The assumption of random node selection makes possible something that we call implicit consensus. There are multiple rounds in our protocol, each corresponding to a different block in the blockchain. In each round, a random node is somehow selected, and this node gets to propose the next block in the chain. There is no consensus algorithm for selecting the block, and no voting of any kind. The chosen node unilaterally proposes what the next block in the blockchain will be.
Narayanan, Arvind, et al. (2016). Bitcoin and Cryptocurrency Technologies. United States: Princeton Press