world time/clock reference

hi all,

I’m working on a Data Center Operation Procedures for my client, one of local banks in Indonesia.

One of the procedures, is to determine an exact reference about clock/time information, so the whole systems (including a mainframe, several iSeries and many xSeries) have the same clock/time information with the rest of the world.

I have come to several sites, but don’t know for sure whether to use their services or not.

Thanks,
JHP