Dear Mohammad,

Link failure is generally detected by optical receivers, not only for fiber cut but also for signal degradation (i.e., excessive BER). You may get more info in references like https://www.juniper.net/documentation/en_US/junos/topics/concept/otn-signal-degrade-monitoring-understanding.html or https://www.google.com/patents/US7826745.

Additionally, upon severe degradation or fiber cut a loss-of-light (LOL) alarm could be issued to NMS/OSS systems.

Best regards,

José Luis

Dear Mohammad,

In our telecom company, we mostly use SMonitor software to prudently monitor the associated nodes of network.

http://www.fiber-optics.info/articles/overview_of_fiber_optic_communications_networks

https://dl.acm.org/citation.cfm?id=2042995

Hello.

The question would deserve to be more specific, the terms "optical" and "link" being quite loose these days.

Assuming "optical" refers to WDM and "link" to "a fiber between 2 neighbor optical nodes" (i.e. an OMS between 2 ROADMs), looking at the signal from the optical receiver's perspective isn't enough to get an accurate information because wavelengths typically span multiple links. Usual systems just rely on a supervision channel, i.e. a low rate wavelength multiplexed with others and terminated at each node, thus enabling to monitor the health of multiplexed sections.

J.