Periodic communication support in multiple access networks exploiting token with timer

Abstract

Timed token medium access protocols axe widely adopted in real-time multiple access networks because of bounded access time. However, timed token protocols inadequately provide periodic communication 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 bandwidth 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 allocated time, the residual time is allocated to other nodes for non-periodic service using a timer which contains the unused time value and is appended to the token. This algorithm can always guarantee transmission of messages before their deadlines when network utilization is less than 50%.