Time synchronisation via Internet and NTP
SP offers services for synchronisation of computer clocks via Internet using the standard protocol for time distribution over the Internet, Network Time Protocol (NTP). You can read more about NTP at the pages about research within Internet and NTP but also on the official Web-site for NTP, which includes information about NTP and the synchronisation accuracy you can expect as a user. The accuracy should typically be of the order of 1 to 50 milliseconds as compared to UTC. The accuracy depends mainly on the distance to the server but also on the quality of the Internet connection. The service is free of charge to all users and is based on the two NTP-servers installed at the Swedish national laboratory for time and frequency.
The Internet addresses for the servers are:
We also offer an authenticated NTP-service that uses NTPv4 autokey (IFF identity scheme). Currently the service is under evaluation and is thus not considered official. We appreciate comments via email (time@sp.se).
- ntp3.sp.se (the server answers authenticated NTP-packets only)
SP is also co-operating with Netnod Internet Exchange in Sweden AB on the installation of NTP-servers in the Swedish Internet Exchange Points. You can read more about these servers at Netnod's webpage for timeservers.
The Internet addresses for these servers are: Gothenburg:
- ntp1.gbg.netnod.se
- ntp2.gbg.netnod.se
Stockholm:
- ntp1.sth.netnod.se
- ntp2.sth.netnod.se
Malmoe:
- ntp1.mmo.netnod.se
- ntp2.mmo.netnod.se
A great number of NTP-servers can also be found elsewhere on the Internet.
Software to access the NTP servers is already installed in most versions of UNIX and Linux as well as MacOS (version 8.5 and later). Software for other operating systems, including many versions of MS Windows, can be downloaded from the Internet. In addition to this SP has written a simple Windows-based software. The software can be downloaded from the webpage software for time.
NTP time from the Swedish Netnod Internet Exchange servers is traceable back to the Swedish National time scale UTC(SP) by using GPS CV measurements between the servers and the SP site in Borås, Sweden. You can read more about this at the webpage research within GPS.
The government has decided that SP should manage the operation and the maintenance of Netnod's servers. This includes a daily supervision and documentation of how well the servers distribute time. SP has a webpage were you as a user can follow the accuracy of the servers.