Backward channel

In a data transmission circuit a backward channel is the channel that passes data in a direction opposite to that of its associated forward channel. The backward channel is usually used for transmission of request, supervisory, acknowledgement, or error-control signals. The direction of flow of these signals is opposite to that in which user information is being transferred. The backward-channel bandwidth is usually less than that of the primary channel, that is, the forward (user information) channel. For example, ADSL's upstream channel, considered a backward channel for some types of analysis, typically has a bandwidth less than one-fourth of the downstream channel.