Client-server Action Synchronisation

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@all the silly crap about D3 and etc.

Save yourself some time and just ignore people

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@First Post

Holy crap that was a good read. Now I know why the AI is so derpy and odd when it desyncs xD, now that I know how it works I'm not even scurred.

Okay I am no expert or network management master, especially the mass transmit of data streaming all over the world in a complex calculated driven game like PoE.

However I am creative and intuitive when it comes to problem solving, and I love this game so its only right that I throw out ideas for the cause.

Okay so the system is action prediction, I'm not going to debate whether to change that system or not. I want to improve that system. I have some simple ideas to perfect and emulate the zero lag experience every gamer enjoys.

The two main points to address:

Enemy AI


Prediction vs Pre-Calculation


Not Important but just wondering

Zell_Naga, you have to keep in mind that they don't want anything in the game to be exploitable by bots and other means of automation. They also don't want information about what will spawn/drop to be made obvious in advance as users could likely observe and manipulate what item will spawn with such information made available in advance.

I'm no master coder, hacker, or know it all, So If any of this is wrong I'm sure someone will correct me, I'm just not knowledgeable enough about how PoE functions exactly.

Before any one actually reads this,

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Nicholas_Steel wrote:

Zell_Naga, you have to keep in mind that they don't want anything in the game to be exploitable by bots and other means of automation. They also don't want information about what will spawn/drop to be made obvious in advance as users could likely observe and manipulate what item will spawn with such information made available in advance.

Which is why these advanced calculations would be done by PoE-GGG servers

The problem is, could the information from the server to client be processed efficiently to mitigate lag? For example the lag you experience upon killing an enemy and loot dropping would be replaced with lag upon triggering the pre-calculations (Trigger="monster has 20% life" lets say) Without an additional mechanism or method for smooth data and fast processing, the lag would literally be moved to right before the monster was killed, in which time the monster could kill you and it would be very uncool. The trigger could then be something else like, "monster comes on screen", but this would cause excess and unnecessary calculations. Thats what I mean by, "if flawlessly crafted", it is difficult to do. Most developers would take shortcuts but I believe GGG can do it!

Also I might add I focused completely on pre-calculated item drops, but imagine trying to do this for all calculations that add to desync, lag, etc. Its a huge mountain to climb but I set the bar high on purpose.

@Naga and Steel: I'd just like to point out that "client performs calculation" and "server performs calculation" are not mutually exclusive scenarios. Thus, it is not true that either the client must wait on the server, or the server must trust the client. There is a third option: the server and the client attempt to separately draw matching conclusions without one completely and always relying on the other. I grant that this third option opens up issues of its own, most involving how to resolve mismatches between client and server when any correction the server sends will be effected by latency and thus attempting to correct a past, rather than present, version of events. However, it is vitally important to realize that, as a matter of practical reality, Path of Exile is currently in this third category. Sometimes it seems that the developers' view of their own netcode does not fully recognize this intractable truth.

Yeah I figure their intentionally designing the client to not reliably predict monster behaviour specifically to impede bots/automation. I mean what the client predicts, is slightly wrong and this is an intentional problem to counteract predictability that automation software can take advantage of.

If the client uses Logic X and the server uses Logic Y, automation software and other cheat software will only be able to operate off of Logic X even though Logic Y takes precedent.

There will always be some desync with this approach.

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Nicholas_Steel wrote:

Yeah I figure their intentionally designing the client to not reliably predict monster behaviour specifically to impede bots/automation. I mean what the client predicts, is slightly wrong and this is an intentional problem to counteract predictability that automation software can take advantage of.

If the client uses Logic X and the server uses Logic Y, automation software and other cheat software will only be able to operate off of Logic X even though Logic Y takes precedent.

There will always be some desync with this approach.

With such a system, why make predictions at all?

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MortalKombat3 wrote:

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Nicholas_Steel wrote:

Yeah I figure their intentionally designing the client to not reliably predict monster behaviour specifically to impede bots/automation. I mean what the client predicts, is slightly wrong and this is an intentional problem to counteract predictability that automation software can take advantage of.

If the client uses Logic X and the server uses Logic Y, automation software and other cheat software will only be able to operate off of Logic X even though Logic Y takes precedent.

There will always be some desync with this approach.

With such a system, why make predictions at all?

To clarify things using a somewhat simplified model of what goes on in a system like PoE's, the client doesn't make "predictions", it displays what it thinks is going on in between sending info about the actions performed by the user to the server and receiving info about the canonical current game state. Since the server's info is always considered to be correct, the client needs to reset what it thinks is happening to what actually is happening -- sometimes the difference is large enough that it's noticeable, sometimes negatively so.

It's unlikely that the methods used by the client to calculate what it thinks is going on differ from the methods used by the server in any significant manner in terms of algorithms used.

It's also worth noting that while the noticeable effects sometimes seem to happen frequently in terms of us noticing them, they likely happen very infrequently in terms of how often this "send actions, display what should be happening while waiting for response, receive what has happened, update state / display to reflect response, repeat" cycle occurs.

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exhortatory wrote:

To clarify things using a somewhat simplified model of what goes on in a system like PoE's, the client doesn't make "predictions", it displays what it thinks is going on in between sending info about the actions performed by the user to the server and receiving info about the canonical current game state.

predictions = guesses about what is going to happen before you receive information on what happened

Your argument is invalid.

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ScrotieMcB wrote:

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exhortatory wrote:

To clarify things using a somewhat simplified model of what goes on in a system like PoE's, the client doesn't make "predictions", it displays what it thinks is going on in between sending info about the actions performed by the user to the server and receiving info about the canonical current game state.

predictions = guesses about what is going to happen before you receive information on what happened

Your argument is invalid.

The client isn't guessing at what it thinks the server is going to say happened / is happening. It's showing what is happening as far as it knows, and likely using the same methods of calculation as the server is, and then correcting itself if / when it receives data to the contrary.

The client knows what you are doing, and what's happening in the game. It just always assumes that it must have been wrong when told so from on high.

It's a bit of a subtle distinction, but it isn't prediction in the manner talked about in the post I was referencing, nor is it prediction in the senses relevant to programming or understanding what is happening in a program. It would be strictly prediction if the client was unable of knowing the methods by which the state coming back to it was calculated. Since both the client and the server are written by GGG, this is not the case.

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exhortatory wrote:

It would be strictly prediction if the client was unable of knowing the methods by which the state coming back to it was calculated.

What's the difference, again?