[OpenSIPS-Users] Mediaproxy ICE negotiations

[John Quick]

Many thanks. I had not seen the slideshare.net information before. It is
very good.

I have another question on the same subject.  In a call like this:
UAC (supports ICE) -- INVITE -->  OpenSIPS/Mediaproxy  -- --> UAS (does not
support ICE)

..if OpenSIPS calls engage_mediaproxy() for every call, then Mediaproxy will
be used because the SDP "c=" parameter will have been modified.
For a similar call where the UAS *does* support ICE, then "c=" will be
ignored in favour of using ICE negotiation. Is that right?

John Quick


-----Original Message-----
From: Saúl Ibarra Corretgé [mailto:saul at ag-projects.com] 
Sent: 02 March 2012 10:37
To: john.quick at smartvox.co.uk; OpenSIPS users mailling list
Subject: Re: [OpenSIPS-Users] Mediaproxy ICE negotiations

Hi,

On Mar 2, 2012, at 10:41 AM, John Quick wrote:

> Using Blink and other ICE compatible clients with Mediaproxy 2.x and 
> OpenSIPS 1.7.x, I have been looking at some packet captures and 
> reading RFC 5245. I would like to get a deeper understanding of how 
> ICE works and the roles OpenSIPS and Mediaproxy play.
> 
> With Mediaproxy as a low priority "ice_candidate" (set using modparam) 
> I can see that OpenSIPS adds the address of the Mediaproxy to the list 
> of ICE candidates in the SDP. It sets the type to 'relay'. Devices 
> that support ICE are required to sort and select potential candidates 
> then test connectivity
> - one of the connectivity tests uses STUN requests. In my packet 
> captures, I could see the UAC sending STUN requests to candidates of 
> type "host", but did not see any sent to the Mediaproxy (this might 
> have been because the other candidates were higher priority). I 
> wondered how Mediaproxy is able to handle the STUN requests used 
> during connectivity tests. Does it respond to them directly or is it 
> somehow able to relay the requests in the same way as it would relay 
> the RTP? Or should it never receive them because it is a relay?
> 

MediaPRoxy will relay STUN packets in userland until it receives one RTP
packet from each endpoint. If the MediaProxy candidate was not chosen (no
STUN binding request with flag set was received) it will do nothing, just
bail out. If MediaPRoxy candidate was chose, a conntrack rule will be added
and relaying will begin in kernel.

> Is there any documentation I may have missed that explains this?
> 

Have a look at these:

http://mediaproxy-ng.org/wiki/ICE
http://www.slideshare.net/saghul/ice-4414037


Regards,

--
Saúl Ibarra Corretgé
AG Projects