Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 25

Two SONET rings need to be interconnected at two mutual nodes in order to ensure redundant paths under failure conditions. Draw the interconnection between two bidirectional line-switched (BLSR) SONET rings showing the primary and secondary path setups that designate the signal flows under normal and failure conditions. In designing the interface, consider the following possible failure con­ditions of the two mutual nodes:
( a ) Failure of a transmitter or receiver in one of the nodes.
( b ) Failure of an entire node.
( c ) A fiber break in the link between the two nodes.