[jdev] Re: Question about Proxy65 support Voice Chat

Justin Karneges justin-keyword-jabber.093179 at affinix.com
Thu Apr 21 04:16:27 CDT 2005

On Thursday 21 April 2005 02:04 am, Richard Dobson wrote:
> > Voice and audio is not like that. You will need to transfer it reliably.
> >
> > TCP is what SIP/SDP has selected (there's another protocol at that layer
> > too that's been drafted for use). Their model of getting around NATs and
> > firewalls is also a lot like proxy65 in that a third party server is
> > used.
> Are you sure? I thought they used RTP, and I was under the impression RTP
> uses UDP not TCP, as TCP is not appropriate for real time data (audio) due
> to various reasons that are outlined in the information about RTP.

You are correct.  "TCP is what SIP/SDP has selected" is a misleading 
statement.  Even though SIP may be able to use TCP, the voice data doesn't 
actually go over SIP itself.  It goes over a separate RTP channel, and more 
often than not this is UDP.


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