Automatic repeat request (ARQ), also known as automatic repeat query, is an
error-control method for
data transmission
Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...
that uses
acknowledgements (messages sent by the receiver indicating that it has correctly received a message) and
timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) If the sender does not receive an acknowledgment before the timeout, it
re-transmits the message until it receives an acknowledgment or exceeds a predefined number of retransmissions.
ARQ is used to achieve
reliable data transmission over an unreliable
communication channel
A communication 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 in telecommunications and computer networking. A channel is used for infor ...
. ARQ is appropriate if the communication channel has varying or unknown
capacity.
Variations of ARQ protocols include
Stop-and-wait ARQ,
Go-Back-N ARQ, and
Selective Repeat ARQ. All three protocols usually use some form of
sliding window protocol to help the sender determine which (if any) packets need to be retransmitted. These protocols reside in the
data link or
transport layers (layers 2 and 4) of the
OSI model
The Open Systems Interconnection (OSI) model is a reference model developed by the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems inter ...
.
Examples
The
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, th ...
uses a variant of
Go-Back-N ARQ to ensure reliable transmission of data over the
Internet Protocol
The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
IP ...
, which does not provide guaranteed delivery of packets; with Selective Acknowledgement (SACK), it uses
Selective Repeat ARQ.
IEEE 802.11 wireless networking uses ARQ retransmissions at the data-link layer.
uses
hybrid ARQ, a mixture of high-rate
forward error correction (FEC) and ARQ. It is a high-speed
local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...
standard that can operate at data rates up to 1 Gbit/s over existing home wiring (
power lines, phone lines and
coaxial cables). G.hn uses
CRC-32C for Error Detection,
LDPC for FEC and selective repeat for ARQ.
ARQ systems are widely used on shortwave radio to ensure reliable delivery of data such as for telegrams. These systems came in forms called
ARQ-E and
ARQ-M, which also included the ability to multiplex two or four channels.
A number of patents exist for the use of ARQ in live video contribution environments. In these high throughput environments negative acknowledgements are used to drive down overheads.
See also
*
Hybrid automatic repeat request
References
*Peterson and Davie, ''Computer Networks: A Systems Approach'', Third Edition, 2003
* - Advice to link designers on link Automatic Repeat reQuest (ARQ)
Negative acknowledgement ARQfor live video
*
{{Refend
Logical link control
Error detection and correction