Robustness of real-time local area network protocols

Abstract

This paper proposes a formal definition of the robustness property which, we believe, developers of future real-time local area network (LAN) protocols must aim to realize. As demonstrations of the utility of this definition, the TDMA (time division with multiple access) protocol and the carrier sense multiple access with deterministic collision resolution (CSMA/DCR) protocol are analyzed for their robustness. CSMA/DCR is one of the few major real-time bus LAN protocols, striking a good balance between the CSMA/CD protocol with weakly predictable timing behavior, and the TDMA protocol that has a tightly bounded worst-case delay but is inflexible. We show that the ordinary CSMA/DCR and other LAN protocols, which are relatively weak in regularity and predictability of shared media access patterns, are not very robust in that the protocols lose their real-time delivery properties when various types of faults occur.