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Sergey Ignatchenko

CMB/LBTS protocol for time sync in MMOs?

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In another book (http://www.amazon.com/Massively-Multiplayer-Development-Charles-River/dp/1584503904) they're arguing for using CMP (Chandy/Misra/Bryant) and LBTS (Lower-Bound-Time-Stamp) time-sync protocols to sync different parts of the same seamless world. On the other hand, CMP/LBTS seem to be of block-until-the-slowest-one-reacts nature, so I have my doubts about using them for games (beyond non-real-time simulations where they're used to guarantee correctness). 

 

Has anybody heard about these algos used in MMOs?

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They, or their moral equivalent, are used in HLA type simulations, and in RTS games where 100% determinisim is needed.
Some company about five or ten years ago thought that HLA would TOTALLY let them rule the MMO space ... never saw a game released and they're not around, so I suppose that didn't work out.

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Thanks!

 

Some company about five or ten years ago thought that HLA would TOTALLY let them rule the MMO space ...

 

These-guys-writing-about-it-in-the-book are from Modelbenders, and the book is 2005, so it may be the same thing. And  of course, they're missing one simple thing: applicability of whatever-is-done-in-one-field to another-related-but-different-field is not guaranteed at all...

 

BTW, about these books "Massively Multiplayer Game Development" and "Massively Multiplayer Game Development 2" - they're soooo weird mix of Really Good Stuff and utterly inapplicable things (these things tend to read smoothly, but in the first 30 seconds after I lift my eyes from the text and start thinking, it becomes obvious that they cannot work in the game environment at least the way they're described...)

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Those books are like the AI Wisdom or Game Programming Gems books in that they're a collection of different viewpoints and approaches. Some are more mainstream than others. :)

 

In theory seamless worlds have consistency problems that can be overcome with these methods that are designed to allow complex simulations to proceed accurately and reliably. In practice game developers do not need to care much about most of these issues and they have workarounds for the rest. (eg. anything involving money or very important data can be routed through a single server).

 

Having said that, I don't think that "block-until-the-slowest-one-reacts" is a problem. The latency between your servers is likely to be an order of magnitude lower than the latency between your server and your players so you have quite a bit of spare time to resolve these issues.

 

Interestingly, Improbable (https://improbable.io/) are the latest people to jump in thinking that since they've 'solved' distributed physics simulations they have therefore solved online games, probably not understanding (due to their academic rather than gaming background) that the main problems MMOs face lie elsewhere and that seamlessness is a 'nice to have' feature rather than a fundamental roadblock.

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