Desync is the bane of online multiplayer for certain games.
Desync is the inability to stay in synchronization with other players which results in a loss of proper input recognition. This can include, but not limited to delays between keyboard inputs and corresponding actions on screen, turning around when you meant to strafe, running forward then blinking back five feet, or swinging your weapon without any effect.
Given that some match-ups have experienced up to six minute disconnection periods it’s no wonder this can lead to frustration from both players stuck waiting for desynchronization versus those who simply want a good game. In order to combat this problem many games are switching over increasingly towards peer-to-peer networking as opposed to client/server networking that has been used by the majority of games thus far.
Desync is closely related to lag, but not exactly one in the same. Lag occurs when there’s a high latency between your client and the host which results in an impaired online gaming experience where actions are delayed or skipped entirely. The delay can vary from milliseconds to minutes depending on your internet connection speed.
Desyncs can occur for many reasons, but will usually go away by itself if you simply wait long enough. Unfortunately this isn’t always the case for every game, and desync doesn’t happen due to one singular reason either. Sometimes placing or receiving damage is what causes it (for melee/ranged combat), while other times it’s the result of your client losing track of another player (for ranged/magic combat).
Desync isn’t exclusive to any particular genre, and can often occur in games that don’t even use a peer-to-peer networking or latency compensation. This goes for many strategy games like Starcraft 2, World of Warcraft, and Diablo 3.
Desync is also not exclusive to online gaming either, as it can sometimes occur in local co-op games too for similar reasons. Beyond Good & Evil HD had a number of players complaining about desyncs ruining their experience with the game’s drop-in/drop-out co-op mode.