Suppose the A, C, B devices are chain-connected,the middle is a single-core optical cable.If the point C device is disabled, all communication services will be interrupted after the A and C devices.If the optical bypass is added in the link, when the device at point C loses power, the optical protection module will automatically bypass the power loss node, so as to ensure the normal communication between nodes A and B.

The bypass function is realized by optical switching, that is, by automatically switching the default path and transmitting the information flow in the case of power interruption.When the power supply is restored at point C, the system will automatically return to the normal state (A-C-B). 

As shown in the figure：

Normally:   

A-end equipment- - -A interface (optical protection module) - - -L interface (C point equipment) - - -R (optical protection module) - - -B interface (optical protection module) - - - -B end equipment

 

Point C equipment power loss:   

A-end equipment- - -A interface (optical protection module) - - -B interface (optical protection module) - - - -B-end equipment