How does a sliding window flow control mechanism benefit the EPD Pilot protocol?

• A. It increases channel latency.
• B. It eliminates the need for checksums.
• C. It guarantees packet ordering without buffering.
• D. It limits in-flight frames, balances throughput with network capacity, and supports ordered delivery despite varying latencies.

Answer: (D)

Sliding window flow control creates a moving limit on how many frames can be in transit before an acknowledgment is received, forming a productive data pipeline between sender and receiver. In the EPD Pilot protocol this keeps the link busy to maintain high throughput while preventing the network or receiver from being overwhelmed. Because the sender adjusts based on acknowledgments, the window can expand or contract with changing network conditions, balancing throughput with available capacity. With sequence numbers and a small receive buffer, the receiver can place arriving frames in order, even when some take longer to reach it, so delivery remains ordered despite varying latencies. This combination—limiting in-flight frames, matching the pace to network capacity, and supporting ordered delivery under latency variation—best describes the benefit of sliding window in this context. Checksums are still needed for integrity, and ordering typically relies on buffering; a sliding window alone does not guarantee order without buffering, and it does not inherently increase channel latency.