In telecommunications, a back-to-back connection is a direct connection between either: 1. * the output of a transmitting device and the input of an associated receiving device. When used for equipment measurements or testing purposes, such a back-to-back connection eliminates the effects of the transmission channel or medium. 2. * the output of a receiving device and the input to a transmitting device. The term direct may be construed as permitting a passive device such as a pad to accommodate power level constraints. Source: from Federal Standard 1037C and from MIL-STD-188