The details vary, of course. Typically it's any gameplay-related commands the player gives. You avoid the timing problem by having the client timestamp the pa

The details vary, of course. Typically it's any gameplay-related commands the player gives. You avoid the timing problem by having the client timestamp the packets. Time on the server side is quantized into "ticks", which are basically frames of game state that are independent from the clients' framerate. Or at least, this is how Source engine does it.