Feasibility of IP restoration in a tier 1 backbone

Large IP networks usually combine protection and restoration mechanisms at various layers of the protocol stack to minimize service disruption in the event of failures. Sprint has chosen an IP-based restoration approach for building a highly available tier 1 IP backbone. This article describes the design principles of Sprint's network that makes IP-based restoration an effective and cost-efficient approach. The effectiveness of IP-based restoration is evaluated by analyzing network failure characteristics, and measuring disruptions in service availability during controlled failure experiments in the backbone. Current trends for improving the performance of IP-based restoration are also discussed.     

Packet-level traffic measurements from the Sprint IP backbone

Network traffic measurements provide essential data for networking research and network management. In this article we describe a passive monitoring system designed to capture GPS synchronized packet-level traffic measurements on OC-3, OC-12, and OC-48 links. Our system is deployed in four POP in the Sprint IP backbone. Measurement data is stored on a 10 Tbyte storage area network and analyzed on a computing cluster. We present a set of results to both demonstrate the strength of the system and identify recent changes in Internet traffic characteristics. The results include traffic workload, analyses of TCP flow round-trip times, out-of-sequence packet rates, and packet delay. We also show that some links no longer carry Web traffic as their dominant component to the benefit of file sharing and media streaming. On most links we monitored, TCP flows exhibit low out-of-sequence packet rates, and backbone delays are dominated by the speed of light.     

基于CERNET主干信道的IP流数据Trace

主干互联网的IP流数据对研究互联网具有重大价值,但实际公布的这类数据量很少,尤其是没有经过抽样处理的原始数据,原因主要在于主干信道采集难度大和IP地址隐私等方面.以CERNET一个省网边界(1G×3)采集的1个小时的连续的IP报头为原始数据,依据相应的省网IP地址构成的特点与实际需求,对IP地址前缀保留匿名化算法Crypto-PAn进行了改进,在提高实现效率的基础上保留了地址类型,用改进后的算法将上述原始数据进行了相应的处理,并将结果在互联网上公布,供有关研究下载.     

环形IP骨干网

环形网具有很高的生存能力及良好的业务疏导和自愈能力,因此,环形拓扑在传送网中得到了广泛的应用。目前,大多数已建成的SONET传送网或WDM传送网都采用了物理上的环形网结构。尽管本质上环形网由节点间的点到点传输线路组成,但传送网基础设施（包括终端复用器、ADM、DXC等）及光缆线路组成的传输系统平台在电路的调配上却具有相当的灵活性。通过SONET强大的OAM功能,环上节点可在各种子速率下配置成具有不同业务功能的逻辑拓扑结构,如星形、环形、格形等。SONET这种基于同步复接技术的电路调配方式在最初的IP网络规划中也…     

IP over DWDM宽带IP主干网

随着Internet(因特网)主机数的增长以及宽带业务带来的主机业务流量的增加，互联网上业务量以指数形式增加。作为一种最有前途的解决用户需求不断增加的方案。IP overDWDM(基于密集波分复用的互联网协议)受到业界的广泛关注。为此主要讨论了IPoverDWDM技术，包括其原理、关键器件、路由选择以及发展趋势。     

Optical burst switching: a viable solution for terabit IP backbone

Wavelength-division multiplexing has emerged as an important physical layer technology. Optical transmission provides a physical layer capable of carrying bits at the speed at the order of a gigabit per second. Optical burst switching is proposed to overcome the shortcomings of conventional WDM deployment, such as lack of fine bandwidth granularity in wavelength routing and electronic speed bottlenecks in SONET/SDH. We describe an architecture for IP network over the OBS WDM transmission core. The use of MPLS-type technique for forwarding data bursts and the inclusion of a medium access control layer between the optical (WDM) and IP layers are the key ingredients of the proposed architecture. In particular, the architecture is based on provisioning MPLS paths, also called label switched paths, of desired quality of service through the OBS WDM transmission core. The MAC layer performs various OBS-specific functions, such as burst assembly, burst scheduling, and offset setting/traffic shaping. While burst assembly and burst scheduling are relatively straightforward, we point out that the offset setting strategy has significant impact on the performance of IP network operating over OBS WDM core. We describe a shaping scheme to set the offset, an important system parameter for OBS, between the successive data bursts of a given data stream (label switched path) and their associated control packets. This scheme results in robust operation of the network and also facilitates traffic engineering. Guidelines are provided for implementing various IP QoS mechanisms in the optical backbone using OBS.     

Measurement and analysis of single-hop delay on an IP backbone network

We measure and analyze the single-hop packet delay through operational routers in the Sprint Internet protocol (IP) backbone network. After presenting our delay measurements through a single router for OC-3 and OC-12 link speeds, we propose a methodology to identify the factors contributing to single-hop delay. In addition to packet processing, transmission, and queueing delay at the output link, we observe the presence of very large delays that cannot be explained within the context of a first-in first-out output queue model. We isolate and analyze these outliers. Results indicate that there is very little queueing taking place in Sprint's backbone. As link speeds increase, transmission delay decreases and the dominant part of single-hop delay is packet processing time. We show that if a packet is received and transmitted on the same linecard, it experiences less than 20 /spl mu/s of delay. If the packet is transmitted across the switch fabric, its delay doubles in magnitude. We observe that processing due to IP options results in single-hop delays in the order of milliseconds. Milliseconds of delay may also be experienced by packets that do not carry IP options. We attribute those delays to router idiosyncratic behavior that affects less than 1% of the packets. Finally, we show that the queueing delay distribution is long-tailed and can be approximated with a Weibull distribution with the scale parameter a=0.5 and the shape parameter b=0.6 to 0.82.     

一个标准化模块化的IP数据广播集成方案

IP数据广播技术在这几年里取得了长足的进展,但在标准化和模块化方面的建设却不多。基于近两年新技术的发展和新需求的出现,介绍了一个标准化、开放化、模块化的IP数据广播集成方案的设计、模块划分及模块之间的标准接口。可以预料标准化、模块化的IP数据广播将促进应用的进一步发展,并产生质的变化,如卫星广播网格。     

A flow-based approach to modeling ADSL traffic on an IP backbone link

Measurements from an Internet backbone link carryingtcp traffic towards differentadsl areas are analyzed in this paper. For traffic analysis, we adopt a flow-based approach and the popular mice/elephants dichotomy. The originality of the experimental data reported in this paper, when compared with previous measurements from very high speed backbone links, is that commercial traffic comprises a significant part due to peer-to-peer applications. This kind of traffic exhibits some remarkable properties in terms of mice, elephants and bit rates, which are thoroughly described in this paper. Global traffic is actually decomposed into several flow components on the basis of the mice/elephants dichotomy. Mice due p2p protocols and mice due to classical Internet applications such ashttp, ftp, etc. are analyzed separately. It turns out that by adopting a suitable level of aggregation, global traffic can be described by means of usual tele-traffic models based on M/G/∞ queues with Weibullian service times. The blobal bit rate can then be approximated by the superposition of Gaussian processes perturbed by a white noise.     

Analysis and design of backbone architecture alternatives for IP optical networking

The unprecedented growth of IP traffic is leading Internet service providers and network operators worldwide to investigate architectural alternatives for cost effective, reliable, scalable, and flexible multiterabit IP backbones. In this paper, several overlay, service, and transport layer networking architectures, which employ IP, MPLS, SONET/SDH, and DWDM technologies, are proposed and analyzed. Multiple parameters, such as network capacity, cost, restoration strategy, reconfigurability, and accommodation of preemptable traffic, are considered for the architectural comparison. Detailed network design and economic analysis are provided for the different alternatives considering a typical nationwide U.S. backbone with projected IP traffic in approximately three years. Several sensitivity analysis results are also shown, to evaluate the effect of cost changes in some of the critical technological factors in these architectures, such as 10 Gb/s optics cost or IP router cost. The results show the value of transport layer networking architectures for multiterabit IP backbones, and how, when compared to service layer architectures, they provide additional desirable features such as wavelength reconfigurability and restoration scalability.     

光交换、路由器与P比特级IP网

为了适应广域网（ＷＡＮ）对带宽需求的高速增长,必须以格形全光广域核心网取代现有的同步光环网（ＳＯＮＥＴ）。人们对在核心网络中采用波长交换技术给予了极大的关注,却忽略了光交换技术在核心网边缘的光分组路由器的重大作用。 当今路由器的端口数一般是每束光纤中光纤数目的数倍,这在目前是绰绰有余的,因为可以把每一束光纤当作一个目的地来处理。但是为了有效地利用波长交换,必须把每一个收到的分组搭在适当的波长上以便直接送到距最终目的地最近的节点,从而尽量减少中间路由。当每个路由节点的端口数与它所服务的波长数相当时…     

骨干出口路由策略及节点增容方案探讨

本文论述了骨干网应用的路由技术和策略，提出了北京节点增容方案，并从路由策略和网络架构的角度分析了几种方案的适应性。     

Microwave measurements with active systems

Possible practical applications of a novel technique for the measurement of dielectric constant, or analogous quantities, at microwave frequencies are considered. Although originally developed for microwave diagnostics in plasma-physics research, it is felt that the method may be of interest in certain problems of current scientific and technological interest. Conventional systems for the determination of microwave dielectric constant are "passive" in the sense that the quantities of interest are determined from a shift in phase, or frequency, in a passive element, such as a microwave bridge; the microwave energy required for the measurement is derived from an external source. In the method described here, use is made of an "active" system in which a positive feedback loop containing a microwave amplifier provides positive gain. The entire configuration, including the measurement element, then comprises a microwave oscillator, the frequency and amplitude of the oscillator containing information on the quantities being measured. It appears that the method can be attractive from the point of view of sensitivity, response time, linearity, dynamic range, and convenience of readout. In addition, an active system can function as its own telemetry unit. Aspects of the theoryof active systems are analyzed, and factors that enter into the design and construction of such systems are described. Experiments carried out to evaluate active systems in gas turbulence measurements and in the determination of size distributions of particles with dimensions of tens of microns are described.     

Noise measurements on distributed-feedback optical amplifiers usedas tunable active filters

Resonant, single-mode optical amplifiers that show promise for use as fast, tunable filters in multiwavelength communication networks are discussed. According to recent theoretical predictions, the photocurrent signal-to-noise ratio at the output of such a filter should exhibit a simple dependence on both the mean amplified-signal power and the mean amplified-spontaneous-emission power. This prediction is confirmed via direct measurement of the photocurrent signal-to-noise ratio at the output of a 1.5-μm distributed-feedback amplifier biased slightly below its lasing threshold     

基于SHA-1算法的IP核设计

本文在简要介绍安全hash算法SHA-1的基础上,给出了SHA-1算法IP核的整体 结构的设计方案格电路的工作原理。结合SHA-1算法的特点,重点介绍和设计了数据填充单元和 存储单元。用VHDL描述该电路结构,并且在FPGA上验证了该结构的正确性。     

基于SVM和CRF双层分类器的英文电子病历去隐私化

去隐私化是2014 i2b2/UTHealth中的一个任务,目的在于识别并移除电子病历中的隐私信息.本文提出了一种基于支持向量机(SVMs)和条件随机场(CRFs)双层分类模型的去隐私化方法,经过预处理将病历文本进行词切分(tokenize)处理,并在此基础上抽取4类特征,训练SVM模型对隐私信息实体边界进行划分并将结果作为特征添加到特征集中,通过CRF训练多分类器,并通过该分类器对各个类别的隐私信息进行识别.实验表明双层分类模型对于隐私信息识别是有效的,结果F值达到0.9110.     

Picosecond pulse measurements using the active laser medium

A simple method for measuring the pulse lengths of synchronously pumped dye lasers which does not require the use of an external nonlinear medium, such as a doubling crystal or two-photon fluorescence cell, to autocorrelate the pulses is discussed. The technique involves feeding the laser pulses back into the dye jet, thus correlating the output pulses with the intracavity pulses to obtain pulse length signatures in the resulting time-averaged laser power. Experimental measurements were performed using a rhodamine 6G dye laser pumped by a mode-locked frequency-doubled Nd:YAG laser. The results agree well with numerical computations, and the method proves effective in determining lengths of picosecond laser pulses     

Error-rate measurements on a 1 Gbit/s fibre-optic communications link

Error-rate measurements made on a 1 Gbit/s fibre-optic communications link are described. The link utilises a GaAlAs d.h. injection laser, a 1.6 km single-mode fibre, an avalanche photo-diode and a multiplexer and demultiplexer for four 250 Mbit/s channels. A comparison of the measured results with calculated data using a Gaussian approximation showed good agreement within 2 dB.