【正文】 laying fiber to the user munity。 laying fiber to the office。s main purpose is to provide video on demand (VOD) services. ADSL 6 Mbps bandwidth for each can transmit 2 sets of MPEGⅡ ~ 3 or 4 sets of MPEGI digital image signal. ADSL uses discrete multifrequency transmission coding and noncarrier amplitude modulation, phase modulation technique. From a technical point of view, it solves the switch to the user39。s virtual image, so traditional access technologies (access, access routing) for high performance requirements in order to break through the bottleneck of work access links. To increase the work bandwidth of the last paragraph in the distance, in a wide range of reach and satisfy the user in the home or small office munications requirements of the basic premise. The local loop bottleneck is provided by the lower bit rate today due, in fact, in addition to local loop bandwidth limitations, the current data work technology has been sufficient to ensure the provision of moving images, and other highbandwidth services. 3. Access Technology From the total consideration, access to technology can be divided into wired and wireless access technologies, access to two types, wired access technologies can be divided into copper and fiber access technology access technology types. copper access technology Copper access the main focus is to consider how the current munications work in the total transmission length of about 1 / 3 part of the user line. The current copper access technologies are: highspeed digital subscriber line (HDSL) technology, asymmetric digital subscriber line (ADSL) technology and high bitrate Digital Subscriber Line (VDSL) technology. HDSL system using 2B1Q line code type, use of echo cancellation, adaptive filtering, signal processing technology to solve a number of ordinary users in a pair of twoway 18 transmission of online information , two pairs of users of online transmission of information. HDSL has the advantage of full use of existing cables to achieve expansion, and can solve the small number of users to transmit and 2048 kbps 384kbps broadband signals. The disadvantage is that currently can not transmit information over 2048kbps, transmission distance is limited within 6 to 10 km. ADSL asymmetric key used to transmit interactive broadband services. And as HDSL, ADSL is also trying to improve the general subscriber line highfrequency transmission. The socalled asymmetric means that such systems upstream direction (from user terminals to send direction to the switch) and the downstream direction (from the switch to send the user terminal direction) rate of asymmetric information. The uplink direction can send 64kbps ~ 384kbps digital signal。s last mile work access part is the most promising part of a substantial increase in work performance. On the local loop 17 work this is a bottleneck on the 100 million users worldwide access lines, its function is limited to impede the development of business users, while the other end with subscriber line highperformance equipment in sharp contrast. As electronic technology and the rapid development of optoelectronic technology, digital electronic system (from a personal puter to a work switch or router) and information transmission equipment performance are in the fast and steady growth, as the bottleneck to solve this ring circuit provides a broad development prospects. As the copper local loop is still analog signal transmission, people are still using the narrow radio channels across the crowded radio spectrum. How to access the current bottleneck in largescale widening work of the world39。 wiring system may be cable and optical cable generally a few hundred meters in length。s silicon technology has been silicon film and processing technology 16 has bee mature, because silicon has the people39。我國的發(fā)展趨勢將可能跨越 APON、 BPON 和 EPON 階段，從寬帶點到點以太網(wǎng) 光纖系統(tǒng)和GEPON 開始，乃至較快地過渡到 GPON 階段。在此主要討論光纖通信的發(fā)展趨勢和市場。 筆者認為，光纖通信技術尚有很大的發(fā)展空間，今后會有很大的需求和市場。特別是光纖，國外對中國傾銷。 近來有人對光纖通信的發(fā)展情景有些困惑。 GPON 和EPON/GEPON 面臨的共同挑戰(zhàn)有：怎樣才能在 Ethemet/GFP 上有持久承載 TDM 業(yè) 13 務并能提供電信級的服務質量；其次，由于 GPON 和 EPON/GEPON 是點對多點的星形或樹形網(wǎng)絡，需要通過一個 1+1 并經(jīng)過不同路由的光網(wǎng)絡來實現(xiàn)電信級的保護恢復要求，網(wǎng)絡成本將非常高；第三，目前 GPON 和 EPON/GEPON 設備成本主要受限于突發(fā)光發(fā)送 /接收模塊以及核心的控制模塊 /芯片。但就傳輸效率而言，則 GPON 無論在擾碼效率、傳輸匯聚層效率、承載協(xié)議效率和業(yè)務 適配效率方面都是最高的，因此其總效率最高。可以幫助運營商完成從傳統(tǒng) TDM 語音電路向全 IP 網(wǎng)絡的平滑過渡，其缺點是依然保留有復雜的 ATM 層功能，成本偏高?？偟膩砜?， GPON 不是制造商驅動的技術標準，而是一種運營商驅動的標準，因此具有更周到 的運營利益考慮，速率更高，可達 ；具有通用的映射格式，可適應任何新老業(yè)務；具有豐富的 OAMamp。另一方面， GPON 采用了一些最新的技術成果，除了最重要的 GFP 封裝外，還包括前向糾錯等新技術。 從技術角度， GPON 是 BPON 的繼承和發(fā)展。而且， GPON 采用了兩種封裝方式，除了傳統(tǒng)的 ATM 外，還在傳輸匯聚 層采用了一個全新的基于 sDH 的標準通用組幀程序 GFP，這是一種可以透明地高效地將各種數(shù)據(jù)信號封裝進現(xiàn)有 SDH 網(wǎng)絡的通用標準信號適配映射技術，可以適應任何用戶信號格式和任何傳輸網(wǎng)絡制式，即可以按固有格式傳送語音、數(shù)據(jù)和視頻信號，無需附加 ATM 或 P 封裝層，全面體現(xiàn)了業(yè)務提供商對業(yè)務提供的靈活要求，而 APON/BPON 和 EPON/GEPON 對每種特定業(yè)務都需要提供特定的適配方法。 4. GPON 2020 年，在 IEEE 積極制定 EPON 標準的同時， FSAN 組織開始發(fā)起制定速率超過 1Gb/s 的 PON 網(wǎng)絡標準千兆以太網(wǎng)無源光網(wǎng)絡 (GPON)，隨后， ITUT 也介入了這一新標準的制定工作并于 2020 年 1 月通過兩個有關 GPON 的新的標準 和(速率提高到 )。前者是由于 12 采用 8B/10B 的線路編碼，引入 20%的帶寬損失，再加上其他開銷，可用負荷僅 50%左右，而 APON 和 GPON 都采用 NRZ 擾碼為線路碼，沒有帶寬損失。 IEEE 規(guī)范的 GEPON 技術的規(guī)范性好，上下行波長分別是 1310 和1490nm，上下行速率為 ，傳輸距離是 10/20km，分路比是 16，主要業(yè)務是數(shù)據(jù)和語聲， 增加一個 1550nm 電視廣播波長后，成為語聲、數(shù)據(jù)和電視三合一的“triple—play”寬帶業(yè)務捆綁服務，而這將是未來家庭業(yè)務的 “殺手锏應用 ”。而EPON/GEPOkI 的 ONU 上行比特流是輪流發(fā)送的突發(fā)數(shù)據(jù)包， OLT 的接收定時恢復、判決門限設置、測距和延時補償比較復雜。上行方向工作于 TDMA 方式，來自不同時隙的ONU 數(shù)據(jù)流匯聚到公共光纖設施和 OLT。 EPON/GEPON 與傳統(tǒng)點到點以太網(wǎng)主要不同處在于工作于點到多點通信方式。在實際中， EPON 和 GEPON 的基本差別就是標準化，前者往往指非標設備，后者指符合 ，規(guī)范的設備。 3. EPON/GEPON 隨著 IP 的崛起和發(fā)展，有人提出了 EPON 的概念，即在與 APON 和 BPON 類似的結構和 的基礎上 ，設法保留其精華部分 —物理層 PON；而以以太網(wǎng)代替 ATM作為鏈路層協(xié)議，構成一個可以提供更大帶寬、更低成本和更寬業(yè)務能力的新的結合體 EPON。按32 路計算，每一個分支的可用帶寬僅剩 ，再按 10 個用戶共享，則每個用戶僅能分得約 2Mb/s 的帶寬而已。最后，從長遠的業(yè)務發(fā)展趨勢看， APON 的可用帶寬仍然不夠。一個ATM 化的無源光網(wǎng)絡 (APON/BPON)可以利用 ATM 的集中和統(tǒng)計復用，再結合無源分路器對光纖和光線路終端的共享作用，使性能價格比有重要改進，目前在美國和日本等國已經(jīng)開始商用。另外，其樹型分支拓撲結構使用戶不具備保護功能或保護功能成本較高，影響了大規(guī)模發(fā)展。最后，考慮采用 PON 技術后比