In GPON Type C dual-attribution protection, the ONU has dual PON connections to two OLT PON ports (or two OLTs). When the protection group is configured to track the OLT’s uplink Ethernet port, a Down state on that uplink is an OLT-side trigger. The OLT initiates the protection action (forces the working/standby role swap via PON protection signaling).

A — Correct behavior: After the OLT triggers protection, the ONU’s working PON interface becomes standby, and the protect interface becomes working.

B — Correct behavior: The OLT monitors and updates the ONU uplink status as part of the protection group state machine.

C — Correct behavior: After inversion, services egress the ONU via the protect PON port toward the OLT, i.e., traffic follows the configured protect path.

D — Incorrect (answer): In this scenario the trigger is the OLT’s uplink Ethernet status, not an ONU-detected failure. Therefore the ONU does not detect the fault nor initiate the switchover; the OLT does.

(Reference: HCIP-Access V2.5 – GPON protection mechanisms; Huawei OLT protection group behavior, Type C dual-homing with uplink-tracking.)