Automatic Repeat Request

Definition

Automatic Repeat Request (ARQ) is an error control method used in digital communication systems that ensures reliable data transmission by automatically retransmitting erroneous or lost data packets. This technique enhances the integrity of data communication by allowing the receiver to request the sender to resend any corrupted or missing packets, thereby maintaining a robust connection in the presence of errors.

5 Must Know Facts For Your Next Test

1. ARQ is crucial for maintaining reliable communication over noisy channels where data corruption can occur frequently.
2. There are different types of ARQ protocols, including Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ, each with varying efficiency and complexity.
3. ARQ relies on both error detection and acknowledgment mechanisms to function effectively, ensuring that only correctly received packets are processed.
4. In systems using ARQ, if a packet is not acknowledged within a certain time frame, it is presumed lost and is retransmitted automatically by the sender.
5. While ARQ improves reliability, it can introduce delays in communication due to retransmission of packets, particularly in high-error environments.

Review Questions

• How does Automatic Repeat Request enhance data transmission reliability in digital communication systems?
  • Automatic Repeat Request enhances data transmission reliability by allowing the receiver to identify and request retransmission of any erroneous or lost packets. This mechanism relies on error detection methods to determine if a packet has been received correctly. If errors are detected, the receiver sends an acknowledgment indicating the need for retransmission, ensuring that all data is accurate and complete before processing.
• Compare and contrast the different types of ARQ protocols and their effectiveness in various communication environments.
  • Different types of ARQ protocols include Stop-and-Wait ARQ, which is simple but can be inefficient due to waiting for acknowledgments after each packet, and Go-Back-N ARQ, which allows multiple packets to be sent before needing an acknowledgment, enhancing efficiency but requiring retransmission of all subsequent packets after an error. Selective Repeat ARQ improves upon this by allowing only erroneous packets to be retransmitted. The effectiveness of these protocols varies based on factors like network conditions and error rates; for instance, Selective Repeat may perform better in environments with frequent but sporadic errors.
• Evaluate the impact of using Automatic Repeat Request on network performance, particularly regarding delay and throughput.
  • Using Automatic Repeat Request impacts network performance by introducing potential delays due to the need for retransmissions when errors occur. While it ensures reliable data delivery, frequent retransmissions can lower overall throughput, especially in high-error environments where many packets may need to be resent. The balance between reliability and performance is critical; therefore, networks must consider their specific conditions and requirements when implementing ARQ protocols to optimize both delay and throughput without compromising data integrity.

Related terms

Error Detection: The process of identifying errors in transmitted data using various algorithms and techniques to ensure data integrity.

Acknowledgment: A signal sent from the receiver back to the sender indicating that a packet has been successfully received without errors.

Stop-and-Wait Protocol: A simple ARQ protocol where the sender transmits a single packet and waits for an acknowledgment before sending the next packet.