In the WDM system, the LPT function can be applied only in a point-to-point manner.
- A fault at the access point
Figure 1 shows the application of the LPT function in the scenario of an access point failure. If the service access point becomes faulty, NE1 detects the fault of the line between NE1 and RS-A, disables the link, and sends the local link fault information to NE2. At the same time, NE1 also attempts to enable the link between NE1 and RS-A so that the services can be restored when the link recovers from the fault. After receiving the link fault information from the opposite, NE2 disables the link between NE2 and RS-B so that the equipment at both ends of the network switches to the backup network.
When detecting the recovery of the faulty link, NE1 sends the link recovery information to NE2. After receiving the link recovery information from the opposite, NE2 enables the link between NE2 and RS-B so that the services are switched back to the original WDM network.
- A fault on the service network
Figure 2 shows the application of the LPT function in the scenario of a fault on the service network. If the service network becomes faulty in one direction, for example, in the NE1-to-NE2 direction, NE2 disables the link between NE2 and RS-B when detecting the line fault on the WDM side. In addition, NE2 sends the local fault information to NE1 through the service network in the NE2-to-NE1 direction. After receiving the fault information, NE1 disables the link between NE1 and RS-A. In this manner, the links at both ends are disabled at the same time so that the services at both ends are switched to the backup network.
NOTE: If the service network becomes faulty in both directions, NE1 and NE2 detect the fault and disable the links between NE1 and RS-A, NE2 and RS-B. In addition, NE1 and NE2 sends the fault information to the opposite.
When the service network recovers, NE2 detects the recovery of the WDM-side link, enables the link between NE2 and RS-B, and sends the recovery information to NE1. After receiving the link recovery information, NE1 enables the link between NE1 and RS-A. In this manner, the links at both ends are enabled so that the services are switched back to the original WDM network.
