Response to OTUk-BDI for OTN Interfaces to Restore Bidirectional Communications

A method of operating an OTN comprising:

• sending a plurality of OTN frames from a first network element to a second network element;
• detecting a failure in said sending step;
• switching routing from said second network element to said first network element in response to said failure detecting step and sending a BDI signal from said second network element to said first network element;
• and
• generating an alarm indication signal for said first network element so that said first network element switches routing from said first network element to said second network element in response;
• whereby said routing switching is performed bidirectionally.

An OTN interface apparatus for a first network element in an optical network, said OTN interface apparatus comprising:

• means for sending a plurality of OTN frames to a remote network element;
• means for receiving a BDI signal from said remote network element in response to a transmission failure of said plurality of said OTN frames to said remote network element;
• and
• means for generating an alarm indication signal for said first network element so that said first network element switches routing to said remote network element in response.