Codecs usually come in two types of units: rackmount for the studio and portable for the remote. Audio can be sent in either direction, and most can also pass low-speed non-audio data, allowing the remote DJ to control broadcast automation or other studio equipment via RS-232.
Most codecs are available in two configurations: a fixed unit for the recording studio and a transportable device for the distant site. Audio signals can be transmitted in either direction, and many can also convey low-speed non-audio information, allowing the remote DJ to control broadcast automation or other equipment via RS-232.