Stop and Wait ARQ (Automatic Repeat reQuest)

In computer networking, ensuring reliable data transmission is crucial. One of the fundamental error control techniques used to achieve this reliability is Automatic Repeat reQuest (ARQ). Among the various ARQ protocols, Stop and Wait ARQ is the simplest yet effective method, where the sender transmits a frame and waits for an acknowledgment (ACK) or a negative acknowledgment (NAK) from the receiver before sending the next frame.

How Stop and Wait ARQ Works

The Stop and Wait ARQ protocol ensures that data is correctly received before moving on to the next frame. The steps of its operation are as follows:

1. Sender: Transmits a frame containing data.

2. Receiver: Checks if the frame is received without errors.

   • If received correctly, it sends an ACK (Acknowledgment) back to the sender.

   • If an error is detected, it sends a NAK (Negative Acknowledgment).

3. Sender:

   • If an ACK is received, it proceeds to send the next frame.

   • If a NAK is received, it retransmits the same frame.

4. Timeout Mechanism: If the sender does not receive an ACK or NAK within a specific time limit, it assumes the frame was lost and retransmits it.

This cycle continues until all data frames are successfully transmitted and acknowledged, ensuring reliable communication.

Characteristics of Stop and Wait ARQ

Advantages

✅ Simplicity: The protocol is straightforward to implement as it only requires basic frame tracking and acknowledgment handling.

✅ Data Integrity Assurance: Every frame is checked and confirmed by the receiver, reducing transmission errors.

Disadvantages

❌ Low Transmission Efficiency: Since only one frame is sent at a time, network resources are underutilized.

❌ Increased Latency: The sender must wait for a response before sending the next frame, leading to slower transmission speeds.

Applications of Stop and Wait ARQ

Due to its simplicity and reliability, Stop and Wait ARQ is used in environments where data accuracy is prioritized over speed. Common applications include:

• Satellite Communication: The long signal travel time makes immediate acknowledgment necessary to avoid data loss.

• Wireless Networks: To handle data corruption due to interference, retransmissions help ensure data integrity.

• IoT Devices: Low-power, low-speed networks use Stop and Wait ARQ to maintain reliable transmissions.

Limitations and Alternative Approaches

Although Stop and Wait ARQ ensures reliability, its inefficiency makes it impractical for high-speed networks. To overcome this limitation, Sliding Window ARQ protocols like Go-Back-N ARQ and Selective Repeat ARQ have been developed:

• Go-Back-N ARQ: Allows multiple frames to be sent before receiving acknowledgments. If an error occurs, all subsequent frames are retransmitted.

• Selective Repeat ARQ: Retransmits only the erroneous frames, improving efficiency over Go-Back-N.

These methods enhance transmission efficiency while maintaining reliable data transfer.

Conclusion

Stop and Wait ARQ is a fundamental error control protocol that ensures data integrity through sequential frame transmission and acknowledgment. While its simplicity makes it easy to implement, its low efficiency limits its use in high-speed networks. As a result, advanced ARQ methods like Go-Back-N and Selective Repeat ARQ are often preferred for modern communication systems.

• The differences between Go-Back-N ARQ and Selective Repeat ARQ

• Other error control techniques used in networking

• Implementation examples of Stop and Wait ARQ in programming

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