Sequence & acknowledgment
04Sequence numbers identify byte positions. A cumulative acknowledgment names the next byte expected in order.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 3.4 ↗
RFC 9293 · § 3.4EXAMPLE
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04
Report the next expected byte.
This cumulative acknowledgment covers all bytes through 1100.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
ACK N covers the bytes before N.
- Sequence numbers wrap modulo 2³²; comparisons must account for wraparound.
- SYN and FIN each occupy one sequence number; ACK alone does not.
- Duplicate data must not be delivered twice to the application.
The example sequence numbers are illustrative. They are not guidance for selecting initial sequence numbers.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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