Offset & round-trip delay
04The timing exchange estimates how far the server clock is ahead and how much time the packets spent traveling.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 8 ↗
RFC 5905 · § 8EXAMPLE
4 / 4
04
Attach uncertainty information.
Filtering uses delay and dispersion along with the offset.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
The offset is an estimate shaped by path asymmetry.
- Offset θ = ((T2−T1) + (T3−T4)) / 2. A positive value means the server clock is ahead of the client.
- Round-trip delay δ = (T4−T1) − (T3−T2).
- Unequal forward and reverse delays bias the offset estimate; one exchange cannot discover that asymmetry by itself.
For example, T1=0 ms, T2=15 ms, T3=17 ms, and T4=22 ms produce offset +5 ms and round-trip delay 20 ms. The example is illustrative, not a performance guarantee.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
Privacy