Editing Loopback (section)

==Telecommunications==
In [[telecommunications]], loopback, or a loop, is a hardware or software method which feeds a received signal or data back to the sender. It is used as an aid in debugging physical connection problems. As a test, many [[data communication]] devices can be configured to send specific patterns (such as ''all ones'') on an interface and can detect the reception of this signal on the same port. This is called a loopback test and can be performed within a [[modem]] or [[transceiver]] by connecting its output to its own input. A circuit between two points in different locations may be tested by applying a test signal on the [[telecommunication circuit|circuit]] in one location, and having the network device at the other location send a signal back through the circuit. If this device receives its own signal back, this proves that the circuit is functioning. 

A hardware loop is a simple device that physically connects the receiver channel to the transmitter channel. In the case of a network termination connector such as [[X.21]], this is typically done by simply connecting the pins together in the connector. Media such as [[optical fiber]] or [[coaxial cable]], which have separate transmit and receive connectors, can simply be looped together with a single strand of the appropriate medium. 

A [[modem]] can be configured to loop incoming signals from either the remote modem or the local [[terminal (telecommunication)|terminal]]. This is referred to as loopback or software loop.