通信专业外文翻译---基于EPON的三网融合接入网技术

基于EPON的三网融合接入网技术
1引言
信息社会的发展使人们越来越离不开网络技术提供的便利，经过最近20年的快速发展，我国电信网、有线电视网和互联网都已经成为世界第一。

目前，我国有线广播电视网已有333万km光缆线路，1000万km同轴电缆线路，有线电视用户数达到1.75亿户，其中数字信号电视用户6500万，模拟信号电视用户超过1亿户，有线电视网络提供的宽带接入用户数300多万户。

2009年，基础电信企业的互联网宽带接入用户净增2034.7万户，达到10322.6万户，宽带网民数达到3.46亿。

通过对比可以发现，最大程度地利用现有网络资源，用较小的投资进行双向改造，迅速发展宽带用户，是广电行业面临的巨大挑战和历史机遇。

随着国务院对三网融合政策的批复，有线电视网向前演进为下一代广播电视网（NGB）的浪潮已经不可阻挡，NGB的骨干网和内容平台都已经有相对成熟的解决方案，接入网络的建设由于解决方案的复杂性和占总体投资比例的重要性而成为当前NGB建设的重点和难点。

2接入网技术方案
EPON技术由于高带宽、易维护、远距离覆盖的特点成为当前FTTx的主流承载技术，目前产业链发展完善，是电信运营商接入网络建设的首选技术。

但是由于在驻地网层面采用光纤直接到户的成本较高，传统电信运营商基本上采用了FTTB+LAN或FTTB＋DSL的方案，这样在尽量节约驻地网投资的前提下，获得了最佳的网络性能。

广电运营商长期专注于HFC网络的建设，拥有着庞大的HFC接入网络，利用HFC作为入户媒介可实现最大的实用性和经济性。

广电HFC网络中的同轴电缆网是一种理想的数据传输媒介，尤其在最后100m的带宽支持能力远远高于五类线或电话线资源。

因此，在广电网络双向改造中如何融合光纤和HFC两种介质，深入挖掘现有网络价值，被广电运营商所关注。

目前比较经济可行的双向改
造技术方案有3种：CMTS，EPON+LAN和EPON+EoC。

2.1 CMTS适合稀疏模式网络覆盖区域
CMTS利用现有的有线电视网络，通过对信号进行QPSK/QAM调制，在HFC低频端进行双向传输。

CMTS的优点是技术较成熟，网管能力强，可实现大规模双向覆盖。

缺点是CMTS噪声汇聚效应影响系统的带宽和性能，同轴电缆及接头质量要求较高，后续维护工作量较大；对于大多数有线电视运营商而言，上行噪声是一个普遍存在的问题，尤其是在低频带。

CMTS设备包转发能力弱，无法满足日益增长的高带宽业务需求，可承载业务有限，无法提供全业务承载，后续系统扩容成本巨大。

CMTS的Cable接入属于共享线路方式，如果只作宽带接入和上网，在用户数量不太多的情况下比较适合广电开展数据业务。

对于目前国内用户集中居住，用户需要长时间占用网络、大流量吞吐数据，单位带宽下降明显，不利于高带宽业务的开展，采用CMTS实现大范围的用户宽带接入不够经济。

2.2 EPON+LAN适合于高密度用户新建小区
EPON+LAN方案是通过EPON网络接入到楼宇，通过ONU提供以太网接口，用户接入通过以太网五类线实现。

采用这个方案实现用户语音和互联网接入，有线电视信号仍通过HFC线路实现。

它的优点是技术成熟，设备商较多，接口和标准规范。

该方案适合于高密度用户和大带宽业务需求新建小区的第一次综合布线时一次完成，而对于已经开通有线电视的老用户需要重新进行布线，小区楼道和入户布线施工难度较大，用户一般不愿意接受。

2.3 EPON＋EoC适合现有CATV用户的首选技术
EPON＋EoC技术是在现有的HFC网络基础上构造一个适用于广电网络系统的数字带宽用户接入网络，它在不影响现有的CATV正常工作的前提下，以先进的调制解调技术，将以太网信号合成在同轴电缆中与原有的CATV信号一起传输，用于承载基于IP的数据、语音和视频等业务。

它以较少的改造成本和
工程量将原来单向的有线电视网络改造成为一个双向的、能够承载多种业务的双向宽带网络。

采用EoC技术具有良好的适应性和灵活的组网方案，充分利用了广电原有的同轴接入网资源，节省了入户部分的线路投资。

将EPON技术和EoC技术相结合，统一网管，组成整体解决方案，可以为广电三网融合NGB的发展提供接入网络的最佳技术。

EPON＋EoC可提供数据、视频、语音于一体的三种播放的综合承载，通过一张接入网提供过去多张网络的功能。

该方案在开发过程中充分考虑中国国情和当前广电网络的实际情况，在驻地网层面利用广电网已有的Cable网络作为传输介质，节约了大量的综合布线成本和运维投资，兼具高性能和低成本。

EPON＋EoC技术满足了广电数字电视的双向改造和国家三网融合的需要，将推动NGB产业在中国的深入发展，是面向广电运营商NGB网络接入层首选技术。

3 EPON和EoC组网技术
3.1 EPON技术
光纤作为传输高速率、大容量、多业务的最佳媒质，早已在骨干网和城域网中得到了广泛的应用，在接入网层面，光纤也已经得到了普及与应用。

光纤具有寿命长、可靠性高、抗干扰性强的优点，光传输具有很强的带宽扩展能力，并且容易实现各种业务平台的融合。

EPON技术是将以太网与无源光网络相结合的技术，按照IEEE802.3ah国际标准可以支持1.25Gbit/s对称速率。

作为光纤接入网的重要解决方案，EPON技术具有ADSL，LAN等无法比拟的特性，也比APON，BPON，GPON等技术更为高效地满足了“EverythingoverIP”的多业务接入需求。

EPON接入网络具有投资成本低、操作和维护简单等优势，为运营商解决“最后一公里”问题提供了一种非常经济有效的宽带接入解决方案。

目前，EPON技术已经在国内外得到了大规模的应用，得到国内外运营商和厂商的支持和认可。

通过EPON系统设备，利用FTTH/FTTB光纤网络覆盖家庭、企业用户可以提供最大带宽达1Gbit/s的传输速率。

运营商可以用经济的造价和极少的光缆线路投资，方便地实现高速上网，IPTV组播/点播等高带宽IP数据业务的传送。

EPON系统主要由OLT（OpticalLineTerminal，光纤线路终端）和ONU （OpticalNetworkUnit，光纤网络单元）以及分离器（Splitter）构成，OLT提供到IP城域网，IPTV承载网，NGN软交换网上行接口。

针对最终用户不同的业务需求，运营商可灵活选择终端ONU设备，满足FTTH/FTTB/FTTC/FTTC+EoC 等多种应用场景。

典型的EPON组网方案如图1所示。

图附-1 EPON典型组网方案
Fig attached-1 EPON typical network scheme
3.2 EoC技术
EoC是指在同轴电缆上传输以太网数据的技术。

EoC系统由头端、终端、同轴分配网等部分组成。

头端一般放在光节点位置，起分发上层以太网数据、汇聚终端设备的作用；终端放在用户家里接入用户电脑或互动机顶盒；同轴分配网络
是从有线电视网光节点位置到用户家里的网络，除了同轴线缆以外，还包括有源放大器，EoC跳接器，分支/分配器等设备。

目前常用的EoC头端设备是基于HomePlugAV技术的有源调制的接入汇聚设备，它的主要功能是将数据基带信号以OFDM方式调制到7～30MHz频段，再与有线电视网络信号进行混合后在有线电视HFC网的同轴电缆上传输。

常用的EoC用户端设备是基于HomePlugAV技术的用户端的调制解调设备，其主要功能是将各类用户终端设备电脑，机顶盒，IP话机等，接入到EoC系统中，实现以同轴电缆为介质的双向宽带接入。

针对广电运营商的EPON和EoC技术，OLT放置在网络系统的前端，ONU 放置于楼层，连接EoC（EthernetoverCable）局端设备，通过HFC入户。

用户通过有线电视同轴电缆线传输和接收数据信号，同时不影响有线电视信号的传输和接收。

EoC主机最大带宽可达80M以上，最多可带64个从机，多个从机共享主机带宽。

主机在连接一定数目从机的情况下，从机的带宽可自动调节，用QoS 可设置从机的带宽，主机可进行SNMP网络管理。

桥接器可以延伸有线电视信号的传输距离，跨接各种有线电视信号放大器，实现数据双向传输，真正实现数据信号和电视信号一线传输。

目前EoC主流产品采用HomePlugAV/BPL技术，EoC头端设备为缆桥交换机，缆桥交换机是同轴数据网中对有线电视单向放大器跨接的设备，它将混合后的信号通过频率分割的方式，使数据信号不经过放大器，有线电视信号经放大后通过跨接器再次与数据信号混合。

缆桥交换机采用模块化设计，主要模块有CATV模块，ONU模块，EoC头端模块，主控交换模块。

这些模块都作为可选模块配置在相应的机箱里。

其中主控交换模块只有在多端口缆桥交换机中才有应用。

模块化设计的好处在于，可以更加灵活地满足广电运营商不同时期的需求和远期的灵活扩展，最大限度地降低投资成本，获得高回报。

不同地区的运营商可根据经济发展情况、用户密度、覆盖率、开通率和用户的带宽需求情况，选购不同接口数量的缆桥交换机，安装场合可以选择室内或室外。

用户终端设备按网络接口的数量主要分单接口、双接口和四网络接口。

EoC
头端模块数量可以根据需要进行配置，每个模块提供一路电视信号输入和一路Cable混频口，可同时传输和接收数据信号和有线电视信号的混合信号。

CATV 接入模块支持单CATV接入口，提供一路有线电视接口，可传输有线电视信号。

主端通过耦合器可以支持多路下连同轴通道。

采用高性能的光器件，分光比为1：32时覆盖距离达到20km，分光比为1：64时覆盖距离达到10km。

分光比为1:64时平均带宽可以达到15Mbit/s，满足用户的带宽需求。

3.3 EPON+EoC组网应用
采用EPON和EoC技术对传统有线电视网络进行技术改造，可利用EPON 设备完成光缆干线的双向改造、用户同轴电缆接入网双向改造，使用有源EoC 进行组网，在ONU下接有源EoC头端，覆盖光节点之下的所有用户，对有双向需求的用户使用EoC用户端接入。

这样将单向广播式传输网建设为双向传输网络。

EPON＋EoC的典型应用组网方案如图2所示，缆桥交换机放置于楼道或室外，覆盖一幢大楼或一个单元。

现网已铺设光节点，缆桥交换机不用配置CATV 模块，通过射频电缆接入到缆桥交换机，ONU模块配置在缆桥交换机，实现数据或互动电视信号的回传。

图附-2 EPON＋EOC应用组网方案
Figure attached-2 EPON + EOC application network scheme 如果现网由于光接收机下移，缆桥交换机需要集成光接收功能。

这时缆桥交换机需要配置CATV模块，通过光纤将电视信号接入到缆桥交换机。

ONU模块配置在缆桥交换机，实现数据或互动电视信号的回传。

另外一种情况，如果现网已铺设光节点，ONU放置在楼外，接入几个单端口的缆桥交换机，数据信号通过线缆接入到缆桥交换机，实现数据或互动电视信号的回传，电视信号通过射频电缆接入到缆桥交换机。

4结束语
广电运营商采用EPON和EoC技术有助于综合利用网络资源，快速完成NGB接入层的建设，实现数字化双向化改造，减少大量重复建设，节约建设和运维成本。

采用EPON＋EoC方案，用户无需对室内布线做任何更改，只需增加CNU终端设备就可以实现双向、交互、多功能、多业务，享受三网融合带来的丰富内容。

EPON＋EoC方案能够全面提升有线电视网络技术水平和业务承载能
力，发挥有线电视网频带宽、低成本、易普及的优势，使有线数字电视成为进入千家万户的多媒体信息平台。

双向改造后的有线电视网络是承载、提供三网融合业务最重要的网络，将成为现代社会活动中最重要的信息通信基础设施。

广电网经过双向改造，采用光纤加同轴电缆的接入方式能为每个家庭用户提供可扩展的宽带接入，可以满足标清和高清电视节目的带宽需求，用户欣赏到的画面质量将更锐丽逼真，图像更清晰。

通过这条“高速路”用户可以快速方便地处理日常的信息，畅享信息社会的便捷服务。

附录C 外文文献
Based on the three nets fusion EPON access network technology
1 introduction
The development of the information society to make people more and more from the network technology provides convenience, and over the last 20 years of rapid development, China telecom network, cable television and the Internet are all has become the world's first. At present, our country has 3.33 million km cable radio and television network fiber optic cable line, 10 million km coaxial cable line, cable TV subscribers of 175 million users, including digital signal television subscribers 65 million, analog TV users and more than 100 million, and the cable TV network provides broadband Internet more than 300 households. In 2009, telecom enterprise Internet broadband user stood for a total of 103.226 million, and the number of broadband Internet users reached 346 million. By contrast, it can be found that the maximum use existing network resources, with less investment for two-way transformation < /zt/shxgz/index.shtml >, and quickly develop broadband users, is the radio and television industry's challenge and historic opportunity.
With the state council on three nets fusion policies written reply to a subordinate body, cable TV networks broadcast TV networks for the next generation forward evolution (NGB) has been unstoppable tide, NGB backbone and content of the platform has a relatively mature solution, access network construction because of the complexity of the solution and overall investment proportion of the importance of the construction of NGB and become the key and difficult.
2 access network technology solutions
Due to high bandwidth EPON technology, easy maintenance and long distance covered become the mainstream of FTTx characteristics of bearing technology, at present developed industry chain, telecom operators access network construction is the first choice of technology. But because the local nets level by using optical fiber to the home directly the cost is higher, the traditional telecom operators basically used FTTB + LAN or FTTB + DSL solutions, such as saving in local nets investment, under the premise of won the best network performance.
Radio and television operators long-term focus on the construction of HFC network, with huge HFC access network, use of HFC as entering a media can achieve maximum practical and economical efficiency. Radio and television HFC network of coaxial cable nets is a kind of ideal data transmission medium, especially in the final 100 m bandwidth support ability is far higher than the five kinds of line or telephone line resources. Therefore, in radio and television networks two-way renovation of optical fiber and HFC how fusion of two kinds of medium, research the existing network value, be cable operators paid more attention to. At present more economical and feasible two-way reconstruction technique scheme has 3 kinds: CMTS, EPON + LAN and EPON + EoC.
CMTS 2.1 for sparse network coverage area mode
CMTS use of the existing cable TV network, through to the signal QPSK/QAM modulation, the low frequency in a two-way HFC transmission. CMTS is the advantage of technology are more mature, network management ability is strong, can realize large-scale two-way covered. Defect is CMTS noise gathering effect system bandwidth and performance, coaxial cable and joint quality the demand is higher, the follow-up maintenance larger workload; For most cable TV operator speaking, uplink noise is a widespread problem, especially in the low frequency band. CMTS package equipment transmit ability weak to meet the increasing high bandwidth business
requirements, can carry business Co., LTD, cannot provide the full service bearing, the follow-up system cost huge expansion. CMTS Cable access belongs to share the line way, if only for broadband access and the Internet, the number of users in not too many cases comparison for radio and television in data services. For the present domestic users concentration living, users need long time takes up the network, big flow data throughput, unit bandwidth down significantly, go against the development of high bandwidth business, the wide range of users CMTS realization of broadband access is not enough economy.
2.2 EPON + LAN suitable for high density users new district
EPON + LAN scheme is through the EPON Internet access to the building, through the ONU provide the Ethernet interface, user access through the Ethernet five kinds of line realized. Using the methods of speech and user access to the Internet, cable TV signal is still through the HFC circuit implementation. Its advantages are mature technology, equipment business more, interface and standards. The plan suitable for high density users and big business needs the new bandwidth first comprehensive wiring once completed, and to have opened the cable TV old users need to restart the wiring, the corridor and in-home wiring construction difficulty bigger, users generally don't willing to accept.
2.3 EPON + EoC for the existing CATV users first choice of technology
EPON + EoC technology is in the existing HFC network structure is based on a in the radio and television network system of digital bandwidth users access network, it has no impact on the existing CATV normal work, under the premise of with advanced demodulation technology, will Ethernet signal synthesis in the coaxial cable with the original CATV signals in together the transmission, and used to carry based on IP data, voice and video business. It for less transformation cost and the original bill of one-way cable TV network transformed into a two-way, can bear a variety of business two-way broadband network. The EoC technology has good adaptability and
flexible network scheme, make full use of the radio and television original coaxial access network resources, saving the door part of the line investment.
Will EPON technology and EoC technologies, unified net, made up of the whole solution, can radio fusion of three nets NGB provide access network of the best technology. EPON + EoC can provide data, video, voice in one of the three broadcast the overall carrying, through a access network for the past more than one the function of network The scheme in the development process of fully considering China's national conditions and the actual situation of the radio and television networks, in local nets level using the Cable network has wide power grid as a transmission medium, saving a lot of integrated wiring cost and operation and maintenance investment, with the high performance and low cost. EPON + EoC technology meets the digital TV broadcasting the two-way transformation and the needs of the national three nets fusion, NGB will promote the further development of industry in China, is an NGB cable operators network access layer preferred technology.
3 EPON EoC and network technology
3.1 EPON technology
Optical fiber transmission as a high rate, high capacity, many of the best media business, have already been backbone in man and a wide range of applications, in the access network level, optical fiber has also got the popularization and application. Optical fiber has long life, high reliability, robust of the advantages of the optical transmission < /list/cpzt_gldl.shtml > has strong ability to expand the bandwidth, and easy to realize the integration of various business platform.
EPON technology is passive optical network of Ethernet and combination of technology, according to the international standard IEEE802.3 ah can support 1.25 Gbit/s symmetric rate. As an important solution of optical fiber access network, EPON technology has ADSL, LAN and incomparable characteristic, also than APON,
BPON, GPON technology more efficient to meet the "EverythingoverIP" business needs more access. EPON access network has investment low cost, simple operation and maintenance the advantage for operators to solve the "last mile" problem provides a very economic effective broadband access solutions. At present, the technology at home and abroad have EPON got the large-scale application, obtains the domestic and foreign operators and manufacturers support and acceptance.
Through the EPON system equipment, use of optical fiber network cover/FTTB FTTH family, the enterprise users can provide maximum bandwidth of 1 Gbit/s transmission rate. Operators can use economic cost of investment and few fiber optic cable line, realized high-speed Internet access, IPTV < /list/wlds.shtml > multicast/demand high bandwidth IP data service delivery.
EPON system mainly by the OLT (OpticalLineTerminal, fiber optic lines terminal) and ONU (OpticalNetworkUnit, optical fiber network units) and separator (Splitter), which provide to IP OLT man, IPTV bearing network, NGN soft switching uplink interface. According to the end user of the business needs of different, operators can choose freely ONU terminal equipment to meet FTTH/FTTB/FTTC/FTTC + EoC and so on many kinds of application scenarios. The typical EPON network schemes shown as show in figure 1.
Fig attached-1 EPON typical network scheme
3.2 EoC technology
It is to point to in the EoC coaxial cables transmission Ethernet data of the technology. The way the EoC system, terminals, coaxial FenPeiWang components. The head of general on light node location, the distribution of upper Ethernet data, gathering terminal equipment role; Terminal on the home user's computer user access or interactive set-top box; Coaxial cable television network distribution from light to users of the position node home network, in addition to coaxial cable, but also including active amplifier, EoC jump by machine, branch/distributor equipments.
Now commonly used EoC head end equipment is based on HomePlugA V technology of active modulation access convergence equipment and its main function is to data baseband signal to OFDM way to 7 ~ 30 MHz modulation frequency band, again with the cable TV network in the mixed signals in catv HFC network coaxial cables transmission. Commonly used EoC client equipment is based on HomePlugA V technology users demodulation equipment, its main function is to all kinds of user terminal equipment computer, set-top box, IP telephone, etc, and access to the EoC system, and achieving with coaxial cable as medium two-way broadband access.
According to the cable operators EPON and EoC technology, OLT placed in the front of the network system, ONU placed in the floor, connecting EoC (EthernetoverCable) bureau end equipment, through HFC door. The user through cable TV coaxial cable transmit and receive data signal, and do not affect the cable TV signal transmission and reception. The biggest EoC host up to 80 M above the bandwidth, at most, can bring 64 from machine, more from sharing host machine bandwidth. The host in connection a certain number of cases from machine, from the bandwidth of the machine can be automatically adjusted, with QoS can be set of bandwidth from machine, the host can on SNMP network management. A bridge can extend cable TV signal transmission distance, jumper various cable TV signal amplifiers, realize two-way transmission of data, and achieved the data signals and TV signal transmission line.
At present the EoC mainstream product HomePlugA V/BPL technology, EoC head end equipment for cable bridge switches, cable bridge switches is coaxial data networks on cable television in the one-way amplifier jumper equipment, it will be the mixed signals through the frequency of segmentation method, the data signals don't through amplifier, cable TV signal after enlargement through the jumper again and data signals is mixed.
Cable bridge switches modular design, the main module has CATV module, ONU module, EoC head end module, exchange control module. These modules are as optional module configuration in the corresponding case. One master control module in ports exchange only cable bridge switches to be used. Modular design of the benefit that can be more flexible cable operators to meet the needs of different periods and the expansion of the flexible, maximize reduce investment cost, earn higher returns.
Different regions of the operators can according to economic development conditions, the user density, coverage, KaiTongLv and user bandwidth demand, the choose and buy different interface number of cable bridge switches, installations can choose indoor or outdoor. The user terminal equipment according to the number of network interface the main points of the interface, double interface and single four
network interface. The EoC head can need according to the number of module configuration, each module TV signal input and provide all the way all the Cable frequency mixing mouth, can simultaneously transmit and receive data signals and Cable TV signal mixed signals. CATV access module support single CATV take entrance, provide all the way the cable TV interface, transmission cable television signals.
The Lord by coupler may support more under way even coaxial channel. Using the high performance optical devices, spectral than for knowing the cover up to 20 km distance when, than for all four was covered up to 10 km distance. For all 4 when spectrometer than average bandwidth up to 15 Mbit/s, meet the user's bandwidth needs.
3.3 EPON + EoC networking applications
The EoC technology on traditional EPON and cable TV network technical reform, can use EPON equipment to finish the main lines of fiber optic cable transformation, the two-way user coaxial cable access network two-way transformation, using active EoC in networking, in the active ONU EoC head end, to cover all the users under light node, the performance requirements of users use have EoC client access. This will GuangBoShi one-way transmission network construction as the two-way transmission network.
EPON + EoC the typical application of network scheme as shown in figure 2 shows, cable bridge switches placed in the corridor or outdoor, covering a building or a unit. Now the network has laid light node, cable bridge switches don't configuration CATV module, through the radio frequency cable access to cable bridge switches, ONU module configuration in cable bridge switches, realize data or interactive television signal of the opponents.
Figure attached-2 EPON + EOC application network scheme
If now nets caused by the receiver down, cable bridge switches need integrated light receives function. Then cable bridge to switch configuration CATV module, through the optical fiber cable TV signal will access to bridge switches. ONU module configuration in cable bridge switches, realize data or interactive television signal of the opponents. Another thing, if now nets have laid light node, ONU placed on the floor, access the cable bridge several single port switches, the data signals through the cable access to cable bridge switches, realize data or interactive television signal back TV signal through the radio frequency cable access to cable bridge switches.
4 last word
The cable operators EPON EoC and comprehensive utilization technology which network resources, done quickly NGB access layer, the construction of the digital two-way transformation, reduce a lot of repetitions construction, saving building and operation and maintenance costs. Using EPON + EoC scheme, users need to indoor
wiring do any change, need to increase CNU terminal equipment can realize two-way, interactive, multi-function, many business, enjoy 3 nets fusion bring rich content. EPON + EoC scheme can improve the cable TV network technology level and business carrying capacity, play cable network wide frequency band, low cost, easy popularity of advantage, the number of cable television has become to thousands of multimedia information platform.
Two-way after the transformation of the cable TV network is bearing, offer three nets fusion business the most important network, will become the modern social activities in the most important information communications infrastructure. Wide power grid after two-way transformation, by using optical fiber and coaxial cable access styles for every family users can expand broadband access, can meet the standard high-definition TV programs and bandwidth demand, the user to appreciate the picture quality will be more sharp li lifelike, image is more clear. Through the article the "highway" users can quickly and easily handle information, transparence service information society and convenient service.。