Almost) No Cost Clock Synchronization

We show how synchronized clocks can be realized in a distributed system as a byproduct of a common communication paradigm where processors periodically perform broadcasts. Our approach decouples the precision concern-limiting how much correct clocks can differ from each other-and the accuracy concern-limiting how much any correct clock can differ from real time-of clock synchronization. Given a system that guarantees only precision, we develop a protocol whereby high accuracy can be achieved on demand. In this manner, the ``lazy'''' protocol we obtain incurs the cost of high accuracy only when needed while keeping the basic synchronization procedure extremely simple and cheap.