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有线电视宽带网络结构

2018-08-07 23页 doc 68KB 21阅读

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有线电视宽带网络结构有线电视宽带网络结构 1. 概述 光技术的快速发展给有线网络带来了革命性的变化,有线网络需要考虑所有业务(E-mail、语音、视频等)的基带传输(模拟的和数字的)以及IP数据传输的特性。问题的关键是能提供一个灵活的、可升级的而且在未来若干年内能够使用的网络。有线电缆正通过提供新的和强制性的业务来解决这 “最后一英里”的问题。 本文的焦点是放在物理层或者实际的网络。与任何其它的网络相比,宽带有线电视使光纤应用于网络之中。其目标是建成特定宽带业务网。有线网络开创性地把光纤和传统的同轴电缆结合在一起成为一个混合网络。这个混合光...
有线电视宽带网络结构
有线电视宽带网络结构 1. 概述 光技术的快速发展给有线网络带来了革命性的变化,有线网络需要考虑所有业务(E-mail、语音、视频等)的基带传输(模拟的和数字的)以及IP数据传输的特性。问题的关键是能提供一个灵活的、可升级的而且在未来若干年内能够使用的网络。有线电缆正通过提供新的和强制性的业务来解决这 “最后一英里”的问题。 本文的焦点是放在物理层或者实际的网络。与任何其它的网络相比,宽带有线电视使光纤应用于网络之中。其目标是建成特定宽带业务网。有线网络开创性地把光纤和传统的同轴电缆结合在一起成为一个混合网络。这个混合光纤同轴(HFC)网络对于有线网络来说具有战略上的重要性。光纤把模拟和数字电视从前端向终端发送。该技术目前可把光纤信号往用户家庭的几英里范围内发送。同轴电缆再把宽带业务传送至家庭。最后一英里的同轴电缆被用于支持譬如电话之类的可选业务的传输媒体。 有线运营商已经把同轴电缆网络进行升级以支持双向通信,从而使用户可以享受他们的多项服务,这当然要追加投资。当新的HFC网络完全实现后,将具有许多好处,它们包括: •有线电话的能力 •高速Internet接入 •有线电视频道数目的增加(超过200个模拟的和压缩的数字频道) •利用机顶盒的视频点播(VOD)能力 •交互式电视 •为满足新的数字电视标准而建立的基础结构,所有标准都是基于HFC骨干网。 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 本文将阐述两种HFC网络结构,“供电范围节点”(PDN)和“小型光纤节点”(MFN)。PDN结构或类似的变种是北美配置的HFC网络的主要代表,它能支持许多新的业务。PDN与其它HFC结构的不同之处在于,节点的大小并不是由固定用户数决定的,而是由光纤节点接收机的数量决定的。RF放大器和网络用户终端可以由单个网络供电(AC)。MFN是网络发展的下一步,它表现了一个深层次光纤结构。MFN是非常重要的,因为它可去除同轴有线电缆段上所有的放大器(除了必不可不的以外)。这不仅仅增加了可靠性,而且还保证了宽带业务所需要的带宽。首先,本文将定义一些术语和有线电视产业和正在建造的HFC网络的相关信息。 2. 传统的同轴有线电视网络 一个简单的有线电视系统从前端到终端,包括接收卫星等电视信号源的接收设备。从这些源来的信号将通过有线网络发送。然后被放大,再把模拟视频传送给传统的全同轴有线电缆网络。 有线电视系统是基于载波的,每套节目均占用一个载频。载波的幅度是不断变化的,这叫幅度调制(AM)。所有的视频信道将在一个频分多路复用器(FDM)内合并起来,北美每个载波距离是6MHz。有线电视系统以两个方向传送信息,一个是向用户传送,称为前向路径(或称下行),另一个是从用户那里来,称为反向路径(或称上行)。在美国,前向信道被放置在54MHz以上的频率上,而5到42MHz之间的频率就被分配给反向信道。 显示了一个代表性的有线电视袭用的传输频谱,它的前向路径信道达到了860MHz。在前向路径,模拟信道是从54到550MHz,而数字信道是从550MHz到860MHz。 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 有线电视网络是由三个主要部分构成的:干线、馈线和引线。干线是用于覆盖广大的距离,经常超过10英里。当干线是由同轴电缆组成时,那么每2000英尺就需要一个放大器。令人吃惊的是,有线电视系统的干线部分只占了整个系统总长度的百分之十二。放大器的级联限制了带宽,典型的级联具有20到40个放大器。因为每个放大器都是有源部件,所以每个放大器都会给信号加入噪声和非线性失真,并且会带来放大器链的不可靠性。 有线电视系统的馈线部分面向用户的接口。它最大的长度约为1.5英里。这一限制是因为RF能量被分配对各个家庭进行馈送。因此,RF电平与在长距离干线部分的电平相比,要相对更高一些。这些更高电平进入了放大器的非线性区。结果,导致质量指标下降。在有线电视系统中,大约百分之三十八的长度是馈线部分。 引线是从分散的馈线进入家庭的同轴电缆。它最大的长度为400英尺,但在典型情况下要少于150英尺。一个有线电视系统中的大约一半的长度是引线和家庭中的布线。有线电视系统中的馈线部分是变化很平凡的部分。每天都有新的用户增加,和老用户退出。美国每年大约有20%的人搬往新的住处。这样就造成20%的用户数波动。对于馈线而言,支持这一持续不断的用户数波动是非常重要的。它必须使网络具备工作有效性、物理健壮性并且易于配置。 图1. 一个有线电视系统传输频谱 放大器被用于补偿传输电缆和信号分配器、分支器的频率失真。因为放大器的电路是单向的,所以放大器单元必须先在两个方向上分离信号流。信号分离是利用双工器电路进行的。在经过双工之后,每个信号被放大,然后利用同样的双工器连接到同轴电缆上。 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 总而言之,这些早期的有线电视网络向用户发送模拟视频信号是非常好的。但由于放大器的级联,这些网络并不适合于实时的双向高带宽业务,最主要的是网络中单收集点聚集所有回传信号的漏斗效应。使之从80年代中期陆续开始实施光纤同轴电缆混合(HFC)传输结构。 3. 混合光纤同轴(HFC)有线电视系统 因为有线电视和通信公司不断努力引入新的业务,必须找到一个合理的成本提高网络容量的方法。这个困难问题的一个极其出色的解决,就是HFC系统中的光电子学的实现。光电子学技术在高容量交互式多媒体传输所需的HFC网络的发展上具有极其巨大的影响。这种技术的引入使得最初为视频业务而的网络能够为各种交互式视频、数据和语音业务提供可靠的带宽。 HFC结构使以一种成本高效的方式提高带宽、信号质量和可靠性成为可能,这种方式能够减少维护成本和保持操作人员界面友好性。它使两种业务成为现实。在干线部分覆盖低损耗的光纤能够去除干线上的放大器。这也就使同轴电缆大大缩短,典型的是四到六个放大器。这样带来的好处包括大大减少放大器中断的脆弱性、减少带宽限制和由于放大器串联而导致的噪声积累,以及大大简化输入部分。采用双向传输有两个原因。第一,光纤本身不再是干扰信号的入口了。第二,有线电视系统被分割成大量的小型有线电视系统,而且这些小型系统彼此隔离。如果在某个小型有线电视系统入口形成干扰的话,该干扰将不会削弱整个有线电视系统其它部分的性能。 有线电视信号的光传输用单模光纤来完成,该光纤在1310nm的波长处大约有0.35dB/km的衰减,在1550nm的波长处大约有0.25dB/km的衰减。激光波长的选择是基于网络设计标准,包括成本、模拟性能以及传输距离要求等。iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 光纤的衰减在合理的温度范围内是固定的,而且与RF频率无关。 引入HFC网络的光节点或者光纤节点(FN),经常被安放在户外,譬如一个基座上或者悬挂在架空绞线上。光纤节点接收光信号,把它转化为电信号,并放大,然后向本地用户发送。在返回方向上,节点收集5-42MHz带宽范围内的信号,并把它们以光的方式传送回前端进行处理。在 “传统”的HFC网络中,每个光节点名义上服务500-2000个家庭。核心网络驱动器是低成本的,而且在噪声和失真方面对模拟视频信号有良好的性能。终端用户可以接收到经模拟视频残留边带(VSB)调制的78个RF信道。收费频道的可选择控制和收看前预付费通过用户机顶盒终端实现。 HFC结构的主要优势之一,是用户数可增加,并以多种格式携带多种类型信息的能力。 HFC有线电视网络和电话网之间的区别是可用宽带宽传送模拟电视。在美国,大约有3亿模拟电视机在使用,基本上都接入了有线电视。实际上,在这个国家有电视的家庭比有电话的家庭多。HFC为利用低成本电视发送设备提供了充足的带宽。 要达到这些目标,需要四种关键技术: •高能量的1550nm光纤可用于携带交互式数字电视并经“多电平正交调幅”(M-QAM) 的载频信号,以及为简化光纤结构而降低网络成本的接入技术。 •利用同步光纤网络(SONET)多路复用器来进行综合数字业务传输,对于建造高速多媒体接入网络是非常关键的。 •波分复用(WDM)和密集波分复用(DWDM)不仅仅增加带宽,而且还用于光路由和降低接入成本。 •当网络光纤数量不断增长时,无源光技术对成本和性能有着极其关键的作用。 决定最佳接入结构的是足够的带宽宽度, 这对于广播和交互式小范围广播而iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 言是必须的。HFC网络有四个与传送交互式带宽有关的因素:频率、空间多路复用、光谱效率以及光波长。 频率决定通道大小(750MHz、862MHz或1GHz),以及决定副载波提供什么类型信号的能力。每个频率都可以当业务设置改变时,随时使用,这与其它结构相比提供了一种独特的灵活性。空分复用决定了骨干网中的光纤是如何运行和如何达到每个节点的,以及如何装载它们。频谱效率允许随256-QAM或64-QAM调制技术改变,这些技术能够有效地提高频谱利用率。最后,多种光波长,不管是DWDM或者1310/1550的结合,都可以用于一个特定的光纤中以用来提高容量。 处理好HFC反向信道是极其重要的。为了解决潜在的光纤性能的问题,Fabry Perot(FP)和无冷却分布式反馈(DFB)激光现今均被用于网络中,靠的是业务数量的增加和性能的提高。从前端到用户端距离一定时,光纤配置得越长,网络对电入口的影响就会越小。由于光纤被配置得很长以进行前向传输,使RF的级联长度缩短,提高了可靠性和降低了成本。 对于语音和数据而言,通常的选择----至少在目前----便是SONET技术。但是SONET在视频传输方面的效率并不高。把一个或多个视频信号压缩至数字业务第三层次(DS-3)速率的视频编解码器的成本很高,而且与传统传输系统相比,它们的性能规格比更差。此外,SONET网络管理使用的是DS-3电路,它无法自我监视视频性能。因此,许多宽带运营商就安装了两个并行的网络:一个用于语音和数据的SONET网络, 另一个用于视频的专有数字系统。为了解决基本的传输问题,要安装SONET多路复用器。 4. 供电节点 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 几年前,有线电视运营商开始从事于一项全国范围内的,把系统升级为 “全业务”HFC网络。在那时,节点的大小根据固定用户数设置,最初可能是2000、1000或500个家庭。当然,节点的大小是受放大器级联限制的,这样可以确保产生的噪声和互调指标极限不超标。但在高密度区域内的节点经常遇到超过500个用户 (一直到800个用户极限),但是在低密度区域的节点经常由于级联的限制大大少于500个用户。 一个提供干线电话业务的有线电视公司,利用分布式拓扑技术,采用传统的90V AC供电(PS),50%的负荷。对90V供电方案中,超过4000英里干线的分析表明,许多节点需要三个PS,并且平均每节点大约要达到2.5PS。对许多节点设计的更进一步的考察指出,供电必须加强,以便能承受住两个PS无法处理的负载量。对PS相对来说负载较轻(少于它名义上额定值的50%),明显处于低效状态。供电增加了系统操作和维护的麻烦,而且对网络可靠性有不良的影响。 一个更新的HFC升级结构可提高效率,并达到以下目标, •减少HFC网络系统升级的资本花费 •提高网络可靠性 •减少系统运作和维护的成本 •提高前向和反向的带宽,并提高模拟信号的质量 •通过减少升级系统的时间和花费来缩短打入市场的时间,并确保新的节点提供更高级的业务。 网络供电问题在节点大小策略的讨论中占有中心的地位。如果节点变的很小以至于它的功率负载不能够有效地消耗电能供应的容量,那么通过多个节点聚集功率,来获得比较经济实惠就变得非常值得。这便设计出一个功率分布系统(譬如 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to “功率馈线”电缆),它的安装是非常便宜的,但是对于减少传输电缆中的能量浪费却是足够有效的。 PDN定义了由PS支持的最大用户数量的节点大小。这正好与以前的设计形成对比,在后者中节点的大小或者是由覆盖范围内的家庭的固定数目定义的,或者由级联的放大器数量的限制定义的。 人们对更大型的节点有趣的观察,用于这些节点的总AC功率经常达到用于单个15amp PS的期望的75%的负载因数。这种情况发生在高密度区域内,在这些区域内,大量的家庭被少量的级联所覆盖,而且有线电话网络接口单元(NIU)的功率负载是与每英里的NIU的数量成比例的。 人们立即意识到PDN结构中的节点大小是极其重要的, 这对设计师提出新的挑战,把多大范围的区域隔开以便在不过载的前提下, 对节点进行供电。 与每节点具有500个家庭的传统设计相比。在PDN的设计上具有一定积极的影响,所有这些都在中密度和高密度的早期节点设计中被证实: •每英里干线上放大器的数量大约减少15%到20%左右,可以大大提高干线延伸的长度。 •节点的数量提高50%到75%,能提高低密度区域的比例 •备用能源供应的数量大约减少20%到30% •平均能源供应负载因子大约提高10%到15% •减少同轴电缆覆盖,从目前的15%到25%的范围减少到少于5% •提高光纤覆盖的用户数量,提高幅度少于5% PDN的设计者们很自信地认为,这样对于成本的减少将在中密度和高密度的区域变得非常普通。但是在低密度区域(每平方英里少于75个家庭)成本的减iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 少将变得更加困难,因为需要更大的光纤覆盖的比例,以达到100-250个家庭的节点。但是现今的HFC-500结构中几乎没有低密度节点能够达到500个家庭,因为级联的限制。 5. PDN结论 网络设计者正在把供电从最初的15安培输出容量到18安培,最终到21安培。因为骨干网络很可能安排电话和高速数据的传输,所以对网络升级必须做到 “热交换”的方式和完全无业务中断的方式。 PDN是一种较好的HFC解决方案,它能够很好地降低初装费、运作的成本以及提高网络性能和可靠性等方面的问题。这对中等密度和高密度区域系统的吸引力是非常大的。 6. 微型光纤节点 提供无限带宽的光纤,配置得离用户越近,则能提供越多的业务量和性能越灵活。DWDM技术促使扩大光纤的覆盖范围。例如,HFC网络中的光纤数量在过去的12年中不断增长,从光纤骨干网结构的5%到MFN结构的30%。 DWDM技术与数字信号处理(DSP)以及RF技术,在网络操作和业务方面提供了更大的灵活性。这种趋势将会继续下去,而且有线电视将会通过这些机会得到更大的益处。 PDN把光纤延伸致用户有源放大器的范围之内。微型光纤节点使得更深层次的光纤渗透,,以及使网络中高级光子技术的开展应用成为可能。其目标是, •建立起一个能经受住未来考验的网络 •继续简化操作并减少运营成本 •极大地提高网络可靠性 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to 所有这些考虑都会导致工业界,对于HFC网络解决方案的持续不断的定义,和重新定义,目的是为了捕捉新技术解决方案、业务需求和可实施性(成本利益比)的不断变化的前景。 随着光纤的不断深入的延伸,关键的结构问题,就变成了如何利用HFC网络的同轴电缆的最后一英里。光纤延伸的结构使节点大小变为50个家庭,这与一个有500个家庭的节点相比,就能够使用户潜在地产生多出10倍的交互带宽,这是由于具有了使用小范围广播频谱的能力。AT&T宽带已经提出了这样一个网络的实现计划,并把它叫做LightWire结构。在这个结构中,同轴电缆段基本上所有的放大器都被去除了(除了那些在节点接收机内部的)。只有无源的同轴电缆才被用于向用户家庭传送信号。这种最终的同轴电缆也被用于电路交换或IP上的语音(VoIP)业务的家庭终端的网络电力供应。这种结构特性保持了对各种不同信号格式和协议对整个HFC网络的透明性,因此它完全支持目前业务的已有的操作。 工业界面临的另一项挑战,是在减少不断增加的成本的同时,为未来的业务扩展和增长提供灵活性。为了解决这个问题,在它们的地理位置的基础上,MFN与三条光纤以雏菊链的方式相连,一个携带下行流的广播信号,一个携带剩下的下行流小范围广播信号,一个携带上行流信号。这种拓扑技术实现了光纤总线(物理的)结构。它的好处是简化了处理并减少了相关成本,以及带来了未来扩展的灵活性(光纤总线以后可以扩展以覆盖更多的区域)。分析显示,这种结构的成本与传统的HFC网络的成本相同。 在物理总线的基础上,逻辑星型或总线操作都可以实现。譬如在使用反向传输的情况下,每个MFN能够进行循环功能以实现总线操作。另一方面,利用iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to WDM技术,逻辑星型可以由不同波长携带的每个MFN来实现反向传输。 7.结论 线性光波技术使得在HFC基础结构上的RF副载波链路得以实现。这种端到端的透明链路,为有线电缆提供了许多不同的业务传输和新的业务机会。本文中举例说明的PDN和MFN是HFC网络结构的两个高级的例子。 MFN的下一步甚至会更加令人兴奋。这种网络将使得HFC有线网络能够向用户提供接近对称的数字带宽,包括向住宅用户和商业用户提供交换10Mb/s和100Mb/s业务的能力。这种额外的带宽将通过减少有线电视系统上的模拟信号的数量来获得,为数字业务释放出更多的容量。这些数字业务将包括视频和数据。 这些网络将显示出无源光网络(PON)的许多特性,但是成本却低得多。不但新的业务机会将成为现实,而且网络本身也将变得更加可靠。 为了达到端到端的可管理宽带业务的潜能,基础网络必须发展成能够支持几乎无处不在的高速对称带宽。有线HFC网络正处在提供这些能力的轨道之上。随着光电子技术的不断发展,HFC将能够提供最容易升级的高带宽网络。 iodine lamp fixed set up to ensure security. Thallium metal halide lamps and sodium installation height should be more than 5M. Light wire shall not be closer to the surface of the lamp. 3) overhead lines (1) overhead lines must be located in a dedicated pole (concrete, wood), set up in a tree or on the scaffold is strictly prohibited. (2) overhead line insulators for crossarm and should be installed, specifications, line distance, span shall conform to the requirements of overhead lines, pole line from 2.5M to be insulators. (3) overhead lines should generally be 4m off the ground, the motorway for more than 6m. 4) electrical box (power distribution boxes, switch box) (1) electric box doors, locks, color and number. (2) switching apparatus within the electrical box must be intact, the wiring is correct. Contact motion sensitive and reliable. Well insulated. Without dust, debris, box may not be skewed. (3) electrical box mounting height and insulation materials shall be subject to regulations. (4) within the electrical box settings leakage protection, use reasonable rated leakage current is extremely fit. (5) the distribution box shall have a main fuse, dissolve, separate production. 0 rows row is complete. Power and lighting equipment, respectively. (6) the distribution box switch should be combined with distribution line or switch box correspond to one by one, tap Settings, to ensure that the road under; the total rating of the switch and the tap switch values, setting value fit. Echo power equipment fuse matches the actual load. (7) metal box should be grounded, or the zero connection protection. (8) the switch boxes and electricity equipment in one machine with a gate and a insurance. (9) to move the same switch box is equipped with two voltage 380V and 220V level is strictly prohibited. 5) ground zero (1) grounding angle steel, steel or steel pipes that are available, but not ... Inspection records, and to
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