I was writing a real-time multiplayer game a couple years ago. The netcode was written so that players only send their inputs along with a timestamp (The "time

I was writing a real-time multiplayer game a couple years ago. The netcode was written so that players only send their inputs along with a timestamp (The "timestamp" actually being a frame counter). The server would then relay those inputs with the timestamp to other players. The client maintains snapshots of the game state and would then re-run the game logic from that timestamp given the new input. I handled clients falling behind by making the server reject any inputs that were more than 500ms (Really, 30 frames) behind the current time. The server would send a message to the client that essentially said "You're lagging, here's the current frame counter and current state of the game" Granted, this approach really only worked for my game because the entire game state could be squished to ~300 bytes. But it had the added benefit that it prevented players from cheating using a lag switch. They couldn't have a malicious client that sat and listened to what other players were doing and then send a bunch of back-dated inputs to put itself in an advantageous position.