In distributed embedded real-time system, Time Division Multiple Access (TDMA) is a widely used protocol in which each node involved in network accesses the medium in a time-triggered way. Therefore, a reliable clock synchronization is necessary in the communication layer. Maintenance of global time needs extra overhead, on the other hand, and wastes bandwidth due to preserving precise time window in TDMA. To relieve this issue in TDMA, we propose a new protocol-Node Order Protocol (NOP), which make nodes access shared medium by specified ordering to resolve contention. At the same time, communication protocol changes to event-driven way and not time-triggered, which will eliminate need for global time at protocol layer and further saturate the network bandwidth. In this paper, we first introduce design priciple of NOP protocol, including semantic of NOP protocol, error dectection and fault handling mechanism. Moreover to improve the availability of the NOP protocol, we also provide simple error recovery mechanism. Especially, we reconsider solution to alarm shower phenomenon in coupled network and make an attempt to use a more reliable method. The implementation of NOP protocol is described in detail. At last, we will do several experiments to evaluate the performance and the Qos of NOP protocol.
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