Optical fiber access network technology

The entire telecommunication network according to network function is divided into three sections: switching, transmission,and access. Access to telecommunications business transparent to users, transmit specific, access to local switch and the user that the connection between the parts, usually include subscriber line transmission system, reuse equipment, crossing connection device or user/network terminal equipment. And actually pick for business entity is business nodes.

1. Access network development process

1.1 Access Network (AN: Access by business) refers to a node interface (SNI)

and related users Network interface (UNI) between a series of transmit entity (such as line facilities and transmission facilities) for transmission consisting of

telecommunication business provide the required transmit load capacity,

implementation system configurations percentile management interface via and management. Access can be seen as with business and application irrelevant

transmission network, mainly finish crossing connection, reuse and transmission function, it is transparent to users of signaling.

Based on modern of telecommunication network access network is integrated service access, simple local voice access will be increasingly cannot meet the requirements, the voice, data and image comprehensive access is becoming access network

development trend. After years of development, access network define though does not change, but its connotation and forms has changed significantly. Superior

traditional access network integrated optical fiber access network will be users access the future developing trend.

Optical fiber access from SNI to UNI refers to all or part of the access network by using optical fiber as medium. ITU - T about access network recommendations indicate that fiber, user access system is composed of three parts: optical line

terminal(OLT), optical distribution network (ODN) and optical network unit (ONU).

1.2According to the requirement of system access framework and the important characteristics, access network can be summarized as the following:

1.2.1 Access to access business provides bearing capacity, achieve business

transparent transfer.

1.2.2. The access is transparent to users signaling, except for some users signaling format conversion outside, signaling and business processing function is still in business node.

1.2.3 The introduction of should not be restricted access all kinds of existing access types and business, access network should through the limited standardization

interface and business node connected.

1.2.4Access network have independent from the business node in the network

management system, this system through the standardized interfaces connected TMN, access network operation for implementation TMN, maintenance and management. 2 .fiber structure

2.1general linear structure. Refer to the public bus, fiber as each user terminals

through direct connect with bus coupler network structure. Its characteristic is sharing backbone fiber, save lines to remove node investment, the demand is higher, dynamic range, interfere with each other effect is small. Defect is loss of accumulation, the backbone fiber user acceptance dependence is strong.

2.2 ring structure. Refers to all share a fiber optic link node, fiber optic link its end to end the closed loop network structure. Characteristic is self-healing, namely can be realized without intervention, the network can be in a relatively short period of time to recover from failure have preached business, high reliability. Defect is hanged by the number of users of monocylic limited, polycyclic interchange is relatively complex, not suitable for CATV, etc FenPeiXing business.

2.3star structure. This structure is actually point-to-point way, each user terminals in the central node through with control and switch functions of the astral couplers exchange information. Characteristics of simple structure, maintenance is convenient

and easy to upgrade and expansion between, each user relatively independent, good secrecy, business adaptability. Defect is higher, networking required fiber cost of poor flexibility, high reliability requirements of central node.

2.4 tree structure. Similar to the branches, a hierarchical structure, shape in transfer boxes and FenXianHe place adopts multiple optical distributor, will signal filtering down top end innings allocation, have strong control coordination. Characteristic is suitable for broadcasting business. Defect is power loss is bigger, two-way

communication difficulty bigger.

3．The status of optical access network in the modern communication

Optical fiber in realizing national information modernization access plays a more and more important role, is an indispensable part of modern communications network. Modern communications network basic realized based on fiber backbone transmission and exchange, and access section is still restricted modern telecommunications further development and improvement of the "bottleneck", therefore, to construction of national information infrastructure (NII), access network is the key. Access network technology development, will result in great changes of telecommunications and information network, namely, voice, data, video, etc. Various kinds of information transmission, comprehensive business together for implementing the resources

sharing, and gradually optimized communication network, greatly improving network benefits.

Two optical fiber optical transmission technology access with the combination of the access technology

3.1 Light transmission technology development and evolution

Since 1979, the human use of optical fiber as communication mode, optical

transmission technology experience since from analog to digital, from PDH to

sdh-based WDM, from passive and active to a series of MSTP from SDH to the development and evolution process, transmission capacity and reliability, the

transmission distance such indicators have reached a very high level.

The current mainstream of optical transmission technology is still SDH, STM - 1/4/16/64/256 series synchronous transfer module has been achieved, including STM - 256 frame rate as high as 40Gbps. Based on SDH, fusion broadband data business multi-task transmitting platform (the MSTP) has also become the best choice for today's construction intracity networks, moreover elastic grouping ring (RPR)

technology is also gradually become the direction of the development of a light transmission. The future will be optical transmission network to optical transmission network (otns) in the direction of development, many exchange, network otns choose road and other intelligent function will be implemented on light layer. Otns the

intelligent network development degree can realize ASON intelligent optical network.

3.2 Light transmission technology and access technology constitute fiber access network

The needs of the user, the diversification and broadband access technology from initial made of pure narrowband access to broadband access, size, and with integrated access to transmission platform requirement light more and more is also high. Optical transmission technology and access technology together constitute fiber access network system. Optical fiber access network in different stages of

development of need to resort to the corresponding optical transmission means to achieve the operational load and transfer. With the light network will be dispersed access devices (OLT ONU) together with organic whole, form a unified fiber access network system.

4. The current development of fiber-optic access hotspot

Currently, fiber-optic access network continue presented the vigorous

development momentum and various new access technology arises at the historic moment. The development of better have xDSL, FTTX, dual bus size take

comprehensive access technologies. In addition, HFC APON EPON, such technology is also in constant developing and perfecting.

4.1 The development and application of XDSL

XDSL technology refers to the ADSL (asymmetric digital subscriber loop) as a representative of digital subscriber loop (DSL) the floorboard of a series of

technology.

By using of ground wire although more than 2Mbps broadband data transmission, but the transmission distance is very limited. XDSL and optical fiber integrated access network structure, with the UNI bounded user-oriented provide narrowband normal telephone, 2Mbps line, 10Base_T and ATM broadband interface. Using fibre solve access network transmission of feeder section, XDSL solve finally hundreds meters to

3.5 kilometers (in this range, can guarantee a high rate), it is quite broadband access broadband technology effectively. The current market most successful is ADSL technologies, including China telecom, China netcom, China unicom, China tietong, each big telecom operators are spending heavily construction ADSL network. In the user is relatively scattered, twisted-pair cable resources under the condition of

comparative energetic, ADSL can low cost to solve users network bandwidth needs. SHDSL, HDSL can provide users with broadband data line, these two kinds of digital subscriber loop in special circumstances, the technical solution to the problem of providing data line.

VDSL technology is with ADSL) the development and popularization of and

gradually moving towards the commercial, but because it can support distance is short, at present its popularity still far less ADSL.

4.2 FTTX technology

In all sorts of broadband access network technology, optical SDH technology adopted the access network system is applied the most common. SDH technology application in access network has already widespread, but still just FTTC (optical fiber to the side of the road), FTTB (fiber to the floor), the huge bandwidth optical fiber level still no to household. Therefore, to really provide broadband business ability, just using SDH technology solve feeder, wiring, paragraph of the broadband is not enough, still need to introduce line in part by broadband access technology combined. Can FTTB/C + used respectively FTTB/C + xDSL, Cable Modem, FTTB/C + local-area network (LAN) access methods such as resident and company respectively, enterprise users to

provide business. Among them the way FTTX + LAN FTTLAN is called again, in this way our Shanghai, Beijing and other developed city new district has been widely used. The final is FTTH access development goals, but because the cost, the user needs and market and other reasons, FTTH is still a long-term task.

Access the latest development direction with SDH support for IP business is, is to develop a business network platform for MSTP/RPR) (. FTTX MSTP/RPR and combining with business realized width comprehensive transfer.

4.3Double (more) bus size take integrated business access network

Optical fiber access from the preliminary narrowband integrated service access to comprehensive business access with width of the development process, had two ideas: a view by unified IP business platform realize voice and data services integrated access; Another argument is because Everything over IP technology in be used

actually are still exist many problems, when in to realize comprehensive access or let narrowband service (circuit switching methods) and broadband business (packet switching mode) respectively take different channels. The former realization ways can the soft exchange to do help, then a realization way by current is most mainstream solutions -- double (more) bus integrated service access network.

In 1999, he launched a double before and after the comprehensive access network equipment bus model. Some manufacturers provide bus types according to the

backboard, and puts forward four buses parlance, including: management bus, TDM business bus, group business bus, general bus. General bus is to expand business ability, or to support now still unforeseeable some business and reserved. Due to its specific also unable to estimate the design parameters usually be categorized as one of the first three bus. Management bus is to realize the management of the whole system is designed for the Lord, because the bus ability to support business types is more and more abundant, need management information more and more, now also many USES high-speed management bus bus. This so-called "dual bus", is providing the

equipment backplane of the two businesses bus, namely TDM bus and packet bus. Most of the developed countries access equipment is dual bus structure. International technical development direction, adopt the most advanced system structure, launched

with IP for the kernel, built-in MSTP double bus type comprehensive access network equipment. Can foresee dual bus integrated access network is the development

direction of access in the coming years, each big access network equipment

manufacturers will strive for in this huge market competitive advantage, to

re-establish throughout the status of optical fiber access product market.

5. Access network support business

5.1 Voice class business: SPC telephone new business, magnetic card phone business, etc

5.2Data class business: DDN business, packet switching, etc

5.3 Image communication class business: meeting TV business, videophone business, etc

5.4 Multimedia business: home office, shopping, VOD, remote medical treatment, etc

6.the development direction of future optical fiber access

6.1 Broadband is changed and comprehensivized

Broadband access is market development trends, fiber in-home will be broadband access inevitable. XDSL, dual bus integrated access as the transition complete fibre optic access technology, will play in the next few years broadband market protagonist. Future access to achieve a single platform with various business width of

comprehensive access, achieve business and network of separation, i.e. to further to be changed to the broadband and integrated direction. Meanwhile fiber access

network also must be able to support and other access flexible joint networking.

6.2 To next generation network (NGN) of evolution

Judging from the technical development, the traditional telephone network, data communications network and the technology of industry of cable television network three is gradually disappear, technology difference of fusion will further trigger network fusing, business fusion and industrial integration. Next generation network (NGN) are available including voice, data and multimedia and other business

integrated, open network. The trend of its development can be summarized as:

network equipment of components, network communication gateway change, access technology diversification, network management integration, terminal intelligent, business exchange control functions of separation and core network group.

In the future of communications-net NGN dominant, optical fiber access network will also after fusion to next generation network with them. Optical fiber access should be a continuous development, continuously innovative open system, access network equipment can through the corresponding signaling gateway and relay gateway will narrowband service access to NGN network, through the broadband data gateway will broadband access to NGN network. With the telecommunications industry monopoly market disappear and telecommunications business market opening, telecom business functions, access technology unceasing enhancement, access is also associated with development, mainly displays in the following:

6.2.1 The complexity of the access is increasing. Different access technology with comprehensive competition between use, and require the support of large quantities of telecom business such as the complexity of that access network increases.

6.2.2 Access to expand in the scope of the services. Along with the development of communication technology and communications network, a local exchange capacity is expanding constantly, exchange, in decreasing number of small local in capacity, convert hubs and multiplex etc, it makes access network service scope expands unceasingly.

6.2.3 The standardization level access is increasing day by day. In a local exchange gradually V5. Based on the open after X standard interface, telecom operators more freely choose to access network technology and equipment.

6.2.4 Access network should support a higher-level business. The development of market economy, prompting commercial and corporate clients demand for greater capacity for the access lines, especially LAN interconnection data applications, demand reliability, short time limit of connection. Along with the optical fiber

technology to users of the outspread, CATV network development to the user loop development brings opportunities.

6.2.5 Support technology more diverse. Access Although currently in access the content of the optical transmission in growing, but how to make better use of the existing twisted-pair cable will be taken into account, but to demand rapid

construction of large capacity access lines, it can choose wireless link.

6.2.6 Optical fiber technology will more applied to access. As fiber-optic coverage expansion, optical fiber technology will also increasingly used to access network, from development to the perspective, SDH, ATM, IP/DWDM currently only applies to trunk cable segment and digital transmitter interface, with the bureau of business development, fiber interface will further expand to the roadside, and finally into the home, truly realize broadband fiber access, realize unified broadband network

structure, therefore, light will really become the telecommunications network

information superhighway solid network foundation.

光纤接入网技术

整个电信网按网络功能分为三个部分：传输网、交换网和接入网。接入网负责将电信业务透明传送到用户，具体而言，接入即为本地交换机与用户之间的连接部分，通常包括用户线传输系统、复用设备、交叉连接设备或用户/网络终端设备。而实际上接供业务的实体就是业务结点。

一． 接入网的发展历程

1. 接入网（AN：Access Network）是指由业务节点接口（SNI）和相关用 网络接口（UNI）之间的一系列传送实体（诸如线路设施和传输设施）所组成的为传送电信业务提供所需传送承载能力的实施系统，可经由Q3管理接口进行配置和管理。接入网可以被看作是与业务和应用无关的传送网，主要完成交叉连接、复用和传输功能，对用户信令来说是透明的。基于现代电信网的接入网是综合业务接入网，简单的本地话音接入将越来越不能满足需要，语音、数据、图像的综合接入正成为接入网的发展趋势。经过多年的发展，接入网的界定虽然没有变，但其内涵和形式发生了很大的变化。性能明显优于传统接入网的综合光纤接入网将是用户接入网今后的发展趋势。光纤接入网是指从SNI到UNI全部或者部分采用光纤作为媒质的接入网。ITU-T关于光纤接入网的建议指出，用户接入系统由三部分组成：局端设备（OLT）、光分配网络（ODN）和光网络单元（ONU）。

2. 根据接入网框架和体制要求，接入网的重要特征可以归纳为如下几点：

（1）．接入网对于所接入的业务提供承载能力，实现业务的透明传送。

（2）．接入网对用户信令是透明的，除了一些用户信令格式转换外，信令和业务处理的功能依然在业务节点中。

（3）．接入网的引入不应限制现有的各种接入类型和业务，接入网应通过有限的标准化的接口与业务节点相连。

（4）．接入网有独立于业务节点的网络管理系统，该系统通过标准化的接口连接TMN，TMN实施对接入网的操作、维护和管理。

二．光纤的结构

1.总线形结构。指以光纤作为公共总线、各用户终端通过耦合器与总线直接连接的网络结构。其特点是共享主干光纤，节约线路投资，增删节点容易，动态范围要求较高，彼此干扰效小。缺点是损耗积累，用户接受对主干光纤的依赖性强。

2.环形结构。指所有节点共用一条光纤链路，光纤链路首尾相连自成封闭回路的网络结构。特点是可实现自愈，即无需外界干预，网络可在较短的时间自动从失效故障中恢复所传业务，可靠性高。缺点是单环所挂用户数量有限，多环互通较为复杂，不适合CATV等分配型业务。

3.星形结构。这种结构实际上是点对点方式，各用户终端通过位于中央节点具有控制和交换功能的星形耦合器进行信息交换。特点是结构简单，使用维护方便，易于升级和扩容，各用户之间相对独立，保密性好，业务适应性强。缺点是所需光纤代价较高，组网灵活性较差，对中央节点的可靠性要求极高。

4.树形结构。类似于树枝形状，呈分级结构，在交接箱和分线盒处采用多个分路器，将信号逐级向下分配，最高级的端局具有很强的控制协调能力。特点是适用于广播业务。缺点是功率损耗较大，双向通信难度较大。

三．光纤接入网在现代通信网中的地位

光纤接入网在实现国家信息现代化过程中起着越来越重要的作用，是现代通信网不可或缺的组成部分。现代通信网基本实现了基于光纤的骨干网的传输和交换，而接入段仍然是制约现代电信网进一步发展和完善的“瓶颈”，因此，要建设国家信息基础结构（NII），接入网是关键。接入网技术的发展，将导致通信信息网的巨大变化，即语音、数据、图像等各种信息业务综合一起传送，实现资源共享，逐步优化通信网络，大大提高网络效益。光纤接入网是光传输技术与接入技术相结合的产物

1．光传输技术的发展和演进

自从1979年人类使用光纤作为通信方式以来，光传输技术经历了从模拟到数字、从PDH到SDH/WDM、从有源到无源、从SDH到MSTP的一系列发展和演进过程，传输容量、可靠性、传输距离等指标都已经达到了相当高的水平。

当前主流的光传输技术仍然是SDH，STM-1/4/16/64/256系列同步转移模块都已经实现，其中STM-256帧速率高达40Gbps。基于SDH、融合宽带数据业务的多业务传送平台（MSTP）也已经成为当今建设城域网的最佳选择，此外弹性分组环（RPR）技术也逐步成为光传输发展的一个方向。未来光传输网络将向光传送网（OTN）的方向发展，在OTN网络中很多交换、选路和其它智能化功能将在光层上实现。OTN网络的智能化发展到一定程度就可实现智能光网络（ASON）。

2．光传输技术与接入技术共同构成光纤接入网

用户需求的多样化和宽带化使得接入技术从最初的纯窄带接入发展到宽带接入、宽窄带综合接入，因而对于光传输平台的要求也越来越高。

光传输技术与接入技术融合在一起即构成光纤接入网系统。光纤接入网在不同的发展阶段需要借助于相应的光传输手段来实现业务的承载和传送。借助于光网络将分散的接入设备（OLT和ONU）连成有机的整体，形成统一的光纤接入网系统。

四． 当前光纤接入网的发展热点

当前，光纤接入网继续呈现出蓬勃发展的势头，各种新的接入技术应运而生。其中发展较好的有xDSL、FTTX、双总线宽窄带综合接入等技术。此外EPON、APON、HFC等技术也在不断发展和完善。

1. XDSL的发展和应用

XDSL技术是指以ADSL（不对称数字用户环路）为代表的数字用户环路（DSL）的一系列技术的总称。利用双绞铜线虽然可传输2Mbps以上的宽带数据，但是传输距离十分有限。XDSL与光纤配合的综合接入网结构，在UNI界面向用户提供窄带普通电话、2Mbps专线、10Base_T和ATM宽带接口。利用光纤解决接入网馈线段的传输，XDSL解决最后几百米到3.5公里（在此距离内，可以保证较高速率）的宽带接入，是相当有效的宽带接入技术。目前在市场上最

为成功的是ADSL技术，包括中国电信、中国网通、中国联通、中国铁通在内的各大电信运营商都投入巨资建设ADSL网络。在用户相对比较分散、双绞线资源比较充沛的情况下，ADSL可以低成本地解决用户对网络带宽的需求。SHDSL、HDSL可以为用户提供宽带数据专线，这两种数字用户环路技术解决了在特殊情况提供数据专线的难题。

VDSL技术是随着ADSL的发展和普及而逐步走向商用的，但是由于它能够支持的距离较短，目前它的普及程度还远不及ADSL。

2．FTTX技术

在各种宽带光纤接入网技术中，采用了SDH技术的接入网系统是应用最普遍的。SDH技术在接入网中的应用虽然已经很普遍，但仍只是FTTC（光纤到路边）、FTTB（光纤到楼）的程度，光纤的巨大带宽仍然没有到户。因此，要真正向用户提供宽带业务能力，单单采用SDH技术解决馈线、配线段的宽带化是不够的，在引入线部分仍需结合采用宽带接入技术。可分别采用FTTB/C＋xDSL、FTTB/C＋Cable Modem、FTTB/C＋局域网（LAN）接入等方式分别为居民用户和公司、企业用户提供业务。其中FTTX+LAN的方式又被称为

FTTLAN，这种方式在我国上海、北京等发达城市的新建小区已经被广泛应用。FTTH是接入网的最终发展目标，但由于成本、用户需求和市场等方面的原因，FTTH仍然是一个长期的任务。

接入网用SDH的最新发展方向是对IP业务的支持，即发展为多业务传送平台（MSTP/RPR）。MSTP/RPR与FTTX相结合实现了宽窄带业务的综合传送。

3．双（多）总线宽窄带一体化综合业务接入网

光纤接入网从初步的窄带综合业务接入向宽窄带综合业务接入发展的过程中，有过两种观点：一种观点认为借助于统一的IP业务平台实现语音和数据业务的综合接入；另一种观点认为由于Everything over IP的技术在实际使用中还存在诸多问题，在实现综合接入时还是让窄带业务（电路交换方式）和宽带业务（分组交换方式）分别走不同的通道。前一种实现方式可以借助于软交换来做，而后一种实现方式则借助于目前最为主流的解决方案——双（多）总线综合业务接入网。

在1999年前后，就推出了双总线模式的综合接入网设备。有些厂家根据背板提供的总线种类，提出了四总线的说法，包括：管理总线、TDM业务总线、分组业务总线、通用总线。通用总线是为了扩充业务的能力，或是为了支持现在还无法预见的某种业务而预留的。由于还无法估计其具体的设计参数，一般将其归为前三种总线中的一种。管理总线是为了实现整个系统的管理而设计的具有主备能力的总线，由于支持的业务种类越来越丰富，所需要的管理信息也越来越多，现在管理总线也多采用高速总线。这里所谓的“双总线”，就是在设备背板上提供的两种业务总线，即TDM总线和分组总线。

发达国家的接入网设备大多是双总线结构。国际的技术发展方向，采用了最先进的体系结构，推出了以IP为内核、内置MSTP的双总线式综合接入网设备。可以预见双总线综合接入网是接入网未来几年的发展方向，各大接入网设备制造商将努力争取在这个巨大市场上的竞争优势，来重新确立在整个光纤接入产品市场中的地位。

五．接入网支持的业务

1. 话音类业务：程控电话新业务、磁卡电话业务等

2.数据类业务：DDN业务、分组交换业务等

3.图像通信类业务：会议电视业务、可视电话业务等

4.多媒体业务：居家办公、购物、VOD、远程医疗等

六． 未来光纤接入网的发展方向

1．宽带化和综合化

宽带接入是市场发展的总体趋势，光纤入户将是宽带接入的必然。xDSL、双总线综合接入等作为完全光纤接入的过渡技术，将在未来几年内扮演宽带接入市场的主角。未来的接入网要实现单一平台上宽窄带多种业务的综合接入，实现业务与网络的分离，即要进一步向宽带化和综合化的方向发展。同时光纤接入网也要能够灵活支持与其它接入方式的联合组网。

2．向下一代网络（NGN）的演进

从技术发展上来看，传统的电话网、数据通信网以及有线电视网三大行业的技术差别正在逐步消失，技术的融合将进一步引发网络融合、业务融合及产业融合。下一代网络（NGN）是可提供包括话音、数据和多媒体等业务的综合的、开放的网络。其发展趋势可概括为：网络设备构件化、网络互通网关化、接入技术多样化、网管一体化、终端智能化、业务交换控制功能分离和核心网络分组化。

NGN在未来通信网中占据主导地位后，光纤接入网也将随着融合到下一代网络当中。光纤接入网应该是一个不断发展、不断革新的开放体系，接入网设备可以通过相应的信令网关和中继网关将窄带业务接入到NGN网络中，通过宽带数据网关将宽带业务接入到NGN网络中。

随着电信行业垄断市场消失和电信网业务市场的开放，电信业务功能、接入技术的不断提高，接入网也伴随着发展，主要表现在以下几点：

（1）.接入网的复杂程度在不断增加。不同的接入技术间的竞争与综合使用，以及要求对大量电信业务的支持等，使得接入网的复杂程度增加。

（2）.接入网的服务范围在扩大。随着通信技术和通信网的发展，本地交换局的容量不断扩大，交换局的数量在日趋减少，在容量小的地方，改用集线器和复用器等，这使接入网的服务范围不断扩大。

（3）.接入网的标准化程度日益提高。在本地交换局逐步采用基于V5.X标

准的开放接口后，电信运营商更加自由地选择接入网技术及系统设备。

（4）.接入网应支持更高档次的业务。市场经济的发展，促使商业和公司客户要求更大容量的接入线路用于数据应用，特别是局域网互连，要求可靠性、短时限的连接。随着光纤技术向用户网的延伸，CATV的发展给用户环路发展带来了机遇。

（5）.支持接入网的技术更加多样化。尽管目前在接入网中光传输的含量在不断增加，但如何更好地利用现有的双绞线仍受重视，但对要求快速建设的大容量接入线路，则可选用无线链路。

（6）.光纤技术将更多的应用于接入网。随着光纤覆盖扩展，光纤技术也将日益增多地用于接入网，从发展的角度看，SDH、ATM、IP/DWDM目前仅适用于主干光缆段和数字局端机接口，随着业务的发展，光纤接口将进一步扩展到路

边，并最终进入家庭，真正实现宽带光纤接入，实现统一的宽带全光网络结构，因此，电信网络将真正成为本世纪信息高速公路的坚实网络基础。