A technique for testing the digital processing circuitry of a communications device. It can be initiated locally or remotely via a telecommunications circuit; the device being tested will echo back a [..]

A mechanism incorporated into a terminal or into equipment in the network whereby a duplex communication path may be connected back upon itself so that the digits sent on the transmit path are returned on the receive path. [After T1.206-1994] Note: Loopback tests should be used only to check for circuit continuity and not for more subtle performanc [..]