiley & Sons, Ltd.     

CP-CDMA系统中的时频差分编码与检测

提出了一种新的用于基于循环前缀的直接序列扩频码分多址（CP-CDMA）系统的差分编码与检测方法。该方法利用信道在时域与频域上的相关性进行时频两维差分编码,在接收端采用基于最小均方误差准则的非相干检测。计算机仿真结果显示,该方法与现有差分编码方法相比,在快速时变多径信道中具有更优的比特误码率性能和更稳健的抗多普勒频移特性。     

High resolution two-dimensional ARMA spectral estimation

The authors present a practical algorithm for estimating the power spectrum of a 2-D homogeneous random field based on 2-D autoregressive moving average (ARMA) modeling. This algorithm is a two-step approach: first, the AR parameters are estimated by solving a version of the 2-D modified Yule-Walker equation, for which some existing efficient algorithms are available; then the MA spectrum parameters are obtained by simple computations. The potential capability and the high-resolution performance of the algorithm are demonstrated by using some numerical examples     

基于遗传算法的机场场面目标冲突解脱方法

为了解决机场场面运行研究中场面目标冲突解脱的问题,提出一种基于遗传算法的混合整数规划模型,详细研究了等待时间权重系数对冲突解脱的影响,对满足等待时间约束的情况,进行滑行时刻优化;不满足等待时间约束时,将典型冲突避免、滑行规则及安全间隔作为约束条件,建立场面滑行调度优化模型,基于遗传算法给出了飞机冲突路径的解脱优化算法.仿真结果表明这方法既可提高场面目标冲突解脱效率,又能得到滑行最优路径,验证了模型的可行性.     

Demonstration of an optical-label switching router with multicast and contention resolution at mixed data rates

This letter experimentally demonstrates a scalable optical-label switching router architecture that supports a limited multicast function. A semiconductor-optical-amplifier-based Mach-Zehnder interferometer wavelength converter performs multiwavelength conversion for multicast at 10 Gb/s by cross-phase modulation. With a 2.5-Gb/s unicast channel, the experiment also demonstrates contention resolution in the wavelength domain at mixed data rates.     

Optimal edge detection in two-dimensional images

This paper presents a new edge detection scheme that detects two-dimensional (2-D) edges by a curve-segment-based detection functional guided by the zero-crossing contours of the Laplacian-of-Gaussian (LOG) to approach the true edge locations. The detection functional is shown to be optimal in terms of signal-to-noise ratio (SNR) and edge localization accuracy; it also preserves the nice scaling property held uniquely by the LOG in scale space.     

Issues and trends in router design

Future routers must not only forward packets at high speeds, but also deal with nontrivial issues such as scheduling support for differential services, heterogeneous link technologies, and backward compatibility with a wide range of packet formats and routing protocols. The authors outline the design issues facing the next generation of backbone, enterprise, and access routers. The authors also present a survey of advances in router design, identifying important trends, concluding with a selection of open issues     

High resolution two-dimensional minimum free energy AR spectral estimation

We extend the minimum free energy (MFE) parameter estimation method to 2-D fields. This 2-D MFE method may be used to determine autoregressive (AR) model parameters for spectral estimation of 2-D fields. It may also be used to provide AR models for texture synthesis. The performance of the technique for closely spaced sinusoids in white noise is demonstrated by numerical example. Better results can be achieved than with the multidimensional Levinson algorithm.     

The detection and resolution of optical signals

The principles of statistical signal-detection theory are applied to the detection of optical signals by postulating the photoelectric effect as the mechanism for the interaction of the electromagnetic field of the light with matter. The data with which the detection system works are the numbers of photoelectric events in various parts of a receptor on which the light falls after passing through an aperture. The theory prescribes how the data should be processed and measures the detectability of the signals in terms of an SNR. The theory is applied to the detection of a point source and of an array of incoherent point sources, all against a uniform background. The resolution of two weak close point sources of radiation observed against a uniform background is also treated as a problem in the testing of hypotheses, and the reliability of the system derived on this basis is measured by an SNR that is a function of the angular separation of the sources. The estimation of the parameters of an optical signal is discussed from the standpoint of statistical estimation theory. Estimation of the angular position of a point source against a uniform background is treated as an example.     

Doppler dispersion effects in matched filter detection and resolution

Conventional matched filters which use pseudorandom or noise-like waveforms attempt to compensate for the Doppler effect by cross-correlating the received waveforms with frequency shifted replicas of the transmitted waveform. However, frequency translation is only an approximation to the actual Doppler effect which is a time-expansion or time-compression of the waveform resulting from the continuous expansion or compression of the transit path. This paper investigates the effects of Doppler dispersion in matched filters which use frequency translation for Doppler compensation. It is found that the effects of Doppler dispersion are independent of the carrier frequency and negligible if the dispersion product, i.e., the absolute magnitude of the product of the signal bandwidth, duration, and delay rate, is less than unity. If the dispersion product is greater than unity the dispersion effects are serious. In the latter case the time and frequency resolution of the system are degraded and the output pulse is reduced in amplitude. The maximum improvement that can be obtained in the signal-to-noise power ratio is equal to the reciprocal of the delay rate magnitude. This maximum signal-to-noise gain is achieved when the time-bandwidth product of the receiver is chosen such that the dispersion product is approximately unity.     

OBS基于回退和信道分级的冲突解决算法

解决突发包的冲突问题是光突发交换网络的关键技术之一。为了降低突发包冲突时丢包率,提出了一种新型的基于信道分级和回退机制的冲突解决算法,该算法考虑突发业务优先级,将信道分成两个级别,有区别地对待高低优先级两种业务类型,并且增加了一部分回退信道作为保护和重发冲突数据包,能够有效地保证高优先级业务的传输可靠性。结果表明,当冲突发生时,网络能根据此时高低优先级业务量的比重配比,自适应地调节两个级别信道的数量,兼顾到低优先级业务的低丢包率,保证了较低的延时率。此算法相比以往的冲突解决算法具有较低的丢包率和相对小的延时率。     

未来光网络中的交换路由器

IP业务的爆炸式增长与DWDM技术的突飞猛进为新的WDM网络直接承载IP业务创造了条件。光交换和交换路由器的发展提供一种集成了智能IP路由技术和大容量光交换网络的交换路由器模型。这种交换路由器支持高QoS保证 ,简化了光核心网络结构 ,是近期光联网的理想解决方案     

Broad-band detection based on two-dimensional mixed autoregressivemodels

Two detectors for broadband plane waves in colored noise fields that use a linear array are described. The signal spectrum, arrival angle, and noise field coloration are not known a priori. Using a two-dimensional mixed autoregressive model, a generalized-likelihood-ratio test and its weak-signal equivalent, the Rao test, are derived. The performances of the proposed detectors are shown by computer simulations to be superior to those of conventional Fourier-based methods. Detection results for real data are presented     

An evaluation of a two-dimensional array detector for high resolution PET

A two-dimensional array detector system, consisting of 4x8 matrices of bismuth germanate (BGO) crystals coupled to four photomultipliers, was evaluated. Coincidence timing resolution of a pair of array detectors was 6.1 ns FWHM and 11.3 ns FWTM. Energy resolution per individual crystal ranged from 16.8 to 24.1% FWHM at 511 keV for an amplitude variation of a factor of 2.8. The signals from the photomultipliers were summed pairwise, the pairs in each dimension subtracted, and the differences divided by the amplitude of the signal summed from all four photomultipliers. The resulting two-pulse-height spectra contained peaks corresponding to the row or column containing the detector of interaction. Six conditions of detector identification were tested. The correct identification of detector ranged from 76% to 87% of the events. The largest single factor in improving crystal identification and spatial resolution was energy discrimination.     

High resolution parametric modelling for two-dimensional radar target using prony algorithm

On the conditions of low-resolution radar, a parametric model for two-dimensional radar target is described here according to the theory of electromagnetic scattering and the geometrical theory of diffraction. A high resolution estimation algorithm to extract the model parameters is also developed by building the relation of the scattering model and Prony model. The analysis of Cramer-Rao bound and simulation show that the method here has better statistical performance. The simulated analysis also indicates that the accurate extraction of the diffraction coefficient of scattering center is restricted by signal to noise ratio, radar center frequency and radar bandwidth.     

Resource management in software-programmable router operatingsystems

Future routers will not only forward data packets but also provide value-added services, such as security, accounting, caching, and resource management. These services ran be implemented as general programs, to be invoked by traversing packets embedding router program calls. Software-programmable routers pose new challenges in the design of router operating systems (OS). First, router programs will require access to diverse system resources. The resource demands of a large community of heterogeneous resource consumers must either be coordinated to enable cooperation or arbitrated to resolve competition. Second, it is beneficial to concurrently support multiple virtual machines, each with a guaranteed share of physical resources. This allows services to be customized and to seamlessly evolve. We present the design and implementation of a next generation router OS that can meet the above challenges. We define an orthogonal kernel abstraction of resource allocation, which can schedule various time-shared and space-shared resources with quality of service (QoS) differentiation and guarantees. A scalable and flexible packet classifier enables dynamic resource binding and per-flow processing of received packets. We have prototyped our system on a network of UltraSPARC and Pentium II computers. Currently, QoS-aware schedulers for CPU time, forwarding bandwidth, memory-store capacity, and capacity for secondary data stores have been integrated. We present experimental results on various aspects of resource management in our system     

未来光网络中的交换路由器

IP业务的爆炸式增长与DWDM技术的突飞猛进为新的WDM网络直接承载IP业务创造了条件,光交换和交换路由器的发展提供一种集成了智能IP路由技术和大容量光交换网络的交换路由器模型。这种交换路由器支持高QoS保证,简化了光核心网络结构,是近期光联网的理想解决方案。