📡 What are ARQ Protocols?

Automatic Repeat Request (ARQ) protocols ensure reliable communication by handling the retransmission of lost or corrupted data. These protocols are widely used in data link and transport layers to ensure integrity and timeliness.

🧩 Types of ARQ Protocols

  1. Stop-and-Wait ARQ:

    • Sender sends one frame, waits for acknowledgment (ACK).
    • Limitation: Low efficiency due to waiting for each frame’s acknowledgment.
    • Use Case: Simple applications where low data rate suffices.

  2. Go-back-N ARQ:

    • Sender sends multiple frames before needing an acknowledgment.
    • If an error occurs, all subsequent frames from the erroneous one are retransmitted.
    • Efficiency: Better than Stop-and-Wait, but retransmission of multiple frames can be costly.

  3. Selective Repeat ARQ:

    • Like Go-back-N, but only the erroneous frame is retransmitted.
    • Efficiency: Best performance as only the lost frame is retransmitted.

🧠 Deep Insight

ARQ protocols are the digital equivalent of reassurance in uncertain communication. Each retransmission is not a failure, but a validation of trust that data will arrive as intended.

“A protocol’s job isn’t just delivery; it’s making sure the message is received, not lost in transit.”

🧭 Performance Analysis of ARQ Protocols

  • Stop-and-Wait:

    • Simple but inefficient for high-speed communication.
    • Throughput = Frame size / (Transmission time + RTT)

  • Go-back-N:

    • Throughput improves with larger window size, but retransmissions still impact performance.

  • Selective Repeat:

    • Optimal throughput when the window size is set appropriately, offering efficient use of bandwidth with minimal retransmissions.

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