What is the network structure of the Optical Access Network (OAN)
Optical access network (OAN) refers to the use of optical fiber as the main transmission medium to realize the information transmission function of the access network. It is connected to the service node through the optical line terminal (OLT), and connected to the user through the optical network unit (ONU). The optical fiber access network includes remote equipment-optical network unit and central office equipment-optical line terminal, which are connected by transmission equipment.The main components of the system are OLT and remote ONU.They complete the conversion of signaling protocols from the service node interface (SNI) to the user network interface (UNI) in the entire access network. The access device itself also has networking capabilities and can form various forms of network topology. At the same time, the access equipment also has the functions of local maintenance and remote centralized monitoring, forming a maintenance management network through transparent optical transmission, and bringing it into the network management center for unified management through the corresponding network management protocol.
The role of the OLT is to provide an interface between the access network and the local switch, and communicate with the optical network unit on the user side through optical transmission. It completely separates the switching function of the switch from user access. The optical line terminal provides maintenance and monitoring of itself and the user end. It can be directly placed at the exchange office end together with the local exchange, or it can be set at the remote end.
The function of ONU is to provide a user-side interface for the access network. It can be connected to a variety of user terminals, and at the same time has a photoelectric conversion function and corresponding maintenance and monitoring functions. The main function of the ONU is to terminate the optical fiber from the OLT, process the optical signal and provide service interfaces for multiple small businesses, business users and residential users. The network end of the ONU is an optical interface, and its user end is an electrical interface. Therefore, ONU has optical/electrical and electric/optical conversion functions. It also has the functions of digital/analog and analog/digital conversion of dialogue. The ONU is usually placed closer to the user, and its location has great flexibility.
Optical Access Network (OAN) is divided into Active Optical Network (AON, Active Optical Network) and Passive Optical Network (PON, Passive Optica Optical Network) in terms of system distribution.
The topological structure of the optical fiber access network refers to the geometric arrangement of transmission lines and nodes. It shows the mutual position and interconnection layout of each node in the network. The topological structure of the network has an important influence on the network function, cost and reliability. The three basic topological structures are: bus-shaped, ring-shaped and star-shaped. From this, bus-star, double-star, double-ring, bus-bus and other combined application forms can be derived. Each has its own characteristics and mutual supplement.