Dynamic synchronous bandwidth allocation scheme for hard real-time communication in FDDI networks

In a distributed system for hard real-time applications, communication by message exchange between tasks residing on different nodes must happen in bounded time. Due to its timed token MAC protocol, FDDI provides a suitable network structure for these systems. The paper proposes a synchronous bandwidth allocation (SBA) scheme for deadline guarantees of synchronous messages with arbitrary deadlines in an FDDI network. The major amount of information used by this scheme in calculating the synchronous bandwidth of a node is locally available to the node involved. The limited use of global data makes this scheme suitable for dynamic environments. In this study, a distributed management protocol has also been designed to update synchronous bandwidths of nodes dynamically when the data load in the network changes. It is shown that the scheme performs better than other previously published ´pure´ local schemes.