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Most networked games are built on UDP that resend the game state many times to ensure a high probability of timely delivery. Desync is common and is caused by

Most networked games are built on UDP that resend the game state many times to ensure a high probability of timely delivery. Desync is common and is caused by packet loss in UDP games. It's not usually worth while to compare your state with the authoritative state, because that requires a round-trip from client->server. Instead, the server can rank each piece of the state as important (has been altered recently is a good measure of importance), and just spam out a bunch of redundant game state packets hoping some of them arrive. You can build a guaranteed delivery packet system on top of UDP, but a guarantee has to come from the client meaning you're waiting on round-trips to confirm that the states are fully in-sync. Most games (especially fast paced shooters) don't need this level of assurance, and heavy packet loss over a long period of time should just result in a disconnect for that player.

midnightclubbed 5y ago
Every networked game I've seen uses a reliable transmission layer built on top of UDP. Generally there are packets that work as you describe and are fired out to the server (and/or other players) with 'full' state (typically player position, orientation, speed and maybe a few state bytes... with orientation sent more regularly than position and speed). The remainder of packets are sent reliably. Each game packet is typically packed (and compressed) with other game packets to maximize bandwidth and acknowledgment data for the reliable packets is also compressed into the data stream. Reliable packets take very little additional bandwidth (assuming your UDP connection is not going to lose many packets in normal use). Players will pull ethernet cables for a second to force packet loss if the unreliable packets give them an advantage (ie to allow them to interpolate through a wall or to not register shot hits).

midnightclubbed 5y ago

Every networked game I've seen uses a reliable transmission layer built on top of UDP. Generally there are packets that work as you describe and are fired out to the server (and/or other players) with 'full' state (typically player position, orientation, speed and maybe a few state bytes... with orientation sent more regularly than position and speed). The remainder of packets are sent reliably. Each game packet is typically packed (and compressed) with other game packets to maximize bandwidth and acknowledgment data for the reliable packets is also compressed into the data stream. Reliable packets take very little additional bandwidth (assuming your UDP connection is not going to lose many packets in normal use). Players will pull ethernet cables for a second to force packet loss if the unreliable packets give them an advantage (ie to allow them to interpolate through a wall or to not register shot hits).