Choosing the packet size in multi-hop underwater networks

Two MAC layer protocols are considered for multi-hop underwater acoustic networks: Pure CSMA, suitably configured to perform over a long-delay channel, and the Distance-Aware Collision Avoidance Protocol (DACAP), a protocol specifically designed for collision avoidance via a distributed coordination function à la IEEE 802.11. We investigate the impact of packet size on the performance of these two protocols. A comparative analysis, conducted via ns-2 simulations, quantifies throughput efficiency, end-to-end delay and energy-per-bit consumption as functions of the packet size. The results clearly indicate the existence of an optimal packet size for each scenario. The optimal packet size depends on the protocol characteristics, on the offered load, and is heavily influenced by the bit error rate. The results also reveal performance sensitivity to the choice of the packet size for the different protocols (CSMA and DACAP), emphasizing how a wrong selection of the packet size can result in a higher cost to performance.