Protocols for distributed real-time systems

Novel and specialized protocols will be necessary to deal with the requirements of time-constrained communication and synchronized clocks in an important area of technology, viz., the next generation of distributed real-time systems. Our research concentrates on developing distributed system protocols that realize these requirements. In this dissertation, we have proposed, analyzed and evaluated new protocols to meet these requirements. A clock synchronization protocol is used to provide support for a common system-wide time base. We have proposed and analytically evaluated a novel probabilistic algorithm for clock synchronization, that can guarantee a much lower bound on the deviation between clocks than most existing algorithms. The guarantee offered by our algorithm is however probabilistic, i.e., there is non-zero probability that the guarantee offered by our algorithm will fail to hold. The probability of invalidity of the guarantee, i.e., the probability that the deviation exceeds the guaranteed maximum deviation, can however be made extremely small by transmitting a sufficient number of messages. We have presented a detailed analysis of the protocol. Among other things, we considered three different bounds on the probability of invalidity, and showed that a bound on the probability of invalidity decreases exponentially with the number of messages. In our work on time-constrained communication, we have proposed RTLAN, a new local area network architecture for distributed real-time systems. RTLAN incorporates new communication abstractions (real-time virtual circuit, real-time data-gram) and provides new classes of connection-oriented (RTCOS) and connectionless services (RTCLS) that explicitly consider the timing requirements of messages. It employs specialized real-time communication protocols at the medium access control layer to support these services. We have developed, analyzed and evaluated a homogeneous suite of five real-time medium access control protocols based on a uniform window splitting paradigm. Performance evaluation studies by simulation show that these protocols perform well compared to idealized baseline protocols