Time synchronization measurements with a combination of a GPS receiver andthe internet

At present, the global positioning system (GPS) is the best way for worldwi de time transfer, in all the scientific and practical applications, both fo r its accuracy and reliability. Evidence of this is also available to unive rsity students in physics, through simple experimental activities, today ma de possible by the low cost of GPS modules dedicated to timing. The 1PPS (o ne peak per second) pulse, made available by such receivers, brings into a teaching laboratory the stability of an ensemble of atomic clocks, capable of very accurate frequency (which we have described previously) and time me asurements. In fact, for the last year, we have also utilized the 1PPS pulse as the tim e reference for a time server, suitable for distributing accurate and relia ble time information through the internet. This paper shows the learning op portunities we have found for understanding how a remote clock synchronizat ion can be achieved, even in an open, non-dedicated network like the intern et. The combination of a modern measuring tool, like the GPS, and the easy access through the internet to time servers spread around the world, make i t possible to extract useful information from the comparison of one server against the others. Direct activities by students, on setting-up their computer for a special a pplication, making actual measurements with the instruments available in th e teaching laboratory, verifying in real time the typical performance. of t he network and so on, have been a trigger for their interest. We feel that such exercises can help them to gain a deeper knowledge of these modern ins truments, in spite of their advertised utilization only as 'black boxes', t oo sophisticated to be clearly understood.