The telecommunications hardware and software systems used in CMEA (Council of Mutual Economic Assistance) countries and Yugoslavia are a most complex field of investigation. For this reason in this study the following approach has been adopted: Rather than collecting and presenting all CMEA telecommunications hardware and software systems in a directory type of form, which would neither be complete nor fully up to date (even at the time of data collection), a general analysis is given, with sufficient detailed information to make it useful. During the analysis we will discuss in depth the different classes of telecommunications hardware and software systems, their past, present, and potential future. 

In order to do this, the analysis has to include all major levels of the International Standardization Organization's Open System Interconnection (ISO/OSI) Reference Model--and this is the way we handle the telecommunications hardware and software systems of the CMEA countries and of Yugoslavia.