Network Time Protocol

The Network Time Protocol (NTP) is a protocol for distributing the Coordinated Universal Time (UTC) by synchronizing the clocks of computer systems over IP networks.

NTP is one of the oldest Internet Protocols still in use (since before 1985) and uses UDP port 123.

Network Time Protocol Media

NTP was designed by David L. Mills.
The U.S. Naval Observatory Alternate Master Clock at Schriever AFB (Colorado) is a stratum 0 source for NTP
Yellow arrows indicate a direct connection; red arrows indicate a network connection.
Round trip delay time δ
The NTP management protocol utility ntpq being used to query the state of a stratum 2 server.
chronyc, showing sources and activity information. Terminal window under Arch Linux

Mills, David L. (24 March 2006). Computer Network Time Synchronization: The Network Time Protocol. Taylor & Francis / CRC Press. ISBN 0849358051.

NTP Public Services Project This is the home for the NTP (Network Time Protocol) Public Services Project which provides public support for the NTP Project and the IETF NTP Working Group. Also a Wiki with lists of NTP servers.
IETF NTP working group
David Mills' NTP project page
NTP version 4 Release Notes
Time and NTP paper
NTP Articles and News Archived 2008-09-27 at the Wayback Machine - A collection of NTP related articles and news
NTP Survey 2005 Archived 2019-05-04 at the Wayback Machine
Network Time Protocol Archived 2008-05-01 at the Wayback Machine - National Research Council of Canada
Network Time Server - NTP time server software for Windows
Online NTP Test Utility - Tests a NTP Server which is public to the internet
A Brief Guide to NTP Archived 2009-02-18 at the Wayback Machine - Google Knol on NTP
Time Synchronisation Blog Archived 2008-10-19 at the Wayback Machine

Daytime protocol DAYTIME synchronization protocol via TCP or UDP port 13
ICMP protocol Time synchronization with ICMP timestamps (basis for timed )
HTTP Time Protocol (HTP) Time synchronization with HTTP headers
Reference-Broadcast Synchronization (RBS) Archived 2008-08-22 at the Wayback Machine Time synchronization for wireless networks
Time protocol Time synchronization protocol via TCP or UDP port 37

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