In communications systems, the return channel (also reverse channel or return link) is the transmission link from a user terminal to the central hub. Return links are often, but not always, slower than the corresponding forward links. Examples where this is true include

asymmetric digital subscriber line Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...

cable modem A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial (HFC), radio frequency over glass (RFoG) and coaxial cable infrastructure. Cable modems are primar ...

mobile broadband Mobile broadband is the marketing term for wireless Internet access via mobile networks. Access to the network can be made through a portable modem, wireless modem, or a tablet/ smartphone (possibly tethered) or other mobile device. The fir ...

and

satellite internet access Satellite Internet access is Internet access provided through communication satellites. Modern consumer grade satellite Internet service is typically provided to individual users through geostationary satellites that can offer relatively high d ...

. The return channel need not use the same medium as the main channel. For example, some hybrid Internet access services use a one-way

cable television Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with bro ...

system for the forward channel and a

dial-up modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carr ...

for the return channel. Even when the return and forward channels use the same medium, their differences often dictate the use of very different data

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...

and coding techniques. For example, in a star radio network, only the central hub transmits on the forward link, so

channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical m ...

is a consideration only on the return link. The "forward/return" terminology is also used for

spacecraft communication A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

links for command and

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', "remote", an ...

. Because the return link carries telemetry, often including imagery, it is often orders of magnitude faster than the forward link that transmits only a few predefined spacecraft commands. Return and forward channels are distinct from, and should not be confused with, uplinks and downlinks in satellite communication systems. For example, satellite internet access with conventional

bent-pipe transponder A communications satellite's transponder is the series of interconnected units that form a communications channel between the receiving and the transmitting antennas. It is mainly used in satellite communication to transfer the received signals. ...

s require a total of two uplinks and two downlinks. One uplink and downlink pair are used for the forward link from the central ground hub through the satellite to the user terminal, and another uplink/downlink pair are used for the return link from the user terminal to the central hub.

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{{telecommunications-stub Communication circuits

See also

External links