Time synchronisation via dial-up modem

SP provides a service for synchronising computer clocks via dial-up modem. At SP, two modems are connected to individual time code generators, the time from which is directly traceable to official Swedish time, UTC (SP). The phone number to the service is +46 33 415783, charged at normal telephone call rates.

The computer time service means that computers with modems  can call SP’s atomic clocks in order automatically to adjust their internal clocks. The time code signals follow a de-facto standard, and can therefore be used with the large number of programs available on the Internet. Alternatively, SP can supply a suitable program for the service. 

The accuracy of adjusting a computer clock via our modems is normally limited to about 0,1 seconds, due partly to propagation speed over the telephone network and partly to the relatively slow modem speed of 1200 baud.

Delay compensation

Partial compensation of the delay in the telephone network is provided by SP actually distributing the time code 50 milliseconds before the time indicated by it. Depending on from where the customer rings, this compensation is more or less correct. However, some software programs utilise the ability offered by our time code generators to echo part of the code in order to enable the delay to be calculated. If this is done, accuracy should normally be better than about 10 milliseconds. 

Description of the time code

Click "Time Code Format" in the column on the right for details of the time code as distributed by the modems (copied from the Time Code Generator Instructions), which can be used by those wishing to write their own programs.  

SP ensures that Fröken Ur always tells the right time

Fröken Ur is the Swedish speaking clock service. SP's Time and Frequency laboratory provides the time signal, while Telia distributes it from the laboratory to callers. Read more...

Time and Frequency

The main duty of the time and frequency national standards laboratory is to distribute the Swedish standard time. This is done within the framework of national and international timekeeping, time synchronisation, research and our calibration and development services. Read more...

Tid via Internet

SP tillhandahåller en service för synkronisering av datorklockor via Internet och det standardiserade Internet-protokollet, Network Time Protocol (NTP).Read more...

Related Information

Services

Time Synchronisation

Technical Areas

Measurement Technology

Documents

Contact Persons

Kenneth Jaldehag

Phone: +46 10 516 54 08

Carsten Rieck

Phone: +46 10 516 54 40

SP Technical Research Institute of Sweden, Box 857, SE-501 15 Borås Phone +46 10-516 50 00, E-mail info@sp.se