In pace with the technical progress in controllability of mechatronic systems including machines and industrial equipment, the systems of industrial controllers (both PLC and microprocessor ones) more and more frequently use Ethernet-based networks for communication with supervising centres and surveillance systems. The Internet offers unsurpassed opportunities of remote programming as well as remote development, debugging and tuning the existing control software. Nowadays, supporting the remote tools and facilities is the essential requirement that is mandatory when decisions on purchase and implementation of industrial controllers are made. It is the underlying reason to launch more extensive research in that field. The presented paper describes dedicated software that has been developed to enable communication over the Internet within dispersed control systems. The system makes it possible to transmit and to receive short messages to and from the controlled actuators as well as to perform basic tasks related to management of data flow in networks that use TCD and UDP protocols. The special attention was paid to dynamic phenomena of the data exchange process. It is an issue of crucial importance within dispersed systems of industrial controllers and it assures efficient operation of the entire system owing to timely and quick respond to fast-changing control signals. Data exchange was carried out with the use of so-called primitives for Berkeley sockets that serve as primary structures within the network and are capable to perform basic operation such as creation and destruction, assigning network addresses to the sockets, establishing connections, transmission (broadcasting), receiving, etc. To measure time intervals of communication sessions the authors took advantage of functional features of contemporary motherboards of PC computers. In particular, the function of the API counter was used as it allows to readout the fast internal 64-bit counter which, in consequence, enabled measurement of time gaps with accuracy up to single microseconds. The described software performs tests of communication facilities in terms of their applicability to fast data exchange between field control modules of the control system and the CPU, whereas the entire communication is performed via Internet. Therefore the reaction time of a hypothetical field controller in respond to switchovers of the input signals or interrupt events can be measured. The communication and measurements were performed over local and national internet networks as well as for GPRS networks. Measurement results are presented in a compact form of tables that is suitable for further analysis. The presented system is able to transmit diagnostic information therefore it can be also used for integrated diagnostics of mechatronic systems as well as for location and analysis of possible failures within the in-field systems.