OLT
acronymISP & telecom
Optical Line Terminal: the provider-side head of a PON, terminating hundreds of subscriber fibers and scheduling every upstream burst.
Lives in the central office or a street cabinet; its counterpart in the home is the ONT.
The OLT is the exchange-side terminal of a passive optical network, and it is where all the intelligence lives. It broadcasts downstream to every ONT on the splitter, grants upstream transmission slots so two subscribers never transmit at once, and enforces the service profile that determines what each line is allowed.
Because the plant between it and the subscriber is passive, the OLT is also where nearly all diagnosis happens. Optical power readings per port, ranging measurements that reveal distance, and error counters are the instruments available, and they are read from one end. A fault in the outside plant is inferred from those readings rather than observed, which is why fibre troubleshooting is a matter of interpreting numbers before anyone goes to look.