Selective Repeat ARQ

Definition

Selective Repeat Automatic Repeat reQuest (ARQ) is an error control protocol used in data communication that enables the receiver to selectively acknowledge and request retransmission of only those frames that were received incorrectly. This approach helps improve efficiency and throughput in network communication by avoiding unnecessary retransmissions of correctly received frames, allowing for better use of bandwidth.

5 Must Know Facts For Your Next Test

1. Selective Repeat ARQ allows the receiver to buffer out-of-order frames while waiting for missing ones, enhancing the efficiency of data transmission.
2. In Selective Repeat ARQ, both the sender and receiver maintain a window size that defines how many frames can be sent or acknowledged at once.
3. The protocol employs a sequence number for each frame, allowing the receiver to identify which frames have been successfully received and which need retransmission.
4. Selective Repeat ARQ is particularly useful in environments with high error rates as it reduces the number of retransmissions needed compared to simpler protocols.
5. The implementation of Selective Repeat ARQ can lead to increased complexity in managing buffers at both the sender and receiver ends.

Review Questions

• How does Selective Repeat ARQ enhance efficiency compared to Go-Back-N ARQ?
  • Selective Repeat ARQ enhances efficiency by allowing only the specific erroneous frames to be retransmitted instead of all subsequent frames as done in Go-Back-N ARQ. This selective approach means that correctly received frames do not need to be resent, making better use of available bandwidth and reducing unnecessary data traffic. As a result, Selective Repeat ARQ can achieve higher throughput, especially in networks with variable error rates.
• What role do acknowledgments (ACKs) play in the functioning of Selective Repeat ARQ?
  • In Selective Repeat ARQ, acknowledgments (ACKs) are critical for communication between sender and receiver. The receiver sends ACKs for each correctly received frame, while negative acknowledgments (NACKs) are sent for any frames that need retransmission. This feedback mechanism allows the sender to know exactly which frames were received correctly and which were not, facilitating targeted retransmissions and improving overall transmission reliability.
• Evaluate the impact of using a sliding window protocol alongside Selective Repeat ARQ in network communications.
  • Using a sliding window protocol with Selective Repeat ARQ greatly enhances data flow management in network communications. It allows multiple frames to be sent before needing an acknowledgment, thereby increasing throughput and making better use of network resources. By maintaining a window size that balances between efficient transmission and avoiding congestion, this combination effectively addresses issues like delays and packet loss, ultimately leading to more reliable and efficient data transfer across networks.

Related terms

Go-Back-N ARQ: A protocol where if a single frame is found to be erroneous, all subsequent frames are retransmitted, which can lead to inefficiencies in data transmission.

Acknowledgment (ACK): A signal sent from the receiver to the sender indicating successful receipt of a data frame, which is crucial for protocols like Selective Repeat ARQ.

Sliding Window Protocol: A method used in networking to control the flow of data packets between sender and receiver, allowing multiple frames to be in transit before requiring acknowledgment.