Flow-Control Policies for Wireless Sequencer-Based Causal and Total Order Communication

Many embedded wireless systems can benefit from causal and totally ordered communication (CATOC) in order to achieve reliability and logical consistency at the application level. In this paper, we present a sequencer-based CATOC protocol designed to exploit the physical broadcast capability of wireless interfaces. Under ideal conditions, the propagation and delivery of an application message to the entire group costs only 2 packet transmissions, or just 1 transmission if the message originates from the sequencer. Furthermore, we propose different flow-control policies for reducing the number of collisions in case of contention, as well as to improve fairness among the members of the process group. We evaluate our implementation over an IEEE 802.15.4 network for different group sizes and application messaging rates, showing that the choice of the flow-control policy can radically affect protocol performance.