[jdev] Re: help needed to implement a P2P Chat Client

Michal vorner Vaner michal.vaner at kdemail.net
Tue Aug 29 03:04:55 CDT 2006


On Mon, Aug 28, 2006 at 04:41:21PM -0700, Ravi wrote:
> 
> You have a very valid point. However these issues are not unique to P2P 
> chat. This begs the question, how do current chat clients (jabber or 
> otherwise) manage P2P audio/video transmission? If it can be done for 
> audio/video, it can be done for text.
> 
> - Ravi
> 
> P.S.: Note that this is now just for sake of discussion. As I mentioned 
> in another post, I do agree that benefits of P2P chat are questionable. 
> I will consider starting with proven technology and reconsider the 
> architecture in next version.
> 
Well, the p2p for video/audio is used because:
*) The cost of creating the session is significantly lower than the data
itself. It is some 25 packets of UDP data per second for audio in lowest
quality, as far as I know.
*) Time problems. With audio, you do not want the data to get too old.
With text message, quarter of second is just fine.
*) The amount is unrouatable by the servers, even if you had a lot.
*) There is no big problem, if some of the packets get lost. It is
easier to smuggle UDP packets trough NATs than TCP connection.

To get the smuggling of packets trough NATs (STUN), you need help from
outside - from the server. With skype, it is done by poor skype users
with public addresses. Unless you want to do something so dirty and
discouraging for people with good internet connection, you are left with
servers. Which is where you were with just routing the messages. How
much do you expect the users to write?

I guess it will not be much problem to setup a cluster of servers. With
ejabberd, I know of deployments of tens of thousands and the developers
say if you need more, just add more servers to the cluster. I do not
know, how far you can go, thought. And you gain the advantage users can
use whatever client they like, if you use unmodified XMPP.

-- 

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Michal "vorner" Vaner
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