How to distinguish between optical access network OLT, ONU?

How to distinguish between optical access network OLT, ONU, ODN, and ONT?

An optical access network uses light as the transmission medium, replacing copper wires and providing access to every home. An optical access network generally consists of three components: the optical line terminal (OLT), the optical network unit (ONU), and the optical distribution network (ODN). The OLT and ONU are the core components of the optical access network.

What is an OLT?

An OLT stands for Optical Line Terminal. It's a central office device in telecommunications, connecting to fiber optic trunk lines. It functions like a switch or router in traditional communications networks, serving as both the gateway to the external network and the exit/entry point to the internal network. Located at the central office, its most important functions include traffic scheduling, buffer control, providing a user-facing passive optical network interface, and allocating bandwidth. Simply put, it performs two functions: upstream access to the PON network; and downstream, it distributes acquired data via the ODN network to all ONU user terminals.

What is an ONU?

An ONU stands for Optical Network Unit. An ONU has two functions: selectively receiving broadcasts from the OLT and responding to the OLT if the data needs to be received; and collecting and buffering Ethernet data sent by users and sending this buffered data to the OLT according to the assigned transmit window.

In FTTx networks, different ONU access methods vary. For example, FTTC (Fiber to the Curb) ONUs are placed in the central equipment room of a residential building; FTTB (Fiber to the Building) ONUs are placed in junction boxes in the hallway; and FTTH (Fiber to the Home) ONUs are placed in households.

What is the relationship between the ONU and the OLT?

The OLT is the management terminal, and the ONU is the terminal. Service provisioning for the ONU is issued by the OLT, creating a master-slave relationship between the two. Multiple ONUs can be connected to one OLT using an optical splitter.