Re: [AVT] [Fwd: I-D ACTION:draft-zimmermann-avt-zrtp-02.txt]

Hi,

Generally I am agreeing with Colin here. Putting ZRTP handshake into 
RTCP is a clean solution. When it comes to broken boxes, like SBC I 
think it is fine to consider them but we shouldn't change everything 
simply to accommodate them. They are after all broken if they aren't 
supporting RTCP. Too broken boxes will need to be upgraded.

In regards to the bandwidth. Independent on if the handshake happens in 
RTP or RTCP there needs to be some checks on the bit-rate. We can't 
ignore congestion control when being deployed on a best effort network. 
Thus ZRTP should take care not to require completion within a specific 
time. Because the transfer of particular amount of data may take some 
time. So thinking that RTP will be better than RTCP in this regard may 
very well be an illusion. Also I think people are very looked into the 
5% BW rule instead of considering what RR and RS bandwidth modifier 
combined with AVPF actually can accomplish. For example RTCP can be 
configured to have low average BW and still allow substantially higher 
rates when needed.

Also I wonder how well ZRTP handles the mixer translator cases. I am 
sorry to say that I haven't read the latest ZRTP version. However I will 
try to do it before the meeting. Have the authors consider the example 
of topologies that can be existing as described in
http://tools.ietf.org/wg/avt/draft-ietf-avt-topologies/draft-ietf-avt-topologies-02.txt

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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