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sequence number

A number on each piece of data so the receiver can put it in order and spot repeats.

TCP numbers every byte; a segment's sequence number is the number of its first byte, which lets the receiver reorder data and discard duplicates.

Examples

  • If an ACK is lost and the sensor resends reading number 7, the receiver sees 7 a second time and discards the duplicate.

  • TCP numbers bytes, not messages: a segment with seq=1001 carrying 22 bytes is followed by one starting at seq=1023.

See also

acknowledgement retransmission TCP
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