A hierarchy of clocks
01Primary time servers connect to reference sources. Secondary servers and clients build a synchronization hierarchy.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 4 ↗
RFC 5905 · § 4EXAMPLE
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03
Synchronize another clock.
Each additional hop adds its own uncertainty to the time estimate.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
RFC 1305 (NTPv3)RFC 5905 §1
NTPv4 adds IPv6 accommodation, extensible packets, and revised mitigation and clock-discipline algorithms while preserving interoperability with earlier NTP versions.
Read the updated RFC section ↗A short hierarchy is useful, but stratum alone is not accuracy.
- Stratum 1 denotes a primary server synchronized to a reference source.
- A synchronized secondary system normally reports one stratum above its system peer.
- Delay, dispersion, jitter, reachability, and synchronization distance also determine whether a source is usable.
RFC 5905 specifies NTPv4 and obsoletes RFC 1305 and RFC 4330. Its algorithms improve clock estimates; they do not guarantee a universal accuracy on arbitrary networks.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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