32 High Perfonnance ATM Tenninals: Design and Evaluation George E. Konstantoulakis and George I. Stassinopoulos Division of Computer Science, National Technical University of Athens Zographou, GR-157 73 Athens, Greece This paper intends to show that even low end tenninals can, under given implementation guidelines, become hosts of multimedia applications over ATM based B-ISDN. The main line of thought is that the tenninal has to be seen as an Interworking Unit between its peripheral devices (disks, etc.) and the high bandwidth network. This view enables to jointly address and process in a "centralized" manner, layered protocol stack(s) used for accessing the network and the peripheral devices. In particular we give directions to eliminate unnecessary block transfers in memory and explain why extensive hardware implementation of the ATM protocol stack is not required to achieve high performance. KeyWords Interworking Unit, ATM Networks, Broadband Tenninal, Multimedia Tenninal, Layered Protocol Stack, Cell and Packet Hardware Interface, Protocol Control Information, PC Adapter, File Transfer, Video Transfer. Acknowledgment The authors would like to acknowledge the support received within the framework of RACE projects R1022 "Technology for ATD" and R2061 "Exploit" by the European Union, while perfonning this research. 1. INTRODUCTION Broadband integrated networks are by now based on the ATM (Asynchronous Transfer Mode) principle [1, 2] and irrespective of controversies about the eventual large scale applicability of this concept, two main lines of products are currently available. On one hand, network administrations promote ATM based crossconnects covering the need of remote LANs (mainly Ethernet) interconnection. This requires newly designed bridges but does not concern new tenninals. On the other hand we have the emergence of several ATM based LANs. These are ATM switches with appropriate tenninals attached in a star architecture. Here we have the need of high perfonnance tenninals, being able to support a communication related stack for up to 155 Mbit/sec ATM rate. At the same time these must provide the processing power needed for commensurably fast and complicated multimedia applications. D. D. Kouvatsos (ed.), Performance Modelling and Evaluation of ATM Networks © Springer Science+Business Media Dordrecht 1995