GGPO

Created in 2009, the GGPO networking SDK pioneered the use of rollback networking in peer-to-peer games. It's designed specifically to hide network latency in fast paced, twitch style games which require very precise inputs and frame perfect execution.

Traditional techniques account for network transmission time by adding delay to a players input, resulting in a sluggish, laggy game-feel. Rollback networking uses input prediction and speculative execution to send player inputs to the game immediately, providing the illusion of a zero-latency network. Using rollback, the same timings, reactions visual and audio queues, and muscle memory your players build up playing offline translate directly online. The GGPO networking SDK is designed to make incorporating rollback networking into new and existing games as easy as possible.

How Does It Work? Rollback networking is designed to be integrated into a fully deterministic peer-to-peer engine. With full determinism, the game is guaranteed to play out the same way on all players computers if we simply feed them the same inputs. One way to achieve this is to exchange inputs for all players over the network, only execution a frame of gameplay logic when all players have received all the inputs from their peers. This often results in sluggish, unresponsive gameplay. The longer it takes to get inputs over the network, the slower the game becomes.

In rollback networking, game logic is allowed to proceed with just the inputs from the local player. If the remote inputs have not yet arrived when it's time to execute a frame, the networking code will predict what it expects the remote players to do based on previously seen inputs. Since there's no waiting, the game feels just as responsive as it does offline. When those inputs finally arrive over the network, they can be compared to the ones that were predicted earlier.