Down indicates that the SONET/SDH line in at least one direction on a bidirectional link is degraded to the point of no longer passing traffic.

The East/West directionality for each topological link is determined during discovery.

The symptoms for TopologicalLink Down are as follows:

  • LOS from downstream PTP connected to the TopologicalLink

  • RFI for the upstream PTP connected to the TopologicalLink

  • Signal Failure (SF) on the receiving PTP connected to the TopologicalLink