A game server (sometimes host or shard) is a server which is the authoritative source of events in a multiplayer video game. The server transmits enough data about its internal state to allow its connected clients to maintain their own accurate version of the game world for display to players. It also receives and processes player input.

Types[link]

Dedicated server[link]

Dedicated servers simulate game worlds without supporting direct input or output (except that required for administration). Players must connect to the server with separate client programs in order to see and interact with the game.^[1][2]

The foremost advantage of dedicated servers is their suitability for hosting in professional data centers, with all of the reliability and performance benefits that entails. Remote hosting also eliminates the low-latency advantage that would otherwise be held by any player who hosts and connects to a server from the same machine or local network.^[1]

However dedicated servers cost money to run, and they tend not to appear in meaningful numbers unless a game has a clan culture. They are also inefficient for games which support smaller numbers of players (such as real-time strategy games, which are often played 1v1).

Listen server[link]

Listen servers run in the same process as a game client. They otherwise function like dedicated servers, but typically have the disadvantage of having to communicate with remote players over the residential internet connection of the hosting player. Residential connections rarely support the upload requirements of games with many players; the typical limit is 16. Performance is also reduced by the simple fact that the machine running the server is also generating an output image. Furthermore, listen servers grant anyone playing on them directly a large latency advantage over other players ("host with most") and cease to exist when that player leaves the game.^[1]

But listen servers have the advantage of being essentially free and not requiring any special infrastructure or forward planning to set up, which makes them common at LAN parties where latency and bandwidth issues are not a concern. They are also common in console games.

Peer-to-Peer[link]

In the client/server model outlined elsewhere in this article, clients receive processed data from the server and display it without much thought. In the alternative "peer-to-peer" model there is no server: each "peer" instead receives the raw input streams of each other player and determines the results itself.^[3]

Peer-to-peer is generally considered obsolete for action games, but it still common in the real-time strategy genre due to its suitability for games with large numbers of tokens. Instead of constantly transmitting the positions of 1000 troops, the game can make a one-off transmission of the fact that 1000 troops are selected and that the player in command of them just issued a move order.^[3]

However, it has many disadvantages:^[3]

• It is very difficult to keep all peers synchronised. Minute differences between peers can escalate over time to game-breaking paradoxes.
• It is very difficult to support new peers joining part-way through a game.
• Each peer must communicate with all other peers, limiting the number of connected players.^[1]
• Each peer must have exactly the same version of the game (impacting modding).
• Each peer must wait for every other peer's message before simulating the next "network frame", resulting in all players experiencing the same latency as the player with the worst connection.

Customization[link]

Servers, particularly those of PC games, can generally be customized in ways that still allow unaltered clients to connect to them. These customizations can include tweaks to built-in game settings, content that is downloaded by clients when they join the game,^[4] and new code which changes the way that the server behaves.^[5]

While server customization is popular with server administrators and players, it can be at odds with developers' desire for their game to be experienced as they intended.^[6] It can also aggravate players by enabling abusive administrators to lie about what their server offers.^[7]

See also[link]

• Half-Life Dedicated Server
• Lag (online gaming)
• Matchmaking (video games)

References[link]

1. ^ ^{a b c d} Armstrong, Andrew (2009). "The Mammoth Dedicated Server Guidebook". Mammoth Media. http://www.mammothmedia.com.au/~/media/92E27A0F97F34A958D6D4B9F3CD2A64F.ashx. 
2. ^ Bernier, Yahn (2001). "Latency Compensating Methods in Client/Server In-game Protocol Design and Optimization". Valve Corporation. http://developer.valvesoftware.com/wiki/Latency_Compensating_Methods_in_Client/Server_In-game_Protocol_Design_and_Optimization. Retrieved 17 September 2011. 
3. ^ ^{a b c} Fiedler, Glenn (24 January 2010). "What every programmer needs to know about game networking". http://gafferongames.com/networking-for-game-programmers/what-every-programmer-needs-to-know-about-game-networking/. 
4. ^ "HTTP Fast Download". Steam Support. Valve Corporation. https://support.steampowered.com/kb_article.php?ref=9717-HMAP-7066. Retrieved 5 May 2012. 
5. ^ "Server Plugins". Valve Developer Community. Valve Corporation. https://developer.valvesoftware.com/wiki/Server_plugins. Retrieved 5 May 2012. 
6. ^ Bowling, Robert (21 October 2009). "Modern Warfare 2 For PC". Archived from the original on 21 October 2009. http://web.archive.org/web/20091021202340/http://www.fourzerotwo.com/?p=745. 
7. ^ Walker, Robin (12 March 2009). "And that's what ye git fer toochin that!". Team Fortress 2 Blog. Valve Corporation. http://www.teamfortress.com/post.php?id=2338.