By Svein Johannessen

n this article we examine the problem of syn-chronizing the time-of-day clock in one node of an automation network system with a reference clock. The emphasis of this article is on switched, highly loaded networks, where unpredictable delays introduce excessive syn-chronization noise. Time Stamping Time stamping is the association of a data set with a time value. In this context, time may also include the date. Why is time stamp desirable? The closest exam-ple may be on your own PC. Whenev-er you create or save a document, the document is automatically assigned a date-and-time value. This value can be used to locate documents created on a certain date (last Monday), documents cre-ated within a certain time span (last half of 1998), and the order in which a set of documents was created (the e-mails in your inbox). By looking at these examples, it can be seen that the accuracy needed for the time stamping is about the same as we expect from a wristwatch. This comparison suggests an accu-racy within a couple minutes, but as long as the clock does not stop, it does not really matter how pre-cise it is