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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