The current loopback state of the SONET/SDH interface.
The values mean:
sonetNoLoop Not in the loopback state. A device that is not
capable of performing a loopback on this interface
shall always return this value.
sonetFacilityLoop The received signal at this interface is looped back
out through the corresponding transmitter in the
return direction.
sonetTerminalLoop The signal that is about to be transmitted is
connected to the associated incoming receiver.
sonetOtherLoop Loopbacks that are not defined here.