Netcode

Netcode is a blanket term most commonly used by gamers relating to networking in online games, often referring to synchronization issues between clients and servers.

Players often blame "bad netcode" when they experience lag or reverse state transitions when synchronization between players is lost. Although these events are sometimes caused by bugs, other networking-related causes include high latency between server and client, packet loss, or network congestion. Depending on the game implementation, these issues can also be caused by non-network factors such as frame rendering time or inconsistent frame rate. Netcode is often designed to mask networking irregularities and create a synchronous and smooth gamestate across multiple users.

Netcode types

Unlike a local game where the inputs of all players are executed instantly in the same simulation or instance of the game, in an online game there are several parallel simulations (one for each player) where the inputs from their respective players are received instantly, while the inputs for the same frame from other players arrive with a certain delay (greater or lesser depending on the physical distance between the players, the quality and speed of the players' network connections, etc.). During an online match, games must receive and process players' input within a certain time for each frame (roughly 16.5 ms per frame at 60 FPS), and if a remote player's input of a particular frame (for example, of frame number 10) arrives when another one is already running (for example, in frame number 20, roughly 170 ms later), desynchronization between player simulations is produced. There are two main resolutions to this conflict implemented in modern games: delay-based and rollback-based resolution.

Delay-based

The classic solution to this problem is the use of a delay-based netcode. When the inputs of a remote player arrive late, the game delays the inputs of the local player accordingly to synchronize the two inputs and run them simultaneously.