Both the ONU and OLT check the link status and determine whether to trigger protection switching based on the link status.
If the OLT detects a fault on link A in Figure 1, it automatically switches to the protection-side link and uses the protection-side link to send messages to ONU 1 to notify that protection switching has occurred. In addition, the OLT notifies ONU 1 of the switching cause.
If ONU 1 detects a fault on link A in Figure 1, it automatically switches to the protection-side link and sends messages to the OLT to notify that protection switching has occurred. In addition, the ONU notifies the OLT of the switching cause.
After switching, services on ONU 1 are transmitted to the OLT through the protection port, all the backbone fibers connected to the OLT transmitted service packets, and ONU N is not affected. The changes on ONU 1 are as follows:
The state of the working port changes to standby.
The state of the protection port changes to active, and service packets are transmitted through link B in Figure 1.
After protection switching, ONU 1 can automatically switch back to the working port. The OLT sends an automatic switchback message and the switchback time, called the wait to restore (WTR) time, to the ONU.
If the OLT learns that ONU 1's working port and the working-side line are functioning properly and the working-side line stays normal during the WTR time, the OLT automatically switches back to the working-side line when the WTR time expires. In addition, the OLT notifies the ONU of the switching and switching cause.
If ONU 1 learns that its working port and the working-side line are functioning properly and the working-side line stays normal during the WTR time, the ONU automatically switches back to the working-side line when the WTR time expires. In addition, the ONU notifies the OLT of the switching and switching cause.