DESIGN AND PERFORMANCE EVALUATION OF REAL-TIME COMMUNICATION ARCHITECTURES

There have been proposals for real time communication architectures which use acknowledged LLC services (LLC type 3) and which consist only of physical, data link and application layers. Some proposals based on the token bus (like MAP) impose the ''immediate response option'' instead of the ''requests with no response service'' of the MAC-sublayer. Simple analysis shows that in many cases the use of this option leads to a reduction in performance of the network. For an in-depth analysis of the delay characteristics and to demonstrate the feasibility of a reduced architecture, a pilot implementation based on the token bus was carried out in the author's laboratory. In this paper, the theoretical and measurement results of this work are reported, pointing out that employing the immediate response option in all situations within the intended field of application leads to greater delays. Finally, problems such as the mapping of the application services-manufacturing message standard (MMS)-onto LLC services are discussed.