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     

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     

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     

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.     

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.     

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     

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     

EEG-based lapse detection with high temporal resolution

A warning system capable of reliably detecting lapses in responsiveness (lapses) has the potential to prevent many fatal accidents. We have developed a system capable of detecting lapses in real-time with second-scale temporal resolution. Data was from 15 subjects performing a visuomotor tracking task for two 1-hour sessions with concurrent electroencephalogram (EEG) and facial video recordings. The detector uses a neural network with normalized EEG log-power spectrum inputs from two bipolar EEG derivations, though we also considered a multichannel detector. Lapses, identified using a combination of video rating and tracking behavior, were used to train our detector. We compared detectors employing tapped delay-line linear perceptron, tapped delay-line multilayer perceptron (TDL-MLP), and long short-term memory (LSTM) recurrent neural networks operating continuously at 1 Hz. Using estimates of EEG log-power spectra from up to 4 s prior to a lapse improved detection compared with only using the most recent estimate. We report the first application of a LSTM to an EEG analysis problem. LSTM performance was equivalent to the best TDL-MLP network but did not require an input buffer. Overall performance was satisfactory with area under the curve from receiver operating characteristic analysis of 0.84 +/- 0.02 (mean +/- SE) and area under the precision-recall curve of 0.41 +/- 0.08.     

Haze detection and removal in high resolution satellite image withwavelet analysis

A procedure for haze detection and removal from high-resolution satellite images using wavelet analysis (HAWAT) has been developed. It involves the analysis of the low spatial frequency information content of a scene. The image contaminated by haze is decomposed into different spatial layers with wavelet transforms. Although haze is distributed in the lower frequency layer, this layer may also contain a component of land cover that is spatially and temporally relatively stable. A haze-free reference image of the same area is used to characterize land cover. The component of the characterized land cover is then subtracted with wavelet analysis. The residual wavelet coefficients are used to construct a spatially varying mask for subsequent haze detection and removal. After smoothing, the mask is subtracted from the contaminated image to obtain a corrected image with haze-off characteristics. Both visual inspection and statistical accuracy assessment show that the haze calibration is valid and robust     

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。     

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.     

Adaptive channel estimation using cyclic prefix in multicarriermodulation system

Multicarrier modulation (MCM) is a promising technique for high rate data transmission and the channel estimation is very important for the implementation of MCM. We found that the cyclic prefix, originally used solely to reduce the intersymbol interference (ISI), can be viewed as a source of channel information. Based on this observation, we propose an adaptive channel estimation algorithm using the cyclic prefix. This algorithm can adaptively track the channel variation without additional training sequences     

Cisco路由安全性分析和改进

路由器安全在网络安全领域占有非常重要的地位,针对互联网中使用最为广泛的Cisco路由器,从3个方面出发分别说明了Cisco路由器所面临的各种危险,从原理的角度阐述了由于Cisco路由器自身操作系统IOS的缺陷所导致的一些常见漏洞和随之带来的安全问题.介绍了路由器所使用的SNMP协议带来的安全隐患,并提供了详尽案例来分析网络上常见的攻击路由器的所使用的工具和方法.最后针对这些攻击手段和各种漏洞提出了关于网络安全建设和路由器使用上的一些建议.     

Some detection and resolution properties of maximum entropy spectrum analysis

An experimental comparison between conventional spectral estimation techniques and a Maximum Entropy Spectral Analysis (MESA) algorithm is made. Three factors in the experimentation make the results of considerable interest to workers in acoustic signal processing, especially sonar and surveillance. These are the range of signal-to-noise ratio (SNR) studied, the comparisons based equal length observation intervals and the use of ensemble averaging after maximum entropy analysis. Results are presented, for both resolution and peak signal response, which tend to indicate that the Maximum Entropy Method (MEM) offers considerable promise in achieving the detection performance of long observation interval discrete Fourier transform (DFT) analysis at a much reduced length of observation time.     

Object detection using high resolution near-field array processing

The authors present an algorithm for the detection and localization of an unknown number of objects buried in a halfspace and present in the near field of a linear receiver array. To overcome the nonplanar nature of the wavefield over the array, the full array is divided into a collection of subarrays such that the scattered fields from objects are locally planar at each subarray. Using the multiple signal classification (MUSIC) algorithm, directions of arrival (DOA) of locally planar waves at each subarray are found. By triangulating these DOAs, a set of crossings, condensed around expected object locations, are obtained. To process this spatial crossing pattern, the authors develop a statistical model for the distribution of these crossings and employ hypotheses testing techniques to identify a collection of small windows likely to contain targets. Finally, the results of the hypothesis tests are used to estimate the number and locations of the targets. Using simulated data, they demonstrate the usefulness and performance of this approach for typical background electrical properties and signal to noise ratios     

GMPLS-based photonic multilayer router (Hikari router)architecture: an overview of traffic engineering and signalingtechnology

A new extended signaling and traffic engineering method for the GMPLS-based photonic and electrical multilayer router (Hikari router) is proposed. The method allows dynamic optical network management and photonic signal recovery, such as regeneration, reshaping, etc., to be realized adaptively. Wavelength conversion is also adaptive, which reduces network cost. Multilayer traffic engineering, which yields the dynamic cooperation of IP and photonic layers, is described to provide IP services cost effectively. To realize multilayer traffic engineering, we propose the OSPF extension, which advertises both the number of total wavelengths and the number of unused wavelengths, and the RSVP-TE extension, which minimizes the number of wavelength conversions needed. In addition, this paper proposes a heuristics-based multilayer topology design scheme that uses IP traffic measurements in a generalized multi-protocol label switch (GMPLS). The proposed scheme yields the optical label switch path (OLSP) network topology, that is, OLSP placement, that minimizes network cost, in response to fluctuations in IP traffic demand. In other words, the OLSP network topology is dynamically reconfigured to match IP traffic demand. Networks are reconfigured by the proposed scheme so as to utilize network resources in the most cost effective manner