If a PON system is considered as a black box, the external interfaces of OLTs...

In a PON system, the OLT (Optical Line Terminal) and ONU (Optical Network Unit) use Ethernet interfaces externally to connect to the service provider’s network and end-user devices, respectively. Internally, the PON uses GEM (GPON Encapsulation Method) frames to encapsulate and decapsulate data for transmission over the optical distribution network (ODN).