Problem
MAC protocols in the category of "contention-based protocols with reservation mechanism" can be divided as synchronous protocols and asynchronous protocols, which means that the time on all nodes need to be and need not to be synchronous, respectively. Specifically, D-PRMA is a synchronous method, while MACA-PR is asynchronous. Explain why D-PRMA needs time synchronous among all nodes, and why MACA-PR does not need time synchronous?