📊 Performance of ARQ Protocols

ARQ protocols are central to ensuring reliable data transmission, but their performance can vary based on factors like channel quality, window size, and protocol type. Let’s dive into the performance evaluation of Stop-and-Wait, Go-back-N, and Selective Repeat.

📈 Stop-and-Wait ARQ

Efficiency:

  • In Stop-and-Wait ARQ, the sender must wait for an acknowledgment after sending a frame, which leads to poor utilization of available bandwidth, especially in high-latency networks.

Throughput: [ \text{Throughput} = \frac{\text{Frame Size}}{\text{Transmission Time} + \text{Round-Trip Time (RTT)}} ] Where RTT represents the time for a packet to go to the receiver and back.

Limitation: It is highly inefficient in high-speed networks or long-distance communication, as the sender is idle for most of the round trip.

➡️ Go-back-N ARQ

Efficiency:

  • Go-back-N allows sending multiple frames before receiving an acknowledgment. However, if a frame is lost or corrupted, all subsequent frames must be resent, which can cause a reduction in efficiency.

Throughput:

  • Throughput increases as the sender can send more frames before waiting for an acknowledgment.

  • Window size plays a crucial role here. A large window size improves performance but may also cause congestion and out-of-order packets.

🔄 Selective Repeat ARQ

Efficiency:

  • Selective Repeat offers the highest efficiency of the three protocols. Only the lost or corrupted frame is retransmitted, not the entire window of frames.

Throughput:

  • Selective Repeat maximizes throughput by making optimal use of bandwidth and reducing the need for retransmissions.

Window size: A larger window provides better efficiency, but there are trade-offs in memory and complexity.

🧠 Deep Insight

The performance of ARQ protocols isn’t simply a matter of choosing one over another. It’s about matching the protocol to the network’s conditions. The balance between efficiency and reliability is key to deciding which ARQ protocol to use.

“In the world of ARQ protocols, efficiency is the dance, but reliability is the rhythm that keeps everything in sync.”

🧭 Key Takeaways:

  • Stop-and-Wait is simple but inefficient for high-speed or long-distance communication.
  • Go-back-N improves throughput but introduces inefficiency due to retransmitting multiple frames.
  • Selective Repeat offers optimal performance by retransmitting only the corrupted frame.

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