Hi all, I am designing the network protocol for a 3D multiplayer space combat game. With regards to movement, client to server, we are sending out event-based information*. But server to client, should the server: a/ calculate the new game state (based upon the events input) and send out a new state-dump^ to every player? or... b/ relay the event information to every player instead? (optionally with an intermittent state-dump, to re-sync, in case the engine isn't as deterministic as we'd like :)) What are the pros and cons to each? Every networking article I've read chooses option B. Why? Does sending out complete state-dumps of every player, to every player, use less bandwidth than "just" relaying their input events? *(left roll, right yaw, etc.) ^(playerID, position, orientation, velocity, etc.)

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Original post by Viktor This way the server can enforce the rules. (a client might choose not to process an input from another player, but if it gets a state update then all it can do is update it's own state)

So with option a, the server can enforce the rules better? How? A (presumably hacked) client can ignore a state dump just as easy as an input event, and the real game-state will always be protected on the server anyway.

For a fast game with relatively little state information (eg, an FPS), sending out a state dump, or as Viktor said, a differential state dump, is probably better than sending out an event list, because state-dumps don't require a reliable connection: If a client misses a state message, then it will only be out of sync till the next state arrives, which likely won't be very long (and good client-side prediction can help to mask the effect).
For a game like an FPS, a state-dump can be kept quite small, likely no larger than a set of events (especially since events will occur at a high frequency in a fast action game), so there is little advantage in using an event-based system.

For a slower game with more state information (eg, an RTS), a state-dump would be far too large, so a deterministic engine, and reliable event-sending mechanism must be used.

John B