Time synchronisation via dial-up modemSP 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.
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.