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What is Automatic Repeat Request (ARQ)?

Automatic Repeat Request (ARQ): Here, we are going to learn about the Automatic Repeat Request, categories of ARQ protocols, Examples, etc.
Submitted by Anushree Goswami, on January 09, 2021

ARQ: Automatic Repeat Request

ARQ is an abbreviation of "Automatic repeat request", also known as "Automatic Repeat Query". It is an error-control technique for transmission of data in which a receiver acknowledge by sending messages signifying that it has properly received a packet and mentioned durations of time enabled to progress prior to an acknowledgment is to be received to attain trustworthy data transmission over an untrustworthy service. If the sender does not get a response prior to the timeout, it generally re-transmits the packet as late as the sender receives an acknowledgment or goes beyond an established in advance number of retransmissions.

The categories of ARQ protocols comprise:

• Stop-and-wait ARQ: Stop-and-wait ARQ also mentioned as alternating bit protocol, is a technique in telecommunications to send information among two associated devices.
• Go-Back-N ARQ: Go-Back-N ARQ is a particular request of the automatic repeat request (ARQ) protocol, in which the progression of sending carries on to send a number of frames mentioned by a window size even devoid of receiving an acknowledgment (ACK) packet from the receiver.
• Selective Repeat ARQ/Selective Reject ARQ: Selective Repeat ARQ/Selective Reject ARQ is a definite request of the automatic repeat request (ARQ) protocol used to resolve series of the succession of numbers predicament in communications.

All three protocols generally make use of a number of varieties of sliding window protocol to notify the transmitter to decide which (if any) packets require to be retransmitted. These protocols be an attribute of in the data link or transport layers (layers 2 and 4) of the OSI model.

Examples

• The Transmission Control Protocol makes use of a modification of Go-Back-N ARQ to make sure consistent transmission of data over the Internet Protocol, which does not make available assured release of packets; with Selective Acknowledgement (SACK), it uses Selective Repeat ARQ.
• The ITU-T G.hn standard, which makes available an approach to generate a high-speed (up to 1 Gbit/s) local area network using accessible presented housing wiring such as power lines, telephone lines (ADSL), and coaxial cables, etc., make use of Selective Repeat ARQ to make certain consistent transmission above earsplitting media.
• ARQ systems were extensively used on shortwave radio to make sure consistent release of data such as for telegrams. These systems appeared in structures called ARQ-E and ARQ-M, which also incorporated the facility to multiplex two or four channels.
  Some patents are present for the use of ARQ in live video input surroundings. In these elevated throughput surroundings negative acknowledgments are used to force down expenses.

Reference: Automatic repeat request

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