FlexTDMA for delay-stable communications in asynchronous industrial control networks

To support closed industrial control networks we consider constant end-to-end delay with minimal delay-jitter support in an asynchronous network. The Rate Constrained Static Priority rate-jitter (RCSP-RJ) minimizes jitter while not providing full restoration of traffic at each switch. RCSP-delay-jitter (-DJ) provides jitter free network communication but requires a means of time coordination between switches. We introduce FlexTDMA that allows nearly constant delay bounds with minimal delay-jitter in an asynchronous network. FlexTDMA uses a token bucket to restore the arrival envelope of each flow. This eliminates delay-jitter, simplifies analysis of the network and avoids cyclic dependent issues in network analysis. A network of FlexTDMA switches operate asynchronously and offer nearly constant delay and minimal delay-jitter. FlexTDMA adapts the functional characteristics of RCSP-RJ while providing the performance characteristics of RCSP-DJ, through the use of periodic baselining (transmission at maximal delay bound) of each flow at each switch. When a flow has been baselined the receiving switch establishes a reserved time slot in which the next frame arrival is expected (thus the term flexible TDMA). The value of a baseline event degrades relative to switch clock drift rates. Infrequent baseline collisions cause delay-jitter, and baseline transmission opportunities (TO) can be scheduled thereby minimizing the probability of alignment.