Networking also: Network Time Protocol

NTP

Synchronises clocks within milliseconds across the internet.

In plain terms

RFC 5905. Stratum 0 = atomic clocks/GPS, stratum 1 = directly attached, etc. PTP (Precision Time Protocol) for sub-microsecond datacenter sync.

Origin

David Mills designed NTP at the University of Delaware in 1985. NTPv4 is RFC 5905 (2010). PTP (IEEE 1588) provides sub-microsecond sync in datacenters.

Where it shows up in production

pool.ntp.org Volunteer-run pool serving hundreds of millions of NTP queries daily.
Datacenter PTP Google, Facebook deploy PTP for sub-microsecond clock sync between machines.

Sources & further reading

RFC RFC 5905 — NTPv4
Blog Cloudflare — Roughtime

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