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Game Networking 101

Vol. 2, Issue 10
January 31, 2000 


So ok, we’ve seen the mess that is the Internet, and all the pitfalls, what can we do about them as game developers?

Rats, I knew someone was going to ask that. I thought I was done, Check please. But noooo, more stuff to have to type up. Oh well.

The first thing we should do is define the difference between client/server type games and peer to peer games.

Peer to peer involves two or more games talking to each other, each running the game itself and only exchanging input data. This reduces network traffic to a minimum, but brings several other problems to the table, like coping with lost traffic. This is far more important when more than one game is running, since contention occurs over who is correct and who is not. Variance in game play can get very sticky in these situations, as each game must stay synchronized with the others. Additionally, each game must wait for the input from the others before it can simulate the next frame – remember playing DOOM and it would lock up momentarily?

Client/Server involves one machine running the game and dictating to all the clients what the state of play is and what they should be displaying. Effectively the clients become pretty much dumb terminals transmitting the user input to the server, and letting it handle almost everything. They draw the scene the server tells them to display, and play the sounds the server tells them to play. Actually, it's not quite as bad as this, as the server does on occasion tend to offload functionality onto the client, but that's the basic idea.

What I'm going to discuss has more to do with Client/Server type setups than peer to peer since almost all online type games have some degree of Client/Server architecture to them - every game has to have one client that 'hosts' the game and is considered 'correct' in the case of world event contention between peers. (Unless they don’t, in which case, you’d just get an “out of synch” error and quit.)

Ok, now on to our problem list - The TCP/IP selection is a no brainer - we don't have to discuss that anymore.

One down.

Packet bloating. This one can be tricky. Obviously a max packet size in the code is in order here to stop modem buffer overloading. We here at Raven are actually implementing a floating max packet size, for those people who are running over a local network, or that have large bandwidth available to them. When you hit a packet that breaks your buffer size, the secret is to split the data into two smaller chunks - only send in the first packet what is really necessary to be there that instant. Data like entity movements and so on. Stuff like chat messages can wait till the next packet, since no one is going to miss that being one packet late. Still, tough decisions need to be made as to what's important and what isn't, and sometimes this can make the game feel a little sluggish and unresponsive. This is where the floating packet size can be helpful, since it should remove that feeling from those with large bandwidth or running local games. Not the best solution, but one that's worth a try.

Other stuff that's worth thinking about includes tokenizing text messages. If your server is sending a lot of preset text messages, it makes more sense to have these pre-loaded on the client, and just send them a text string reference number rather than the whole string. This reduces out message traffic considerably. The same trick can be played with sending down filenames when the server asks the client to load something. For instance you can break down the file into path names, and then filenames. If you are asking for a bunch of sound files to be loaded, then only send the path once, and from then on, refer to the path as a token in the string. For instance we'll ask the client to load

"sound/weapons/death.wav". Once the client receives this string, it will store away the path as a token, and the next time we want a sound, we send "%1pain.wav" and the client knows by the %1 to go away and use that path it got first time to load this sound. Little things, but they all help.


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Credits: Illustration © 2000 Costas (Darkpath Images) and Andy, This article is © 2000 Jake Simpson. All other content is © 2000 loonyboi productions. Unauthorized reproduction is prohibited. So don't do it, or we'll give you really, really, bad lag.