Patent ID: 6975811

Claim:
A method of switching optical transmission lines among terminals, a first terminal and a third terminal being initially communicating via a first optical transmission line, a second terminal and a fourth terminal being initially communicating via a second optical transmission line, a first node being located between the first terminal and the first optical transmission line as well as the second terminal and the second optical transmission line, a second node being located between the third terminal and the first optical transmission line as well as the fourth terminal and the second optical transmission line, comprising the steps of; detecting a predetermined fault condition on the first optical transmission at the second node; blocking an output to the fourth terminal from the second node; transmitting a first switch request from the second node to the first node; blocking an input from the second terminal to the first node in response to the first switch request; switching the first terminal to connect to the second optical transmission line from the first optical line transmission after the input is blocked from the second terminal; transmitting a second switch request from the first node to the second node; and switching the third terminal to connect to the second optical transmission from the first optical transmission in response to the second switch request.