GPON system consists of optical line terminal (OLT), optical network unit (ONU) and optical distribution network (ODN).
OLT is generally placed in the CO (central office) machine room, which is mainly used to gather the optical signals uploaded by ONU; ONU can be set in the corridor, the street and the user's home according to different access applications, providing users with various access interfaces (such as POTS interface of telephone service, GE/FE interface of Internet service, etc.); ODN is composed of optical fiber, one or several passive optical dividers and other passive optical devices, with which optical channels could be provided between OLT and ONU. OLT and ONU communicate through ODN.
In GPON fiber optic network, OLT is a king of service node side equipment of access network. It is connected to the corresponding service node equipment through SNI (service node interface) and complete the service access of access network. ONU is a king of user side equipment of the access network. It is connected to CPE (customer premises equipment) through UNI (user to network interface).
OLT is the core component of optical access network, which is equivalent to L2 exchanger or L3 router of traditional communication, and is also a multi-service platform. On the one hand, in order to transmit signals to the end user, it will gather the signals carrying various services at the central office and send them to the access network according to a certain signal format. On the other hand, it will send the signals from the end user to various service networks according to the service types.
With one OLT, multiple ONU can be connected through a splitter, and the control, management and ranging functions of ONU can be realized. OLT is like a commander, commanding these ONU soldiers, providing us with low-cost and high-speed communication services, and connecting us on the earth more closely through light.
OLT consists of core layer, service layer and public layer.
1. Core layer: provides aggregation, distribution, service process and ODN adaptation functions
2. Service layer: provides service interface and deals with various services with poor quality.
3. Public layer: provide power supply and maintenance functions
ONU and OLT are used together to realize the two-layer and three-layer functions of Ethernet, and provide voice, data and multimedia services for users.
The main functions of ONU include:
1. Receive data sent by OLT
2. Respond to the management order issued by OLT and make corresponding adjustment
3. Cache the Ethernet data of users and send it to the upline direction in the sending window allocated by OLT
4. Other user management functions
Huawei ONU equipment includes MDU and ONT. MDU is usually placed in the street cabinet, corridor, etc.; ONT is usually placed in the user's home.
Optical transmission channel ODN
ODN is an optical cable network based on PON equipment. It could establish optical information transmission channel between OLT and ONU, and achieve the information transmission and distribution function between OLT and ONU.
ODN is divided into two points and three sections from the office to the user. Two points refer to optical distribution point and optical access point, and three sections respectively refer to feeder cable, distribution cable and indoor cable.
