Selective Repeat ARQ

Definition

Selective Repeat Automatic Repeat reQuest (ARQ) is a data link layer error control method that allows the receiver to selectively acknowledge and request retransmission of only those data frames that are found to be erroneous. This technique enhances efficiency by minimizing the amount of data that needs to be resent, particularly in environments with high error rates. By allowing the receiver to accept and buffer correctly received frames while retransmitting only the lost or corrupted ones, it optimizes the overall performance of data transmission.

5 Must Know Facts For Your Next Test

1. Selective Repeat ARQ operates by using a sliding window protocol that allows multiple frames to be in transit before needing an acknowledgment.
2. This method reduces the number of retransmissions required compared to Stop-and-Wait ARQ, making it more efficient for high-latency networks.
3. In Selective Repeat ARQ, both the sender and receiver maintain sequence numbers to keep track of sent and acknowledged frames, ensuring data integrity.
4. The receiver can buffer out-of-order frames until any missing frames are received, allowing for smooth data flow without waiting for previous frames to be resent.
5. Selective Repeat ARQ is particularly beneficial in wireless communication systems where data corruption rates are higher, as it minimizes unnecessary retransmissions.

Review Questions

• How does Selective Repeat ARQ improve upon traditional Stop-and-Wait ARQ in terms of data transmission efficiency?
  • Selective Repeat ARQ improves upon Stop-and-Wait ARQ by allowing multiple frames to be sent before waiting for an acknowledgment. This sliding window approach means that while one frame is being acknowledged, additional frames can continue to be transmitted. This significantly reduces idle time and improves overall throughput, especially in environments with longer round-trip times, making it more efficient than the basic Stop-and-Wait method.
• Discuss the role of frame buffering in Selective Repeat ARQ and how it affects data transmission reliability.
  • Frame buffering plays a crucial role in Selective Repeat ARQ as it allows the receiver to temporarily store out-of-order or correctly received frames until any missing or erroneous frames are retransmitted. This capability ensures that the receiver can maintain a consistent stream of data processing without interruption. By buffering these frames, the system can optimize the utilization of bandwidth and improve reliability, as it does not require all previous frames to be resent when only specific ones have errors.
• Evaluate the impact of using Selective Repeat ARQ in high-error-rate environments compared to other ARQ methods.
  • In high-error-rate environments, Selective Repeat ARQ offers a significant advantage over methods like Go-Back-N or Stop-and-Wait ARQ due to its ability to selectively retransmit only those frames that were lost or corrupted. This targeted approach reduces unnecessary bandwidth consumption and enhances overall network efficiency. Additionally, by maintaining a buffer for out-of-order frames, Selective Repeat ARQ can minimize delays and improve throughput in conditions where multiple packets may be lost simultaneously, thus maintaining a smoother data transmission experience.

Related terms

Stop-and-Wait ARQ: A simpler error control method where the sender transmits one frame and waits for an acknowledgment before sending the next, which can lead to inefficiencies especially over long distances.

Go-Back-N ARQ: A more advanced error control technique where the sender can transmit several frames before needing an acknowledgment but must retransmit all frames starting from the erroneous one.

Frame Buffering: The process of temporarily storing received data frames in memory until they can be processed or acknowledged, essential for techniques like Selective Repeat ARQ.