Ask HN : How does time synchronization works?

I remember seeing a proof that when there is an systematic asymmetry in the network latency it is impossible to guarantee synchronisation.

It practice, however, it is reasonable to assume that latencies are randomly distributed and are largely the same in each direction. Under those assumptions it's fairly simple to come up with strategies that mostly work.

The real difficulty is finding an optimal or near-optimal strategy.

However, to answer your original question, it is provably impossible when the conditions are unknown and are allowed to be pessimal.

I think you ought to check out NTP.

http://en.wikipedia.org/wiki/Network_Time_Protocol

Check out: http://en.wikipedia.org/wiki/Marzullo%27s_algorithm