The OLT sends Ethernet frames to the GPON service(such as GPFD) processing module based on configured mapping rules between service ports and uplink ports. The GPON service processing module then encapsulates the Ethernet frames into GEM PDUs for downstream transmission using a GPON port.
GPON transmission convergence (GTC) frames containing GEM PDUs are broadcast to all ONUs connected to the GPON port.
The ONU filters the received data according to the GEM port ID contained in the GEM PDU header and retains the data only belonging to the GEM ports of this ONU. Then, the ONU decapsulates the data to Ethernet frames and sends them to end users using service ports.