摘要
虽然ADSL已成为当前的主流宽带接入技术，但如果要提供高清晰度或交互式视频业务，ADSL将无能为力。而光纤接人的带宽潜力是其它接入方式无法媲拟的，在接人网环境中用光纤取代铜缆可带来一系列的好处：消除电信网的瓶颈、降低维护费用、易于实现业务融合和提供新业务、提高信息传输质量和通信可靠性、方便系统未来扩容、节省建设投资等等。各大运营商都非常重视光纤接入网的建设，如北京网通（原北京电信）早在90年代末期就在北京地区新建了100多个用户光缆环，这100多个光缆环覆盖了北京大部分地区，在北京地区基本实现了光纤到大楼或小区（FTTB／FTTC）。虽然光纤到户（FTTH）是宽带接人的根本解决手段，但现阶段大规模实现FTTH还不经济可行，现阶段主要是实现FTTB／FTTC。对于FTTB／FTTC，可采用的传送技术手段目前以有源光纤接人（包括PDH、ATM、sDH、GE／FE等）为主，但无源光纤接入（PON）由于其良好的性能开始得到应用。而对于FTTH，PON则是最经济有效的技术手段。
Although ADSL has become current mainstream broadband access technology, but if high-definition or interactive video services are demanded, ADSL will be helpless. While the bandwidth potential of optical fiber access is unreachable by other access modes, optical fiber could bring a series of benefits by replacing copper cable in access network environment： eliminate bottleneck of telecom networks, reduce maintenance cost, easy to realize business convergence and provide new services, improve information quality and communication reliability, convenient for system expansion in the future, save construction investment etc. All major operators are concerned with construction of optical fiber access networks, e.g. Beijing CNC （former Beijing Telecom） had built over 100 user optical fiber rings in Beijing as early as late 90s, this 100 odd optical fiber rings cover most of Beijing, and have basically realized fiber-to-building or community （FTTB/FTTC） in Beijing area. Although fiber-to-home （FTTH） is the fundamental solution for broadband access, but it＇s not economical to realize FTTH in large scale at present stage, while FTTB/FTTC is the main task for the present stage. As for FTTB/ FTTC, currently adoptable transmission technical means are mainly dominated by active optical fiber access （including PDH, ATM, SDH, GE/FE etc.）, but passive optical fiber access （PON） has gradually got applicationdue to its good performance. For FTTH, PON will be the most economic and efficient technical means.
