The hardest part is that most game engines are not designed to be networked in this way. Find an open source physics engine that natively supports teleportation, easing and prediction, they're not there. UE4 is the first engine I've used that seems to have a very nice multiplayer API, and it's only been out for indie developers for a couple of months.
So the hard part is not devising the networked scheme, it's building a whole game engine (or thoroughly modding one) afterwards, at least in my experience.
I was working on a multiplayer racing game project (like GTA2), and my approach was to run 2 physics engines in parallel. One physics engine would always be authoritive, and be in sync with the server, but because of the lag would always be a frame or two (or more) behind. The other would be working on predicting what is going to happen. Every frame snapping back to the authority, and then applying the (predicted and user) inputs over that.
The actual position the user would see would be an averaged position between the current predicted position, and its previous predicted position (to prevent too much jitter/snapback).
If you've got a better scheme to do networked physics I'm all ears :)
So the hard part is not devising the networked scheme, it's building a whole game engine (or thoroughly modding one) afterwards, at least in my experience.
I was working on a multiplayer racing game project (like GTA2), and my approach was to run 2 physics engines in parallel. One physics engine would always be authoritive, and be in sync with the server, but because of the lag would always be a frame or two (or more) behind. The other would be working on predicting what is going to happen. Every frame snapping back to the authority, and then applying the (predicted and user) inputs over that.
The actual position the user would see would be an averaged position between the current predicted position, and its previous predicted position (to prevent too much jitter/snapback).
If you've got a better scheme to do networked physics I'm all ears :)