"We present three conservative synchronization mechanisms for parallel DEVS and Cell-DEVS. The protocols are based on the classical Chandy-Misra-Bryant null message mechanism with deadlock avoidance. Our protocols provide a novel DEVS-based conservative approach that is deadlockfree, and extracts the lookahead information from the model’s specification. The protocols are integrated into the CD++ simulation toolkit, providing a conservative simulator (named CCD++) for running large-scale DEVS and CellDEVS models in parallel and distributed fashion. We provide a comparative study of these protocols by investigating different performance metrics including: total execution time, blocked time, memory consumption, total number of positive and null event, as well as null message ratio, showing how CCD++ provides considerable speedups, and its ability for simulating large DEVS-based models."--From the paper.