What causes desync in multiplayer games? [closed]

Question

A very simple question I am trying to solve my desync problems. I have looked around the net and some people say it is one thing that causes it others have different conclusions.

• Is it caused by my computer not being as good at performance of other players computers processing capabilities meaning it cant keep up with them, to give an example of this you could say my computer is a slower at reading a book than others so it is not on the same chapter as them.

• I checked my internet connection and speeds and I have a good low latency connection with high bandwidth (40+Mbps)?

• Or does it depend on the way the game programmers have built the game, in that case I cannot solve it unless they patch the game?

Myself I think it is a mixture of them all above which is making certain games (ArmA2 , Wargame EE, Planetside 2) unplayable at times.

Answer 1

(Note that this answer makes some assumptions about what you mean by "desync")

It is NOT YOUR FAULT:

"Sync Errors" occur in multiplayer games because they are attempting to run an identical simulation on multiple machines. That means that a centralized server is not running the simulation, but instead with enforced latency and a queue of all user inputs, multiple clients are running an identical simulation all at the same time. A lot of games do this because it removes the overhead of server-side simulation and upkeep, and it also makes implementing instant-replay pretty easy. Ever notice how you can't get a terminal (crashes the game entirely) sync error in games that have dedicated servers? You can just reconnect and get right back in the action.

The downside is that if either of the clients' simulation no longer matches up with the others, the simulation is undefined and cannot continue. Which version of reality is the "right one"?

Here's a few reasons that a game can go out of sync:
- Random number generation that is not properly deterministic
- Floating point representation and math that is not properly standardized
- An error in the transport of input information between the clients
- ANY case where doing the same thing twice can produce two different results (critical hits?)

Now, you'll notice that there is virtually nothing you can do about this. It is the job of the game developers to ensure that sync errors do not occur. Unfortunately this is a hard problem to solve! Company of Heroes has been out since 2006 and has gone through two expansions and numerous patches and still has sync errors. Upgrading your internet and computer can help, but in the end if the software were written well enough sync errors would never happen even with sub-par hardware.

This is a pretty good article on the subject by a developer of Supreme Commander.

Answer 2

Eric B. is perfectly right: desyncs happen because of a bad programming of the network layer in games. (Often because it was something added later and not thought through from the beginning, but not always).

However, we can list the things which can make those desync happen more or less often:

• Your computer can't keep up with the global simulation: it can be because your computer is too slow, or because your ping to the server is high. In any case, you can't exchange data fast enough with the server to keep up with the current state.

• Your connection bandwidth is insufficient: some games exchange far too much data to keep the clients in sync. If you can't send or receive enough to keep up with all the data necessary, you will desync. (Example: Magicka on launch, Torchlight 2 during the beta)

• Your connection's quality is poor, and you lose a lot of packets: if you play on wifi with a bad range, you are likely to lose packets. You will lose information the server sent, or the server won't get your changes. If the game doesn't handle this correctly, it can lead to desync (Example: Magicka on launch). Note that lost packets can happen even if you have a great connection. It can just happen anywhere between you and the server