The auxiliary channel has a narrow bandwidth and, like the transmission channel, can be operated in half- duplex or duplex. However, it has a much lower transmission speed than the home channel and usually has separate interface lines.
Auxiliary channels with half duplex operation work with direction switching. If direction switching is not required during transmission, the additional auxiliary channel interface lines can be omitted; this is then referred to as asymmetrical duplex operation.
Auxiliary channel technology is used in network monitoring and modems, among other applications. In network monitoring, the various network components communicate via the auxiliary channel; in modem technology, it is specified by the International Telecommunication Union( ITU) as an acknowledgement channel. Thus with V.23.