With the development of communication, the information required to be transmitted is not only voice, but also text, data, images, and video. Coupled with the development of digital communication and computer technology, in the 1970s and 1980s, T1 (DS1)/E1 carrier systems (1.544/2.048Mbps), X.25 frame relay, ISDN (Integrated Services Digital Network) and FDDI ( Optical fiber distributed data interface) and other network technologies. With the advent of the information society, people hope that modern information transmission networks can provide various circuits and services quickly, economically, and effectively. However, due to the monotonicity of their services, the complexity of expansion, and the limitation of bandwidth, the above-mentioned network technologies are only in the original Modifications or improvements within the framework are no longer helpful.SDH was developed under this background. Among various broadband optical fiber access network technologies, the access network system using SDH technology is the most widely used.   The birth of SDH solves the problem of being unable to keep up with the development of the backbone network and user service requirements due to the bandwidth limitation of the inbound media, and the problem of the access “bottleneck” between the user and the core network, and at the same time, it has increased a large amount of bandwidth on the transmission network. Utilization rate. Since the introduction of SDH technology in the 1990s, it has been a mature and standard technology. It is widely used in backbone networks and the price is getting lower and lower. The application of SDH technology in the access network can reduce the huge bandwidth in the core network. Advantages and technical advantages are brought into the field of access networks, making full use of SDH synchronous multiplexing, standardized optical interfaces, powerful network management capabilities, flexible network topology capabilities and high reliability to bring benefits, and long-term benefits in the construction and development of access networks .