Desync

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Desync, or Peer Desynchronization, is a common networking problem caused by extreme latency in clients who are communicating to each other.

[edit] Overview

It is of particular annoyance in networked gaming when the players are not in sync with each other, giving a disadvantage to a player "behind" others.

Desync is closely related to chaos theory(?). As a game tries to reduce its bandwidth requirements, it will, instead of transmitting the entire gamestate all the time, transmit only things that change. Occasionally, taken one step further; only transmitting the things that don't change deterministically. The idea is that if both computers do the same operations on the same set of data, they will end up with the same set of data. When this idea breaks, it's called desync.

In a first person shooter, if one player shoots another, and hits on his own computer, but on another computer the target has moved differently (e.g. due to lag) the game may end up desynced with one player dead on one computer and alive on another. Usually, this is solved by server arbitration - the game server determines, based on its data, if the target got hit, and the clients continually override their own 'decisions' with those of the server. Some games also use a resynchronization process when there is too much desync, transferring the gamestate of one computer to all of them (usually pausing the game in the meanwhile). Some games stop the game. (e.g. Joint Task Force up to at least v1.1)

[edit] Desync as an Exploit

Desynchronisation is often used by player classes of the characters 'Paladins' in Diablo 2 Lord of Destruction Player vs. Player combat. The players will deliberatly exploit a skill system glitch which allows the player to couple the passive skill Vigor with the Active skill Charge. With the passive skill Vigor enabled, the character's movement speed is greatly increased. Using the active combat skill Charge (which allows the character to dash at high speeds and attack a target when colliding with them) at the same time as Vigor allows the player to move so fast that game server cannot display their location to the other players, meaning that when the desynchronised player does collide with the victim, from the victim's point of view, and any other players connected to the server who can see the player and the victim, the player's character will seemingly appear from nowhere right next to the victim and begin attacking them.

This issue can also be exploited by using only the Charge skill, without adding Vigor.