As a link-based protection scheme, LPT provides the required network-level protection for point-to-point private line services by means of point-to-point link state pass-through.
In the case of link state pass-through (LPT), the WDM equipment transparently transmits the state information about the links where data services, such as the GE, FE, 10GE LAN, are accessed, and requests the equipment at both ends of the network to switch to the backup network in a timely manner for communication. Then, the important services can still be normally transmitted even when the link is faulty. Among the accessed data services, the GE services are mapped to the WDM network in the GFP-F mode and the 10GE LAN services are mapped to the WDM network in the MAC transparent mapping mode.
NOTE: In GFP-F mapping mode or MAC transparent mapping mode, the data services can be transparently transmitted only on the MAC layer. In GFP-F mapping mode or MAC transparent mapping mode, the LPT function helps transparently transmit the data services on the PHY layer. In GFP-T mapping mode or bit transparently mapping mode, the data services can be transparently transmitted on the PHY layer. Hence, the LPT function is not required in GFP-T mapping mode or bit transparently mapping mode.
In engineering application, inter-user data is accessed to the network for switching through the access equipment. For details, see Figure 1.
Normally, the data between router RS-A and router RS-B is switched by the network service equipment, that is, NE1 and NE2 (OptiX WDM equipment), as shown in Figure 1-1.If the link between router RS-A and router RS-B becomes faulty, the communication between the two routers is interrupted.
If the LPT function is enabled, the equipment detects and reports the faults at the service access point and the faults in the intermediate network to the data communication equipment. Then, the data communication equipment (for example, a router) can switch to the backup network in a timely manner for communication. In this manner, important services can still be normally transmitted in case of a link fault.