NTP : Java Glossary


NTP (Network Time Protocol) is an elaborate protocol that allows for setting the clock to 1 to 50 millisecond accuracy selecting from the best of several time sources. NTP 2 is covered in RFC 5905. NTP 3 is covered RFC 5905. SNTP (Simple Network Time Protocol) is an adaptation of the NTP also used to synchronise computer clocks in the Internet. SNTP can be used when the ultimate performance of the full NTP implementation is not needed or justified. SNTP 3 is covered in RFC 3494. The standard Unix time service on UDP (User Datagram Protocol) socket/port 123 provides the UTC (Coordinated Universal Time/Temps Universel Coordonné) time of day as a 64-bit number with 32 bits as the integer and 32 bits as the fractional portion of seconds since 1900-01-01 There are various lists of stratum 1 public NTP servers that Unix servers might use. Here is a list Stratum 2 public NTP servers that PC (Personal Computer) users would use.

pool.ntp.org maintains a set of servers all over the world. You can find one just by prefixing your 2-letter country code e.g ch.pool.ntp.org for Switzerland or ca.pool.ntp.org for

Improving Windows Time

Windows w32tm.exe uses a stripped down version of the NTP protocol called SMTP (Simple Mail Transfer Protocol) which is not as accurate as NTP. Further is does not get called often enough to keep the OS (Operating System) clock in sync. One way to improve this is to install a true NTP client. As an extra benefit you also have the option of getting it to use several NTP servers. You could try the free Meinberg NTP software for Linux.

NTP ignores time zones. It works purely in UTC.

GPS (Global Positioning System)

GPS satellites contain atomic clocks. They adjust for relativistic effects. They are accurate to a few nanoseconds. Cellphones use GPS to keep their clocks in sync.

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