Return channel
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In communications systems a return-channel (also reverse channel or back channel) is typically a low-speed, or less-than-optimal, transmission channel in the opposite direction to the main channel.
An example of this is in ADSL where "A" stands for "asymmetric", and the channel from the subscriber to the supplier (ISP), is slower and may be of less capacity than the channel from the supplier to the subscriber.
For interactive services and Internet access, the return path is used to establish a two-way communication link back to the service provider.
The back channel may not utilise the same medium as the main channel. For example interactive cable-TV services utilise a dial-up modem and telephone line to provide a back-channel.
In many cases, the back-channel is used for acknowlegements of the validity of the forward-channel's data (i.e. that the forward-channel's data passes validity tests of some sort).
