OLT

The OLT is the active device of a GPON or XGS-PON network, located in a central office, POP or street cabinet. It has PON ports, each feeding one ODN, and 10G, 25G or 100G uplinks towards the core. Depending on the split ratio, a PON port typically serves 32 or 64 ONUs, and up to 128 on some platforms. Chassis models scale to hundreds of PON ports by adding line cards, while compact 4-, 8- or 16-port units suit small and mid-sized ISPs.

The OLT authenticates ONUs by serial number, password or LOID, configures them over OMCI, runs dynamic bandwidth allocation (DBA), maps VLANs and applies service profiles. In a typical configuration, the line profile defines the T-CONT and GEM port structure, while the service profile defines how the ONU's Ethernet and telephone ports handle VLANs.

PON ports use SFP optics that determine the optical class. B+, C+ and C++ modules are common for GPON. Higher-class optics suit long or heavily split links, but on short links care must be taken not to saturate the ONU receiver. An OLT usually does not terminate subscriber sessions itself. Traffic is carried over VLANs to a BNG, where authentication happens via RADIUS.

Management is done via CLI, web interface, SNMP and the vendor's element management system (EMS). In large networks, integrating ONU inventory, optical signal levels and alarms with the subscriber management system shortens time to repair considerably.