re: [GD-General] Online Gaming

[George W. <ge...@ap...>]

On Thu, 23 Jan 2003 21:42:43 +0000 (GMT), =?iso-8859-1?q?Andrew=20Sharpe?=
<ash...@ya...> wrote:
> 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 colliding 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.

SOCOM rules! ;-)

I've had several times when it looked like I missed a jump (actually started
falling down cliff or building, etc.) but then suddenly flashed to the "made
it!" position. I would definitely say it's case A (deterministic,
lock-step).

> 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 game world physics and physical non-player entities. Very fascinating
> subject. Thanks, Andrew

I'm also interested in client/server solutions. How are packets
bundled/unbundled into/out of streams? Do developers use sync or async code?
Callbacks or runloops? Do you open separate pipes for different queries or
is there one client/server stream that all transactions go thru?

Inquiring minds want to know! ;-)

Can anyone recommend any good "Programming Network Games" books?

--
Enjoy,
George Warner,
Mixed Mode Magic Fragment Scientist
Apple Developer Technical Support (DTS)