What are the ways to find faults

Hello, there are usually the following methods:

I hope my answer is helpful to you!

The general fault isolation rules are as follows:

Locate external faults first, followed by internal faults.
Locate network faults first, followed by NE faults.
Locate high-severity alarms first, followed by low-severity alarms.
Locate multi-channel signal alarms first, followed by single-channel signal alarms.
Locate bidirectional signal alarms first, followed by unidirectional signal alarms.
Locate public alarms first, followed by individual alarms.

https://support.huawei.com/enterprise/en/doc/EDOC1000152976?section=j005

Hi
I want to add something that is really useful .
In WDM there is an optical signal called ( optical supervisory channel ) OSC this signal is generated from board separated of the main signal path usually called SC2/SC1 this signal sent with the main signal .
So now u have 2 cases:
1- If u find cut alarm in the main signal boards (like OAU , OPU , D40,OBU.....) and in the OSC (for example SC2/SC1 ....)supervisory channel that means u have cable cut.
2-If u have alarm in the main signal boards (like OAU , OPU , D40,OBU.....) but no alarm in the OSC channel that means u have fault in the DWDM main signal boards either in the transmit or in the receive side , u can determin that by checking alarms .
Best regards