Re: francois' comments and why RFC4474 not used in the field

On Mar 31, 2009, at 8:24 PM, Cullen Jennings wrote:

>
> In all of section 8, the only reason I find of why things are  
> changed is
>
> "For media steering purposes, B2BUAs in intermediate domains need to  
> modify the IP address c-lines and the port in m-lines."
> Even this one line leaves me confused about what intermediate  
> domains are in the deployment cases where this happens and if we are  
> talking about email style address or e.164 style addresses. What an  
> example is of a deployment where things like this happen and why the  
> middle (not the end domains) do the media steering. When I ask this  
> of example people give me, if often turns out what is really wanted  
> is not media steering but the middle to be able to hide the fact  
> that they actually delivered the call to a third provider for PSTN  
> termination.
>

I'll agree that topology hiding is a use case for port/address  
obfuscation that results in RFC 4474 not working, thereby preventing  
DTLS/SRTP key fingerprinting when topology-hiding occurs.

Design alternatives include tunnels and STUN relays combined with  
header obfuscation  and UA support for selective obfuscation for the  
offer. While these sorts of triggerworks might work, they're a lot  
more complex than just editing the SDP.

--
Dean

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