Like every other field, PON technology has its own terminology
- the CO head-end is called an OLT
- ONUs are the CPE devices (sometimes called ONTs in ITU)
- the entire fiber tree (incl. feeder, splitters, distribution fibers) is an ODN
- all trees emanating from the same OLT form an OAN
- downstream is from OLT to ONU (upstream is the opposite direction)
PON Architecture Diagram:
OLT (Optical line terminal)
OLT is a terminal equipment connected to the fiber backbone. It sends Ethernet data to the ONU, initiates and controls the ranging process, and records the ranging information. OLT allocates bandwidth to the ONU and controls the starting time and the transmission window size of the ONU transmission data.
ODN (Optical Distribution Network)
ODN is a FTTH fiber optic cable network based on PON equipment. Its role is to provide optical transmission channel between the OLT and ONU. According the function, ODN from the central office to the client can be divided into four parts:
- feeder fiber optic subsystems,
- cable wiring subsystem,
- home line of fiber optic subsystems
- and fiber terminal subsystems.
The main components in ODN include optical fibers,optical connectors,optical splitters and corresponding equipments for installing them.
ONU (Optical network unit)
ONU is a generic term denoting a device that terminates any one of the endpoints of a fiber to the premises network, implements a passive optical network (PON) protocol, and adapts PON PDUs to subscriber service interfaces. In some contexts, ONU implies a multiple subscriber device. Optical Network Terminal (ONT) is a special case of ONU that serves a single subscriber.