Here's a nice long article about delay vs rollback strategies of handling synchronization of state in real-time multiplayer games. Very interesting.
When there is no information from the remote player, delay-based netcode needs to pause and wait, as described in detail on the previous page. Rollback’s main strength is that it never waits for missing input from the opponent. Instead, rollback netcode continues to run the game normally. All inputs from the local player are processed immediately, as if it was offline. Then, when input from the remote player comes in a few frames later, rollback fixes its mistakes by correcting the past. It does this in such a clever way that the local player may not even notice a large percentage of network instability, and they can play through any remaining instances with confidence that their inputs are always handled consistently.
