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 transmiss


整個(gè)電信網(wǎng)按網(wǎng)絡(luò)功能分為三個(gè)部分：傳輸網(wǎng)、交換網(wǎng)和接入網(wǎng)。接入網(wǎng)負(fù)責(zé)將電信業(yè)務(wù)透明傳送到用戶(hù)，具體而言，接入即為本地交換機(jī)與用戶(hù)之間的連接部分，通常包括用戶(hù)線傳輸系統(tǒng)、復(fù)用設(shè)備、交叉連接設(shè)備或用戶(hù)/網(wǎng)絡(luò)終端設(shè)備。而實(shí)際上接供業(yè)務(wù)的實(shí)體就是業(yè)務(wù)結(jié)點(diǎn)。
一． 接入網(wǎng)的發(fā)展歷程
1. 接入網(wǎng)（AN：Access Network）是指由業(yè)務(wù)節(jié)點(diǎn)接口（SNI）和相關(guān)用
網(wǎng)絡(luò)接口（UNI）之間的一系列傳送實(shí)體（諸如線路設(shè)施和傳輸設(shè)施）所組成的為傳送電信業(yè)務(wù)提供所需傳送承載能力的實(shí)施系統(tǒng)，可經(jīng)由Q3管理接口進(jìn)行配置和管理。接入網(wǎng)可以被看作是與業(yè)務(wù)和應(yīng)用無(wú)關(guān)的傳送網(wǎng)，主要完成交叉連接、復(fù)用和傳輸功能，對(duì)用戶(hù)信令來(lái)說(shuō)是透明的?；诂F(xiàn)代電信網(wǎng)的接入網(wǎng)是綜合業(yè)務(wù)接入網(wǎng)，簡(jiǎn)單的本地話(huà)音接入將越來(lái)越不能滿(mǎn)足需要，語(yǔ)音、數(shù)據(jù)、圖像的綜合接入正成為接入網(wǎng)的發(fā)展趨勢(shì)。經(jīng)過(guò)多年的發(fā)展，接入網(wǎng)的界定雖然沒(méi)有變，但其內(nèi)涵和形式發(fā)生了很大的變化。性能明顯優(yōu)于傳統(tǒng)接入網(wǎng)的綜合光纖接入網(wǎng)將是用戶(hù)接入網(wǎng)今后的發(fā)展趨勢(shì)。光纖接入網(wǎng)是指從SNI到UNI全部或者部分采用光纖作為媒質(zhì)的接入網(wǎng)。ITU-T關(guān)于光纖接入網(wǎng)的建議指出，用戶(hù)接入系統(tǒng)由三部分組成：局端設(shè)備（OLT）、光分配網(wǎng)絡(luò)（ODN）和光網(wǎng)絡(luò)單元（ONU）。