Network Time Protocol (NTP)
The Network Time Protocol (NTP) is a standard protocol for synchronizing clocks in computer networks. For synchronization, NTP uses the connectionless transport protocol UDP, whose port 123 is reserved for NTP.
NTP has existed since 1985 and was published as RFC 958. More information can be found here. The current version is the revision 4. More information can be found in the NTP Version 4 Release Notes.
Originally designed for UNIX-based operating systems, for some time it has been possible to also use NTP for Windows operating systems, which can reference the exact time from the Internet without any additional software. In addition, after a change in the registry database, they can also distribute the exact time as a server.
The NTP service synchronizes the local clock via NTP server signals. This synchronization takes place at configurable intervals. In the remaining time, NTP uses phase and frequency corrections to ensure that the time is as accurate as possible during the time when there is no connection with the server.
Simple Network Time Protocol (SNTP)
Besides NTP, there is also the Simple Network Time Protocol (SNTP). More information can be found here: Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI.
SNTP is very similar to NTP, meaning that SNTP clients can also reference the time from NTP servers. However, only one time server is used for SNTP. For SNTP, there is no influence of phase and frequency of the local timer, so it requires less computational resources. Windows 2000 uses SNTP to keep the time on your local computer up to date. This is handled by the Windows service W32Time. In Windows XP and Windows Server 2003, the dynamic link library W32time.dll has been revised so that now NTP can be used for time synchronization.
More information and downloads can be found on the NTP web site.
Time Server
A time server is a server that provides clients with the current time (time stamp). Typically, a time server gets its current time stamp from another, highly accurate time server, for example, from the atomic clock of the Physikalisch-Technische Bundesanstalt in Braunschweig.
Both the Physikalisch-Technische Bundesanstalt in Braunschweig, as well as other organizations operate public time servers that can be accessed via the Internet. Here is a small selection of time servers:
|
Name |
Site |
IP address |
Location |
|---|---|---|---|
|
ntpa2.kph |
uni-mainz.de |
134.93.132.118 |
Johannes Gutenberg-University, Institut für Kernphysik, Mainz |
|
ntp1.sul |
t-online.de |
194.25.134.196 |
Deutsche Telekom AG |
|
ntp1.sda |
t-online.de |
195.145.119.188 |
Deutsche Telekom AG |
|
ntp1 |
ptb.de |
192.53.103.108 |
Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, G |
|
ptbtime1 |
ptb.de |
192.53.103.108 |
Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, G |
|
ntp2 |
ptb.de |
192.53.103.104 |
Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, G |
|
ptbtime2 |
ptb.de |
192.53.103.104 |
Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, G |
|
ntp1 |
belwue.de |
129.143.2.23 |
BelWue |
|
ntp2 |
belwue.de |
129.143.2.33 |
BelWue |
|
ntp6 |
space.net |
195.30.0.29 |
SpaceNet AG |
|
time |
uni-potsdam.de |
141.89.64.1 |
Uni Potsdam (Port 123 - UDP) |
|
ntps1 |
gwdg.de |
134.76.10.46 |
GWDG Göttingen |
|
ntps2 |
gwdg.de |
134.76.98.232 |
GWDG Göttingen |
|
ntps3 |
gwdg.de |
134.76.249.201 |
GWDG Göttingen |
|
swisstime |
ethz.ch |
129.132.2.21 |
ETH Zürich |
|
atom |
uhr.de |
62.206.250.163 |
Forum für Zeitmessung, Berlin |
Thus, the official servers are not overloaded by constant queries if an NTP pool is used. More on the use of an NTP pool and specific instructions can be found here.