Sumit Kumar - Projects

TCP feels like magic until you're forced to rebuild a sliver of it yourself. That's exactly what our Networks Lab made us do: simulate a reliable message transmission protocol over raw UDP - no TCP allowed anywhere in the stack. We called it KTPSocket, short for "Kharagpur TCP Socket," and the goal was to make an inherently unreliable channel behave like a reliable one.

The objective

Emulate reliable end-to-end flow control over an unreliable communication medium. Concretely, the protocol had to guarantee:

• Message integrity and correct ordering, even when packets arrive scrambled
• Acknowledgment of every received message
• Retransmission on timeout, without duplicating delivered messages
• Zero reliance on TCP - everything hand-rolled over raw UDP sockets

Breaking it on purpose

To find out how reliable the protocol actually was, we didn't just test the happy path - we deliberately injected packet loss at varying probabilities and plotted how performance degraded as things got worse:

• Loss rate (P) vs. cost: the cost of reliable delivery grows non-linearly as P increases. Past P = 0.35, the curve stops being gentle and starts climbing fast.
• ACK efficiency: even under heavy loss, ACK traffic doesn't scale nearly as fast as data traffic - a decent sign the protocol design isn't wasteful.
• Network load: at P = 0.50, it took on average ~6 packets to deliver a single message successfully - a 6x overhead just to survive a coin-flip's worth of packet loss.

Building a reliable channel on top of something explicitly unreliable teaches you, viscerally, why TCP's retransmission timers and windowing schemes look the way they do. I ended up re-tuning the retransmission logic, timers, and loss-handling code more times than I'd like to admit before the numbers stopped looking suspicious.

For the full picture, I also built a live dashboard with real-time plots and Wireshark packet captures, so the loss/retransmission behavior isn't just a claim in a lab report - you can actually watch it happen.