Stop and Wait ARQ Process Steps | Generated by AI
Question: In the error control technology of data communication, Stop-and-Wait ARQ is one of the common methods for error detection and retransmission. The diagram below describes the process of using Stop-and-Wait ARQ when the sender and receiver transmit data. Please write out the content of items ① to ⑥ in the diagram.
Answer:
Since the specific image mentioned in your question is not provided, I will deduce the standard content for items ① to ⑥ based on the typical workflow of the Stop-and-Wait ARQ (Automatic Repeat reQuest) protocol found in computer networking examinations and textbooks.
In a standard Stop-and-Wait ARQ diagram involving a sender and a receiver, the sequence usually depicts the transmission of frames, the handling of errors (loss or corruption), and the acknowledgment mechanism. The typical flow for such a diagram is as follows:
- Normal Transmission: The sender sends a frame with a sequence number (e.g., Frame 0).
- Acknowledgment: The receiver successfully receives it and sends an ACK (Acknowledgment) for that frame.
- Next Frame: The sender sends the next frame (e.g., Frame 1).
- Error Scenario (Loss/Corruption): A frame is sent but gets lost or corrupted in transit.
- Timeout: The sender’s timer expires because no ACK was received.
- Retransmission: The sender retransmits the same frame.
Based on this standard logic, here are the likely contents for ① to ⑥:
- ① Data Frame (e.g., Frame 0): The initial data packet sent by the sender. It typically includes a sequence number (0 or 1).
- ② ACK (Acknowledgment): The confirmation sent by the receiver indicating successful receipt of the previous frame (e.g., ACK 0 or ACK 1).
- ③ Data Frame (e.g., Frame 1): The subsequent data packet sent after receiving the first ACK.
- ④ Lost or Corrupted Frame: This represents a data frame that was transmitted but failed to reach the receiver correctly (often depicted as disappearing or marked with an ‘X’).
- ⑤ Timeout: The event at the sender side where the waiting timer expires because the expected ACK was not received within the specified time limit.
- ⑥ Retransmitted Frame: The sender resends the specific frame (identical to ④) due to the timeout.
Detailed Explanation of the Process:
- Sender sends Frame 0: The sender transmits a data frame with sequence number 0 and starts a timer.
- Receiver receives Frame 0: The receiver checks for errors. If correct, it delivers the data to the upper layer and sends back ACK 0.
- Sender receives ACK 0: The sender stops the timer and proceeds to send Frame 1.
- Frame 1 is Lost/Corrupted: In the scenario for ④, Frame 1 is lost in the channel or arrives with errors. The receiver discards it and sends nothing (or sends a duplicate ACK for the previous frame, depending on the specific variation, but in basic Stop-and-Wait, it often sends nothing).
- Sender Timeout: Since the sender does not receive an ACK for Frame 1 within the timeout period, the timeout event (⑤) occurs.
- Retransmission: The sender assumes the frame was lost and retransmits Frame 1 (⑥). The receiver then accepts this retransmitted frame and sends ACK 1.
This mechanism ensures reliable data transfer over unreliable channels by combining error detection, timeouts, and retransmissions.
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