Explanation
Stop-and-Wait ARQ (Automatic Repeat reQuest) Protocol:
Working:
1. Sender: Sends a single frame and waits for an acknowledgment (ACK) from the receiver.
2. Receiver: Receives the frame, checks for errors, and sends an ACK if the frame is error-free. If errors are detected, a Negative ACKnowledgment (NAK) is sent.
3. Sender: If an ACK is received, it sends the next frame. If a NAK is received or a timeout occurs, it retransmits the same frame.
Example:
• Sender sends Frame 1.
• Receiver receives Frame 1, sends ACK 1.
• Sender receives ACK 1, sends Frame 2.
Go-Back-N ARQ (Automatic Repeat reQuest) Protocol:
Working:
1. Sender: Sends multiple frames without waiting for individual acknowledgments.
2. Receiver: Receives frames and sends cumulative ACK for the last correctly received frame. If an error is detected, it discards the frame and sends a NAK for the last correctly received frame.
3. Sender: If a NAK is received or a timeout occurs, it retransmits all frames from the last ACKnowledged frame.
Example:
• Sender sends Frames 1, 2, 3, 4.
• Receiver receives Frames 1, 2, 4, discards 3 (error detected).
• Receiver sends NAK 2.
• Sender retransmits Frames 2, 3, 4.
Key Differences:
• Stop-and-Wait:
◦ One frame sent at a time.
◦ Efficient for low error rates and short distances.
• Go-Back-N:
◦ Multiple frames sent before waiting for acknowledgments.
◦ Efficient for higher error rates and longer distances.
Advantages and Disadvantages:
• Stop-and-Wait:
◦ Advantage: Simple and easy to implement.
◦ Disadvantage: Inefficiency for longer propagation delays.
• Go-Back-N:
◦ Advantage: Higher efficiency for longer distances and higher error rates.
◦ Disadvantage: Complexity increases, and there is a potential for retransmitting more frames than necessary.
Considerations:
• Timeouts:
◦ Both protocols use timeouts to determine when to retransmit frames.
• Acknowledgment:
◦ Stop-and-Wait acknowledges each frame individually.
◦ Go-Back-N acknowledges multiple frames cumulatively.
These protocols play a crucial role in ensuring reliable data transmission over unreliable channels by handling errors and retransmissions effectively. The choice between Stop-and-Wait and Go-Back-N depends on the specific requirements and characteristics of the communication channel.