Automatic Repeat Request

automatic repeat request

[¦ȯd·ə¦mad·ik ri′pēt ri‚kwest]

(computer science)

A request from a receiving device to retransmit the most recent block of data. Abbreviated ARQ.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Automatic Repeat Request

(communications)

(ARQ) A modem error control protocol in which the receiver asks the transmitter to resend corrupted data.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

ARQ

(Automatic Repeat reQuest) A set of protocols for handling communications errors in which the receiving station requests retransmission if an error occurs. The ARQ is a layer 2 data link protocol (see OSI model).

Stop-and-Wait ARQ
The sender waits for an acknowledgment (ACK) before sending the next frame. If the sender does not receive an ACK within a certain amount of time, or if it receives a not-acknowledged (NAK) message, the frame is retransmitted.

Go-Back-N ARQ
Multiple frames are sent, and the sender waits for all frames to be acknowledged. If there is a NAK for any frame, or if there is no ACK for all the frames, the entire set is retransmitted.

Selective Repeat ARQ
Similar to Go-Back-N ARQ, except that only the frame that did not receive a NAK is retransmitted.

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