1. Pick a delivery problem
Each scenario restarts the puzzle. The labels 1–5 show the intended order, not the arrival order. Spaces inside each piece count as data too.
2. Inspect the inbox
Choose pieces in the order you want to rebuild them. Use Tab and Enter or Space; no dragging is needed.
3. Rebuild the message
Message preview
Choose a piece to begin.
4. Think like a network detective
- Try choosing pieces in arrival order. Does that reproduce the intended message?
- In Missing piece, can you fix the message just by reordering? Find the gap, then request a resend.
- In Duplicate delivery, compare total deliveries with unique pieces. Why should a duplicate not appear twice in the message?
The real idea — and the model's limits
TCP is a transport protocol that gives an application an ordered stream of bytes. Its reliability mechanisms use sequence numbers and retransmission to deal with lost data. This puzzle borrows those ideas: order the pieces, identify a gap, and avoid repeating duplicate data.
Our five numbered pieces are a teaching analogy, not actual TCP packets. Real TCP sequence numbers track byte positions rather than numbering packets 1–5, and recovery is automatic, not a person pressing a resend button. The lab does not model acknowledgements, checksums, timers, congestion control or connection setup. Not every internet application uses TCP.
Teacher reference: IETF RFC 9293, Key TCP Concepts. This puzzle runs locally in your browser. It does not send message pieces over a network, save answers or upload them.
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