In the DWDM network, clock is the key factor that ensures the synchronous communication between the SC1/SC2 and the SCC. There is only one clock source at the source end in the entire network. The communication between the OSC board at other stations and the SCC must be synchronous with the clock at the source end. Otherwise, the R_SLIP alarm is generated.
During the networking commissioning, port 1 of the OSC is connected to the upstream NE and port 2 is connected to the downstream NE normally. By default, the OSC sends the line clock at port 1 to the SCC. In a certain situation, when port 2 of the OSC is connected to the upstream NE and port 1 is connected to the downstream NE, you need to configure the east clock as the clock that is sent back to the SCC manually. It is recommended, however, that you do not change the clock source that the OSC sends back the SCC.

More blog:
What’s the alarm on the OptiX OSN 1800II board restarts after power-off
Warning of Failed Cascading on the MA5616 Equipped with the JDSU GE Optical Module