How Online Multiplayer Works: Game Servers, Peer-to-Peer, and Netcode

Server-Based vs Peer-to-Peer

Online games use one of two primary network architectures. Dedicated servers: The game world runs on a server operated by the developer or a hosting provider. Every player connects to that central server. Your inputs are sent to the server, which simulates the game state and sends updates back to all players. Used by: Fortnite, Call of Duty, Valorant, CS2. Peer-to-peer (P2P): One player acts as the host, and other players connect directly to that host's PC. Used by some older games and some console titles. P2P is cheaper for developers but means the host has a ping advantage and host migration can cause disconnects.

How Netcode Works

Netcode is the code that manages network synchronization. Key techniques: Client-side prediction: Your client immediately shows the result of your inputs (you move forward when you press W) without waiting for server confirmation. If the server disagrees, it sends a correction and the client snaps to the correct position. Lag compensation: Dedicated server games record the position of all players at each moment. When the server receives a late packet from you saying "I shot at position X," it rolls back to the state the world was in when you fired and checks if the hit was valid. Interpolation and extrapolation: To smooth out the positions of other players despite packet intervals, clients interpolate (show slightly delayed movement) or extrapolate (predict where they are going).

Why This Matters

Understanding netcode explains behaviors like getting shot around corners (lag compensation showing your shot as valid from your perspective in the past), rubber banding (server corrections), and desync (server and client disagreeing on positions).