In the FTTH(Fiber to the home) network project, OLT, ONU, ONT and ODN are now widely used in the city. First, let us make the introduction.

What is OLT (Optical Line Terminal)?

The OLT is the endpoint hardware device located at the central office. It is the core component of the optical access network, which is equivalent to a switch or router in a traditional communication network and is also a multi-service providing platform. It provides fiber optic interface to the user’s passive optical network.

. Uplinks the upper-layer network and completes the uplink access of the PON (Passive Optical Network) network.

. The user equipment ONU is connected through an ODN network (consist of optical fiber and a passive optical splitter). Realize the functions of control, management and ranging of the ONU of the user equipment.

What is ONU (Optical Network Unit)?

ONU converts optical signals transmitted via fiber to electrical signals. These electrical signals are then sent to individual subscribers. In general, there is a distance or other access network between ONU and end user’s premises. Furthermore, ONU can send, aggregate and groom different types of data coming from customers and send it upstream to the OLT. Grooming is the process that optimizes and reorganizes the data stream so it would be delivered more efficiently. OLT supports bandwidth allocation that allows making smooth delivery of data float to the OLT, which usually arrives in bursts from customer. ONU could get the connection by various methods and cable types, like twisted-pair copper wire, coaxial cable, optical fiber or Wi-Fi.

What is ONT(Optical Network Terminal)?

Basically, ONU and ONT are the same devices. Belong to different standard bodies, they both refer to the user side equipment in the GEPON system. In practice, they have a little difference, ONT is located at the customer premise, and ONU is located outside the home. ONU can be working on different temperatures and weather conditions. It should resist water, winds and vandals. The ONU usually communicates with an optical network terminal (ONT), which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router.

What is ODN (Optical Distribution Network)?

ODN, an integral part of the PON system, provides the optical transmission medium for the physical connection of the ONUs to the OLTs with 20 km or farther reach. Within the ODN, fiber optic cables, fiber optic connectors, passive optical splitters, and auxiliary components collaborate with each other. The ODN specifically has five segments which are feeder fiber, optical distribution point, distribution fiber, optical access point, and drop fiber. The feeder fiber starts from the optical distribution frame (ODF) in the central office telecommunications room and ends at the optical distribution point for long-distance coverage.

The distribution fiber from the optical distribution point to the optical access point distributes optical fibers for areas alongside it. The drop fiber connects the optical access point to terminals (ONTs), achieving optical fiber drop into user homes. In addition, the ODN is the very path essential to PON data transmission and its quality directly affects the performance, reliability, and scalability of the PON system.

Conclusion:

OLT, ONU, ONT And ODN equipment are indispensable components in the GPON network system, which have been broadly used by carrier/ISP in the FTTH application.