This table contains methods to control the loopback state of
the local link as well as indicating the status of the
loopback function.
Loopback can be used to place the remote OAM entity in a state
where every received frame (except OAMPDUs) are echoed back
over the same interface on which they were received. In this
state, at the remote entity, 'normal' traffic is disabled as
only the looped back frames are transmitted on the interface.
Loopback is thus an intrusive operation that prohibits normal
data flow and should be used accordingly.