Telecommunications systems have been evolving from the conventional telephone network that mainly deals with voice, to the ISDN (integrated services digital net work) integrating voice, data and image. Moreover, the ATM (asynchronous trans fer mode) and optical switching technologies are being developed for the broadband ISDN which can handle the high speed video communications as well. Computer networks are also progressing from centralized TSS (time-sharing system) to dis tributed LAN (local area network) and VAN (value added network). In the research, development, design and operation of such telecommunications and computer networks, the important problems are determining the optimum con figuration and dimensions of the systems for providing a given performance or GOS (grade of service). The teletraflic theory, the basis for the performance evaluation and the dimensioning, has been studied along with the switching technology, and has developed rapidly by incorporating the recent advances in OR (operations research) and queueing theory. However, it is sometimes difficult for non-experts of teletraffic to understand and apply these theories, because they require a deep mathematical background.
