The current loopback state of the SONET/SDH interface. The
values mean:
none(0)
Not in the loopback state. A device that is not
capable of performing a loopback on this interface
shall always return this value.
facility(1)
The received signal at this interface is looped back
out through the corresponding transmitter in the return
direction.
terminal(2)
The signal that is about to be transmitted is connected
to the associated incoming receiver.
other(3)
Loopbacks that are not defined here.