In
communications system
A communications system or communication system is a collection of individual telecommunications networks, transmission systems, relay stations, tributary stations, and terminal equipment usually capable of interconnection and interoperat ...
s, 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 link
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...
s. Examples where this is true include
asymmetric digital subscriber line,
cable modems,
mobile broadband and
satellite internet access.
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 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, pl ...
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,
uplink
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
s and
downlink
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...
s in
satellite communication
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...
systems. For example, satellite internet access with conventional
bent-pipe transponders 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.
See also
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Backward channel
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Upstream (networking)
In computer networking, upstream refers to the direction in which data can be transferred from the client to the server ( uploading). This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually a ...
*
Backhaul (telecommunications)
In a hierarchical telecommunications network, the backhaul portion of the network comprises the intermediate links between the core network, or backbone network, and the small subnetworks at the ''edge'' of the network.
The most common network t ...
External links
Online Video Downloader
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Communication circuits