This sets the loopback state, no loop, payload loop, or line loop, for this DS1 port. As with its DS3 counterpart, payload loop isolates this port's framer/mapping logic while line loop reflects the signal at the physical interface, letting a technician narrow down exactly which stage of this port's hardware is at fault. A DS1 port suspected of a framer problem would be tested with dsx1PayloadLoop configured here to confirm the fault is in framing logic rather than the raw line driver.