Bandwidth allocation for real-time communication with LTPB protocol

The LTPB (Linear Token Passing Bus) protocol is a timed token protocol which has been designed by the SAE (Society of Automotive Engineers) as a LAN standard (AS4074) to support real-time communication in mission-critical systems. This paper studies the real-time characteristics with LTPB network. A bandwidth allocation scheme is proposed based on the traffic load balance of each node. The necessary and sufficient conditions of guaranteeing message deadlines under the allocation scheme has been derived, which can be used to predict whether there is any missed message deadline for any given message set. The bound of the Worst Case Achievable Utilization for the scheme has also been derived and formally proved, which can be used in system design period when exact knowledge of the message set is not available.