Periodic Communication Support in Multiple Access Networks Exploiting Token with Timer

Abstract. Timed token medium access protocols are widely adopted in real-time multiple access networks because of bounded access time. However, timed token protocols inadequately provide periodic commu-nication service, although this is crucial for hard real-time systems. We propose an algorithm to guarantee periodic communication service on a timed token protocol network. In this algorithm, we allocate band-width to each node so that the summation of each bandwidth allocation is the Target Token Rotation Time (TTRT). Upon receiving the token, a node consumes, at most, pre-allocated time for message transmission, and then passes it to the next node. If the node cannot consume the allo-cated time, the residual time is allocated to other nodes for non-periodic service using a timer which contains the unused time value and is ap-pended to the token. This algorithm can always guarantee transmission of messages before their deadlines when network utilization is less than 50%.