  The connected and autonomous systems (CAS) and auto-driving era is coming
into our life. To support CAS applications such as AI-driven decision-making
and blockchain-based smart data management platform, data and message
exchange/dissemination is a fundamental element. The distributed message
broadcast and forward protocols in CAS, such as vehicular ad hoc networks
(VANET), can suffer from significant message loss and uncertain transmission
delay, and faulty nodes might disseminate fake messages to confuse the network.
Therefore, the consensus mechanism is essential in CAS with distributed
structure to guaranteed correct nodes agree on the same parameter and reach
consistency. However, due to the wireless nature of CAS, traditional consensus
cannot be directly deployed. This article reviews several existing consensus
mechanisms, including average/maximum/minimum estimation consensus mechanisms
that apply on quantity, Byzantine fault tolerance consensus for request, state
machine replication (SMR) and blockchain, as well as their implementations in
CAS. To deploy wireless-adapted consensus, we propose a Directed Acyclic Graph
(DAG)-based message structure to build a non-equivocation data dissemination
protocol for CAS, which has resilience against message loss and unpredictable
forwarding latency. Finally, we enhance this protocol by developing a
two-dimension DAG-based strategy to achieve partial order for blockchain and
total order for the distributed service model SMR.
