[Serusers] STUN and symmetric nat again

[Nils Ohlmeier]

You are right. The UA of user B needs to support symmetric RTP. Their is also 
an extension for SDP called co-media which allows you to explicitly tell the 
other side "I will start the media stream" or "you should start the media 
stream". But I think it is not a standard yet, and not too much vendors 
implemented the draft yet.

  Nils

On Tuesday 31 January 2006 03:16, Istvan De wrote:
> Hi!
>
> I've read about the above topic in the arcives and now I've got the same
> problem.
>
> User A is behind a symmetric NAT -> a new port is bound for every
> different
> (external ip, external port) pair.
> User B has a connection to the net without any NAT or firewall.
>
> User A wants to have a SIP+RTP session with user B. How?
>
> I guess basically what is needed is forming of a SIP
> message like "send the your reply to the same ip and
> same port from where you have received this" and user
> A can send this to user B.
>
> For the RTP session, a pretty similar thing would be
> needed like, A says to B: "I send you the RTP stream
> on your x port, send your rtp stream back to the same
> ip and port from where you receive mine".
>
> How to setup such a SIP packet?
> Or maybe there is a standard solution for this already?
> (STUN wont help in this case I guess, and TURN is not
> an option for me.)
>
> I've read about "symmetric SIP + symmetric RTP" maybe
> that is the same as I've described above?
>
> Thanks
> Istvan
>
>
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