LoopCode to be accepted from remote end to place unit in
and out of payload or fractional loopback.
standard - standard loopback code. Usually consists of the
repeated binary pattern of '00001'
alternate - alternate loopback code. Usually the inverse of
the standard pattern or '11110'.
disabled - No code is accepted, disabling an request for
remote loopback.
v54 - V.54 pattern. Used for fractional loopback.