Stop-and-wait ARQ

Definition

Stop-and-wait ARQ (Automatic Repeat reQuest) is a simple error control protocol used in data communications, where the sender transmits a single frame and then waits for an acknowledgment from the receiver before sending the next frame. This method ensures reliable data transfer by retransmitting lost or corrupted frames, making it a foundational strategy in error handling for network communications.

5 Must Know Facts For Your Next Test

1. Stop-and-wait ARQ is easy to implement but can be inefficient in high-latency networks due to the idle time while waiting for acknowledgments.
2. In stop-and-wait ARQ, if an acknowledgment is not received within a specified timeout period, the sender assumes the frame was lost and retransmits it.
3. This method can lead to underutilization of network resources because only one frame is in transit at any given time.
4. The protocol ensures that only frames that have been positively acknowledged are considered successfully transmitted.
5. Variations of stop-and-wait ARQ exist, such as sliding window protocols, which aim to improve efficiency by allowing multiple frames to be in transit before needing an acknowledgment.

Review Questions

• How does stop-and-wait ARQ handle errors in data transmission, and what is its impact on overall network performance?
  • Stop-and-wait ARQ handles errors by requiring the sender to wait for an acknowledgment after each frame is sent. If an acknowledgment isn't received within a timeout period, the sender retransmits the frame. While this method ensures reliable delivery, it can significantly impact network performance by introducing delays and underutilizing bandwidth, especially in networks with high latency.
• Discuss the efficiency challenges of stop-and-wait ARQ compared to more advanced protocols like sliding window protocols.
  • Stop-and-wait ARQ faces efficiency challenges because it allows only one frame to be in transit at any time. This results in idle periods while waiting for acknowledgments, making it less effective in high-bandwidth or long-distance connections. In contrast, sliding window protocols allow multiple frames to be sent before needing an acknowledgment, which maximizes network throughput and reduces wait times, ultimately leading to better utilization of resources.
• Evaluate the scenarios where stop-and-wait ARQ would be preferable over more complex error control protocols.
  • Stop-and-wait ARQ may be preferable in simpler communication systems or scenarios with low data transmission rates and minimal delay, where the overhead of more complex protocols isn't justified. It is also suitable for applications where reliability is critical but traffic load is light, allowing for straightforward implementation without additional complexity. For example, in small-scale sensor networks or simple telemetry applications, stop-and-wait ARQ's simplicity and reliability can effectively meet requirements without unnecessary complications.

Related terms

Acknowledgment: A signal sent from the receiver to the sender indicating that a frame has been successfully received.

Frame: A data packet that includes both the payload (actual data) and control information used for transmission over a network.

Timeout: A mechanism that determines how long the sender will wait for an acknowledgment before retransmitting a frame.