This attribute has the value on when the DLCI is in loopback mode
and off otherwise. This loopback command verbs start and stop are
used to initiate and terminate the loopback mode for a DLCI. While
loopbackState is on, the local LMI will report to the interface the A-
bit status as active. Also an active A-bit signal will be reliably
propagated across the subnet to the remote DLCI.