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In multiplayer online video games, ping refers to the network latency between a player's computer, called a client, and the game server (or another client). This could be reported quantitatively as an averaged time in milliseconds, or qualitatively as low ping or high ping. This usage is common with players of a variety of first-person shooter and real-time strategy games. Having a low ping is always desirable because lower latency provides smoother gameplay by allowing more frequent updates of game data.
In this sense, ping is conflated with lag – one may "lag out" due to unacceptably high ping. Servers will often disconnect a client if the connection is too bad and it poses a detriment to others' gameplay; or, clients will often mandate disconnection if their ping is too high and they can infer their user is not going to have an enjoyable experience because of network complications. However, this doesn't mean that a high ping causes lag. The high ping is the result of the lag. In theory, there can be more reasons of having a high ping (for example, you are transmitting data over a very, very long distance), but most servers of commercial games are associating a high ping with network lag directly.
The method used by the game programmers to determine ping times will often not use the traditional ICMP echo request and reply packets, but instead piggyback the functionality onto existing game data packets (often using UDP).
Some factors that might affect one's ping include: network protocol engineering, internet connection speed, quality of the internet service provider and the configuration of firewalls. Ping is also affected by geographical locations. For instance if someone is in China playing a server from America, the distance between the two are farther and it takes a longer time for the data to be sent to China. The amount of packet-switching and network hardware in between the two hosts is often more significant. For instance, wireless network interface cards must modulate digital signals into radio signals, which is often more costly than the time it takes an electrical signal to traverse a reasonable span of cable.
In most cases, games seem to give unfair advantage to high-ping users, as in some implementations of the Half-Life network protocol and game engine. In these games, the player ailed by the higher ping skips around, making it hard to judge where the character is exactly, and thus more elusive to target. For this reason, many servers automatically remove players with higher than average ping - with thresholds going as low as 130 milliseconds.
In more modern multiplayer online video games implementations, the server keeps track of where the user's avatar is, so having a high latency will always be the user's peril.
In GunZ Edit
High-ping players will often be kicked, as they often cause frustration through "lag shields" and may experience "Agent Error", causing them to be unable to interact with other players on the field. As of 29 April 2009, ijji servers show players logging in their ping through cell phone-like bars before they connect.