RFC 9293 / RELIABLE TRANSFER

Loss & retransmission

The sender keeps unacknowledged data and retransmits when loss recovery requires it.

Related RFCs and changes

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RFC 9293 · § 3.8.1EXAMPLE

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Deliver the missing bytes.

The receiver acknowledges the now-contiguous sequence.

Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references

WHAT CHANGED

RFC 793 § 3.7RFC 9293 § 3.8.1

The early illustrative RTO procedure is replaced by a requirement to use RFC 6298. RFC 9293 § 5 documents the update chain.

KEY POINT

Adapt the timeout to the path.

Compute the RTO using RFC 6298, including Karn’s algorithm for RTT sampling.
Timeout recovery retransmits unacknowledged data and backs off the timer.
A delayed or lost ACK can cause a retransmission even when the original data arrived.

DETAILS

This animation shows timer-based recovery. Fast retransmit and other recovery techniques also exist; a timeout is not the only trigger.

Diagrams simplify the RFC. Read the linked sections for complete requirements.

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