ATM上行口与以太网上行口的ADSL技术比较

ADSL局端设备为DSLAM，目前一般采用ATM STM-1接口或100M/1000M以太网接口连接到ATM或IP城域网上。对采用ATM上行口和采用以太网上行口的DSLAM进行比较和分析，希望能对选择和使用ADSL设备有所帮助。     

IP-DSLAM的应用组网策略

随着ADSL宽带接入技术的普及和发展,同时为了适应IP城域骨干网宽带接入的需要,ADSL局端设备DSLAM开始提供以太网上行接口,这类设备统称为“IPDSALM”。由于ADSL线路普遍采用了ATM传送模式,业已成熟并广泛应用的传统DSALM设备普遍采用了ATM交换机制并提供ATM上行接口。而IP DSLAM设备根据所采用的交换机制则可分为两类:一类为采用ATM交换机制,同时提供以太网上行接口,其主流的实现方式为仅提供ATM至以太网的链路层转换,但也有些设备在其上行以太网接口板卡上甚至实现了网络层的认证和路由的功能;而另一类则考虑到当前绝大多数实用的VDSL线路采用了以太网传送模式,而且面向公众宽带数据接入市场,存在着将ADSL与VDSL集成的需要,DSLAM设备采用了以太网交换机制,从而使ADSL线路中ATM信元至以太网帧的转换在线路板卡上实现;由于这类设备采用了以太网交换机制,因此也较容易实现网络层的认证和路由的功能。综上所述的种种实现方式,IPDSLAM设备又可根据其协议层次功能的实现分为二层(即链路层)IP DSLAM和三层(即网络层)IP DSLAM。     

ADSL DSLAM的技术演进

第一代：纯ATM结构第一代ADSL DSLAM从下行的线路到上行的接口全部采用ATM方式，这是最符合ADSL技术自身特点的结构。这一代的DSLAM只能使用ATM网络作为其接入与核心网络，而ATM网络接口直到目前为止仍然仅能提供622M接口，交换容量也通常只有几个GB，这样就导致在提供大容量的核心网络时要使用大量的ATM设备，再加上ATM设备本身成本较高，也就导致了ATM核心网络的建网成本高昂。第一代ADSL DSLAM建设成本高昂不仅仅来自ATM网络本身，还来自于网关设备。无论ATM网络建设的有多么丰富，最终还要与以IP技术为核心的In…     

XpressLink在重庆电信的应用

重庆电信ADSL网络建设的规模约为15万端口,其中约50％采用了西门子的DSLAM XpressLink。XpressLink全部应用在重庆主城区,既有ATM上连的DSLAM,也有IP上连的DSLAM。25000线ATM上连的ADSL共占用14个ATM STM-1接口,平均每个接口约接入1800端口ADSL,既可充分利用STM-1的带宽,也可保证用户接入带宽。而每1800端口ADSL的汇聚都是通过XpressLink的自身级联实现的。XpressLink在级联     

XpressLink在重庆电信的应用

西门子XpressLink全部应用在重庆主城区,其中上清寺区局和观音桥区局既有ATM上连的DSLAM,也有IP上连的DSLAM,杨家坪区局和沙坪坝区局应用的都是IP上连的DSLAM。图1,图2分别是上清寺区局和观音桥区局ATM上连DSLAM的网络拓扑图。在图中,25,000线ATM上连的ADSL共占用14个ATMSTM-1接口,平均每个接口接入大约1,800端口ADSL,既可以保证充分利     

利用XpressLink架构重庆电信ADSL网络

1重庆电信ADSL网络的架构重庆电信运营网络目前拥有大约150000个ADSL端口,其中约50%的DSLAM设备都是采用西门子的XpressLink,而且这些设备主要应用在重庆的主城区。ADSLDSLAM接入城域网时主要采用IP链路上连和ATM链路上连两种方式。在重庆的几大主城区中,上清寺区和观音桥区既采用了ATM链路上连方式,又采用了IP链路上连方式;杨家坪区和沙坪坝区都是采用IP链路上连方式。上清寺区和观音桥区采用ATM链路上连的DSLAM的网络拓扑分别如图1和图2所示。在这两个图中,25000线以ATM链路上连的ADSL共占用了14个ATMSTM-1接口,平…     

ADSL与Cable Modem技术比较

<正> 在从现有的窄带接入技术向最终光接入解决方案发展过程中,会有许多非常有生命力的过渡技术,其中,基于电话线的AD-SL技术和基于有线电缆的Cable Modem技术是最有潜力的。 ADSL具有上下行速率不对称的特性,因此其应用主要适用于为用户提供上网服务以及VOD点播等业务,而不适用于局域网互联业务。提供因特网接入业务采用“ADSL+ATM/以太网”的方式。用户端配置ADSL远端设备,局方配置DSLAM(ADSL局端设备),它们之间用普通电话双绞线进行连接。ADSL远端设备为用户PC机提供以太网接口,DSLAM通过ATM或快速以太网与ISP相连。通过该网络,用户就可以实现宽带接入因特网。DSLAM可以放置在ISP机房,通过接入网接入到ISP;也可以直接放置在ISP机房,与ISP接入平台利用局域网直接相连。利用ADSL提供VOD视频点播业务则可以采用“ADSL+ATM”的方式。     

ADSLDSLAM上行方式的比较

ADSL以其自身的技术优势为电信网络运营商打开了一扇通向未来的大门，在近一年内的城域网接入建设中取得了快速的发展。就ADSL接入的底层协议来看，有ATM和．P两种，这两年ADSL接入技术主要采用ATM的底层协议，主要是由两种技术的成熟度、芯片成本以及终端调制解谭器的兼容性决定的，但是近段时间．P内核的DSLAM也开始进入市场；就上行方式而盲有A7M和0P两种，ATM上行多采用ATM 155Mbit／s方式，3IP上行多采用100Mbit／s以太网方式，ATM内核和IP内核的DSLAM都可提供0P上行。本文主要讨论ATM上行和IP上行两种方式，以下简称ATM DSLAM和IP DSLAM。     

SHDSL接入技术与网络应用

基本的SHDSL线路传输系统由局端收发送器STU—C和远端收发送器STU—R组成．通常局端STU—C集中放置并提供网络侧上行接口形成局端接入复用器DSLAM设备．而根据系统所采用传送模式的不同．DSLAM设备提供的上行接口要求应有所不同：对于TDM传送系统，DSLAM设备通常采用TDM-E1-G703电接口；而对于ATM传送系统，DSLAM设备则通常采用ATM—STM-     

ADSL组网技术设计和相关问题的探讨

由于ADSL的独特优势和在电话网方面的优势,目前传统电信运营商主要采用ADSL技术提供宽带接入。ADSL网络主要由电话双绞线／光纤、ADSL节点、宽带ATM网络和宽带接入设备等组成并最终接入IP城域网,ADSLDSLAM有ATM上行和IP上行2种类型,ADSL用户可采用ADSL拨号和ADSL专线2种方式接入Internet。本文结合ADSL网络实际情况和笔者参与ADSL工程和系统集成的经验,讨论了ADSL的组网技术,包括城域网与BRAS的互联、BRAS与ATM的互联、DSLAM与ATM之间的互联设计、ADSL终端用户的接入,以及ADSL组网中需要考虑的因素和存在的问题等,针对优化网络、提高维护质量和发展宽带业务提出了一些解决办法和建议。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

A rigorous proof of MIMO channel capacity’s increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output（MIMO） communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas. The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.     

Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers

A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers(M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Home-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.     

Diode-end-pumped Nd:YVO4/LBO lasers with 4.2W continuous-wave output at 457 nm

A continuous-wave (CW) 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd: YVO4 and using LBO as the intra-cavity SHG crystal With the optimization of laser cavity and crystal parameters, the laser operates at a very high efficiency. When the pumping power is about 31 W, the output at 457nm reaches 4.2 W, and the optical to optical conversion efficiency is about 13.5% accordingly. The stability of the out putpower is better than 1.2% for 8 h continuously working.     

Call for Papers

正Wireless Body-area Networks The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless personal networks