Automatic Repeat Query (ARQ) (Cambridge (CIE) IGCSE Computer Science)

Revision Note

Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

Automatic Repeat reQuests(ARQ)

What is an automatic repeat request(ARQ)?

  • An automatic repeat request is a protocol that notifies the sender that an error has occurred and that the data received is incorrect

  • It works as follows:

    • If an error is detected the receiver sends a negative acknowledgement transmission to indicate the data is corrupted

    • If no error is detected the receiver sends a positive acknowledgement transmission meaning the data is correct

    • If the receiver does not send any acknowledgement transmission then the sender waits for a certain time period known as a time-out before automatically resending the data

    • This process is repeated until all data has been received and acknowledged

Examiner Tips and Tricks

In this specification ARQ is referred to as Automatic Repeat Query but in past exam questions it has been referred to as Automatic Repeat reQuests

Both words are interchangeable and should not cause any confusion!

Worked Example

Explain how Automatic Repeat reQuests (ARQ) are used in data transmission and storage

[2]

Answer

Any two from:

  • Set of rules for controlling error checking/detection // it’s an error detection method // used to detect errors

  • Uses acknowledgement and timeout

  • Request is sent (with data) requiring acknowledgement

  • If no response/acknowledgment within certain time frame data package is resent

  • When data received contains an error a request is sent (automatically) to resend the data

  • The resend request is repeatedly sent until packet is received error free/limit is reached/acknowledgement received

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Robert Hampton

Author: Robert Hampton

Expertise: Computer Science Content Creator

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.