Backward channel
Encyclopedia
In a data 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.
In data transmission
, it is a secondary channel in which the direction of transmission is constrained to be opposite to that of the primary, i.e., the forward (user-information) channel. The direction of transmission in the backward channel is restricted by the control interchange circuit
that controls the direction of transmission in the primary channel
.
Source: Partly from Federal Standard 1037C
and from MIL-STD-188
Acknowledgement (data networks)
In data networking, an acknowledgment is a signal passed between communicating processes or computers to signify acknowledgment, or receipt of response, as part of a communications protocol...
, or error
Error
The word error entails different meanings and usages relative to how it is conceptually applied. The concrete meaning of the Latin word "error" is "wandering" or "straying". Unlike an illusion, an error or a mistake can sometimes be dispelled through knowledge...
-control signals. The direction of flow of these signals is opposite to that in which user information
User information
User information is information transferred across the functional interface between a source user and a telecommunications system for delivery to a destination user.In telecommunications systems, user information includes user overhead information....
is being transferred. The backward-channel bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
is usually less than that of the primary channel, that is, the forward (user information
User information
User information is information transferred across the functional interface between a source user and a telecommunications system for delivery to a destination user.In telecommunications systems, user information includes user overhead information....
) channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
. For example, ADSL
Asymmetric Digital Subscriber Line
Asymmetric digital subscriber line is a type of digital subscriber line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice...
's upstream channel, considered a backward channel for some types of analysis, typically has a bandwidth less than one-fourth of the downstream channel.
In data transmission
Data transmission
Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...
, it is a secondary channel in which the direction of transmission is constrained to be opposite to that of the primary, i.e., the forward (user-information) channel. The direction of transmission in the backward channel is restricted by the control interchange circuit
Interchange circuit
In telecommunication, an interchange circuit is a circuit that facilitates the exchange of data and signaling information between data terminal equipment and data circuit-terminating equipment ....
that controls the direction of transmission in the primary channel
Primary channel
In telecommunication, the term primary channel has the following meanings:# The channel that is designated as a prime transmission channel and is used as the first choice in restoring priority circuits....
.
See also
- Return channelReturn channelIn communications systems that use star topologies, the return channel is the transmission link from a user terminal to the central hub....
Source: Partly from Federal Standard 1037C
Federal Standard 1037C
Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....
and from MIL-STD-188
MIL-STD-188
MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...