[GD-General] Online Gaming

[<ash...@ya...>]

After getting my PS2 network adaptor I've been playing SOCOM online for the past few days. Today though I put on a copy of Tony Hawk4 and was pretty surprised with how it played online. Even on what I'd consider to be laggy servers (200-250 ping) the game seemed remarkably fluent and consistent, i.e no warping players. Although I've played lots of FPS games which usually use a client/server architecture I'd never really played a fast-paced peer-to-peer game and always assumed that on anything other than LAN or fast broadband the game would suffer. Although I'm familiar with how C/S architectures work and how the effects of latency can be compensated for, I've never really given P2P much thought before in terms of how games can achieve a smooth playing experience, or even how their network update is structured. Possibilities I can think of for fast action games using P2P: a) Clients are fully deterministic and perform a lock-stepped update based on inputs from all clients. For instance all clients perform their physics update based on inputs from clients during frame 180 and obtain identical results. Problems: this means that there's a delay between input & response, even on the local client, of around half the ping time to the slowest machine. Not too good I'd imagine on a slow connection. b) All clients send their essential information (position, orientation, etc) and run their physics based on the last, or extrapolated details of other players. Problems: clients may come up with slightly different results due to extrapolated data for other players (e.g the client coliding with another vehicle). There's also the problem of non-player entities in the world, for instance a crate, which may end up with different positions on different machines if some form of correction is not performed to remove errors due to the above problem. 
There's probably other problems or solutions I've not thought of though! I'd be very interested in comments from people who've implemented P2P solutions in games aimed at the online market though, especially to do with how they handled gameworld physics and physical non-player entities. Very fascinating subject. Thanks, Andrew  



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