ARQ (Automatic Repeat Request)

Definition

ARQ is a communication protocol for error control in data transmission where the sender automatically retransmits data packets if an error is detected. This process relies on error detection codes to ensure that the data sent over a network is accurate and complete, allowing for reliable communication even in the presence of noise or interference.

5 Must Know Facts For Your Next Test

1. ARQ uses acknowledgment signals to inform the sender whether the data was received correctly or if it needs to be resent.
2. There are various types of ARQ protocols, including Stop-and-Wait, Go-Back-N, and Selective Repeat, each differing in how they handle retransmissions.
3. The use of ARQ can significantly increase the reliability of data transmission over unreliable networks by ensuring that errors are corrected through retransmission.
4. While ARQ enhances reliability, it can introduce latency and reduce overall throughput due to the time taken for retransmissions and waiting for acknowledgments.
5. Error detection codes play a critical role in ARQ, as they help identify whether a transmitted packet has been corrupted during transit.

Review Questions

• How does ARQ improve reliability in data transmission compared to systems without error correction?
  • ARQ enhances reliability by enabling the sender to automatically retransmit data packets when an error is detected. Without ARQ, any corrupted or lost packets would go uncorrected, leading to incomplete or inaccurate data at the receiver's end. By using error detection codes to identify issues and acknowledgments to confirm successful receptions, ARQ ensures that the integrity of data transmission is maintained.
• Compare and contrast the Stop-and-Wait protocol with the Sliding Window protocol within ARQ mechanisms.
  • The Stop-and-Wait protocol requires the sender to stop and wait for an acknowledgment after sending each packet before sending the next one, which can lead to inefficiencies and increased waiting times. In contrast, the Sliding Window protocol allows multiple packets to be sent before requiring acknowledgments, thus increasing throughput and better utilizing available bandwidth. The key difference lies in how they handle the flow of packets; Stop-and-Wait is simpler but slower, while Sliding Window optimizes transmission but is more complex.
• Evaluate the implications of using ARQ in a high-latency network environment and suggest strategies to mitigate potential drawbacks.
  • In a high-latency network environment, using ARQ can lead to significant delays due to repeated retransmissions and waiting for acknowledgments. This can reduce overall throughput and increase transmission times. To mitigate these drawbacks, strategies such as implementing a Sliding Window protocol can allow for more efficient use of bandwidth by sending multiple packets before waiting for acknowledgments. Additionally, optimizing error detection codes and adjusting timeout intervals can further enhance performance in such environments.

Related terms

Error Detection Codes: Techniques used to identify errors in transmitted data, ensuring that the information received is the same as what was sent.

Stop-and-Wait Protocol: A simple ARQ method where the sender waits for an acknowledgment from the receiver before sending the next packet.

Sliding Window Protocol: An advanced ARQ method that allows multiple packets to be in transit before needing acknowledgments, improving efficiency in data transmission.