Go Back N vs. Selective Repeat

Attribute	Go Back N	Selective Repeat
Window Size	Fixed	Variable
Retransmission	Entire window	Individual packets
Receiver Buffer	Single buffer	Multiple buffers
ACKs	Positive ACKs	Selective ACKs

Overview

When it comes to data transmission in computer networks, two popular protocols are Go Back N and Selective Repeat. Both protocols are used for automatic repeat request (ARQ) in order to ensure reliable delivery of data over unreliable networks. While they both serve the same purpose, there are key differences in how they operate and the trade-offs they make in terms of efficiency and complexity.

Go Back N

Go Back N is a sliding window protocol that allows the sender to transmit multiple frames before receiving an acknowledgment from the receiver. In this protocol, the sender continues to send frames until it reaches the window size, at which point it stops and waits for acknowledgments. If an acknowledgment is not received within a certain time frame, the sender retransmits all unacknowledged frames from the beginning of the window.

• Sender can send multiple frames before receiving acknowledgment
• If acknowledgment is not received, sender retransmits all unacknowledged frames
• Simple implementation
• Efficient use of bandwidth
• Potential for unnecessary retransmissions

Selective Repeat

Selective Repeat is another sliding window protocol that allows the sender to transmit multiple frames before receiving an acknowledgment. However, in this protocol, the sender only retransmits the specific frame that was not acknowledged by the receiver, rather than retransmitting all unacknowledged frames. This can lead to more efficient use of bandwidth and reduced unnecessary retransmissions compared to Go Back N.

• Sender can send multiple frames before receiving acknowledgment
• Only retransmits specific frame that was not acknowledged
• More complex implementation compared to Go Back N
• Efficient use of bandwidth
• Reduced unnecessary retransmissions

Comparison

While both Go Back N and Selective Repeat are sliding window protocols that allow the sender to transmit multiple frames before receiving acknowledgments, they differ in how they handle retransmissions. Go Back N retransmits all unacknowledged frames when a timeout occurs, while Selective Repeat only retransmits the specific frame that was not acknowledged. This difference can lead to more efficient use of bandwidth and reduced unnecessary retransmissions in Selective Repeat compared to Go Back N.

However, Selective Repeat is more complex to implement compared to Go Back N, as it requires the sender and receiver to keep track of individual frames and their acknowledgments. This added complexity can make Selective Repeat less desirable in certain situations where simplicity is preferred over efficiency.

Overall, the choice between Go Back N and Selective Repeat depends on the specific requirements of the network and the trade-offs between efficiency and complexity. While Selective Repeat offers more efficient use of bandwidth and reduced unnecessary retransmissions, Go Back N may be preferred in situations where simplicity is key and the potential for unnecessary retransmissions is acceptable.