Editing Loopback (section)

{{Short description|Routing of signals back to their source}}
{{Other uses|Loop line (disambiguation){{!}}Loop line}}
{{More citations needed|date=August 2020}}

'''Loopback''' (also written '''loop-back''') is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure.

Loopback can take the form of communication channels with only one [[communication endpoint]]. Any message transmitted by such a [[Communication channel|channel]] is immediately and only received by that same channel. In telecommunications, loopback devices perform [[transmission (telecommunications)|transmission]] tests of [[Access network|access]] lines from the serving [[switching center]], which usually does not require the assistance of personnel at the served [[terminal (telecommunication)|terminal]]. [[Loop around]] is a method of testing between stations that are not necessarily adjacent, wherein two lines are used, with the test being done at one station and the two lines are interconnected at the distant station. A [[patch cable]] may also function as loopback, when applied manually or automatically, remotely or locally, facilitating a loop-back test.

Where a system (such as a [[modem]]) involves round-trip analog-to-digital processing, a distinction is made between '''analog loopback''', where the analog signal is looped back directly, and '''digital loopback''', where the signal is processed in the digital domain before being re-converted to an analog signal and returned to the source.