MMO Server functionality in Unity3D [closed]

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I've created a multiplayer server for Unity that works like this:

• Every client/player connects to the server and says 'hi'.
• Server accepts the player and adds him to the players online list.
• Every client start sending his position.
• Server listens for client's positions and X times per second sends them to all other players online.
  • This is made by one bucle on all online players, so the server is configured to send say 10 times per second the updated positions to all the players.
• Every client listens the server for other players position. When the server says "this player just said he's there", the client moves him there.

With this basic system, I can create a multiplayer game with Unity easily (already did it). But what if there's more than a couple of thousand players online? Then, say that every player sends his position to the server about 10times/sec. And the server has to send those position to all players around, say 100m. So, the server would run a loop for all online players (2000) comparing his position with the all 1999 players and if it's less than a 100m, send the position to the player. Or, maybe better, save all the players updated position in one array and send it to the player. (Only one message every 10s to the player should be better than hundreds, right? Anyway, the loop has to go through 2000*1999 10 times per sec, that could be painful..

I want to use Unity3d as client, I don't want to hold any physics on the server because using the unity's physics engine is good/fast/easy to work with. And I think it could be enough, maybe do some anti-cheating checking on the server-side just to get rid of badplayers.

Now, the questions :)

• How does a proper mmo server work? Does every player send its position to the server X times per second and it goes through that HEAVY loop and sends his position to all players around? what about performance?

• I would implement a prediction system for the next move and interpolate the current position wit the updated one received from the server. is it right?

• If I have to detect player collisions with each other or with objects (bullets and more) would you do it on the client-side? or implement a players-player & player-object collision detection system in the server side and do it in the big loop?

• If the player moves is with the keyboard so it doesn't have just a single position to go, how would you send the position to the server, like 10times per second and interpolate the position received by other players to create a smooth movement?

• If the movement of the players is by setting force physics to them, like when you go forwards it's because there's a strength pushing you, how would you transmit this information to the other clients? Send just the position to the server and it sends it to the other players? But then, the physics would look weird... The plan b) I thought of is to send the force used to the server and every clients applies the force received by the server to all the players around them, physics here would look awesome but maybe there's a latency problem... Would it be good to use this system and send the exact position every X time? say .5s?

Well, I think this is all! I hope this post can be useful for other indies!

Answer 1

I won't try to answer all your questions, sorry. It would be too long answer. Seems like you need to read a lot of stuff about game physics.

Shortly, if you have large number of online players you need to start thinking about server cluster and scaling. There're two main approaches:

1. Instances: you have multiple copies of your virtual world/map each handled by separate physical hardware with a hard limit of maximum number of players. Then you start reading about matchmaking.

2. "Shared universe": split your world to sectors each handled by separated physical hardware. Much more challenging to implement. Can support seamless world.

You can find tons of useful info on www.gamedev.net.