   three question on server side
  I am writing a tank game1. when to check the client input?should client input get check by engine as long as the input received?2. what does the engine should provide? just collision checking or both checking and compute the movement?eg: if client to move tank to (x,y) and send this to server. what info should server reply? 3. when should i send the reply?should send immediately after checking or should I send all together with certain intervals?what is on my mind nownow in my game client side I have timer (30) to produce each frame. no server side i have same timer (30) I will keep all the input during the 30 millisencondand check them all together when time out and send the reply all together after checking.is that all right?  I feel it is not right......   
  no one can answer the question?????   ;  I'm pretty sure the Forum FAQ answers your questions. There is no one, right answer -- the answer to most of these questions depends on what your particular situation and needs are, because there are many ways to do networked gaming, each with its own benefits and draw-backs.;  again, look at Gaffer's article on networked physics. That's the sort of things you need to do for client-side prediction and full server-authority.for lag compensation (meaning, doing more accurate client hit prediction), looky here and here.