An overload cycle analysis of generalized bandwidth balancing for DQDB

A novel state-space approach is used to characterize the overload cycle behavior of a generalized bandwidth balancing (BWB) scheme for the distributed queue dual bus (DQDB) multiple access procedure. The author exploits the fact that each node and the bus can be modeled by a finite state machine and will have cycles in the state diagram. The cycles of interest are referred to as overload cycles and result when one or more nodes are simultaneously trying to access the bus as quickly as possible. The author determines the overload cycle invariants imposed by BWB and generalizes BWB to be any integral relationship between used and skipped empty segments. It is shown that the ordinary access-based priorities cannot work, without some additional cycle invariants, in a system employing bandwidth balancing since it is impossible to preclude service to an upstream low priority mode and generalized BWB is suggested as an alternative method for obtaining rate-based priority grades of service