Udp server too slow?

Question

So im doing an MMO, i was progressing alot, 6 months progrramming this thing. The problem is that i was testing offline my game, today i have the brilliant idea to port foward my server and make it online, i knew it was gonna be slighty slower, but its awful! too much lag!!! the game is unplayable. Im managing my packets like so....

Player wants to move up, client send movePacket to the server, the server recieve it, move the player in the server and send the new position to all clients... Each time a monster move, the server send a the new position to all clients...

I thought i was over sending packets, but i test it just with the movement of the player... it seems to have a significant delay to recieve the packet and sending them to the client.... Im I doing this whole thing wrong?

Answer 1

Lag is always a problem with online games. While your current method is the standard way of doing things, as your finding out the lag becomes unbearable (a common problem in 1990's and early 2000's games). The best approach to take is the same approach that almost all modern games take which is do as much as you can client side and only use your authoritative server to resolve differences between predictions that clients make. Here are a some helpful ways of reducing perceived lag:

1. Client-side prediction
   For an MMO this may be all you need. The basic idea of client-side prediction is to locally figure out what to do. In your game when Player wants to move up he sends a packet that says [request:1 content:moveup] then BEFORE receiving a response from the server, the client displays Player moving up one (unless there you can already tell that such a move is invalid i.e. moving up would mean running into a wall). If your server is really slow then Player may also move right before receiving a response so your packet next packet may look like [request:2 content:moveright] at which point in time you show your player to the right. Keep in mind at this point Player has already moved up and right before the server has even confirmed that moving up is a valid move. Now if the server responds that the new player position after packet 1 should be up and the position after packet 2 should be right then all is well. However, if lets say another player steps happens to be above Player then the server may respond with the player in a new location. At this point Player will 'teleport' to wherever the server tells him he's supposed to be. This doesn't happen often but when it does happen it can be extremely noticeable (you've probably noticed it in commercial fps games).

2. Interpolation
   At this point your probably fine for a MMO game but in case it isn't (or for future reference) interpolation is your next step. Here the idea is to send more data regarding rates at which values change to help make the movement of other players smoother. This is the same concept as using a taylor series in mathematics to predict values for a function. In this case you may send position as well as velocity and maybe even acceleration data for all the entities in the game. This way the new position can be calculated as x = x + v*t + 0.5*att where t is the frame rate. Again, you show the player's predicted position before the server actually confirms that this is the correct position. When the next packet from the server comes, you'll inevitably be wrong most of the time but the more rate data you send, the less you'll be off by and thus the smaller the teleportation of other entities is.

If you want a more detailed outline of how to deal with lag in online games read the mini bible on multiplayer games: http://www.gabrielgambetta.com/fast_paced_multiplayer.html