This paper considers synchronization of multiple plants over networks. The effect of time-varying transmission delay is compensated by a switching observer which uses the time-stamp information. To calculate the instantaneous value of transmission delay length via the time-stamp, the clocks of sending and receiving computers must be synchronized. It is shown that the correction of the difference of the quartz frequencies of the computers and the clock adjustment via NTP (Network Time Protocol) can provide the time synchronization within a required accuracy for moderate sampling periods. Proposed method is demonstrated by an experiment of synchronization of DC-motors over a real network.