Re: [Sip] I-D Action:draft-ietf-sip-dtls-srtp-framework-00.txt

On Nov 13, 2007 11:50 AM, Francois Audet <audet@nortel.com> wrote:
> (copying Flemming)
>
> Good draft. Very helpful.
>
> On the SDP side of things.
>
> I didn't seen anything in the SDP format that specifically indicated in the offer that
> you are trying to setup DTLS-SRTP.
>
This is signaled in the SDP with the token "UDP/TLS/RTP/SAVP". See
http://www.ietf.org/internet-drafts/draft-fischl-mmusic-sdp-dtls-04.txt
for more details.


> Is the assumption that if there is no indication besides the RTP/SAVP in the tcap, that
> DTLS-SRTP may be negotiated, and that therefore we do not need an explicit indication
> that DTLS-SRTP is supported?
>
More specifically, UDP/TLS/RTP/SAVP. to signal we're sending SRTP over DTLS.

> Do we think it's good enough? In other words, is RTP/SAVP without a=crypto or a=key-mgmt
> good enough to indicate DTLS-SRTP? Or should we have another attribute?
>
I think this is good enough.

> A side comment is that the example shows usage with Best-Effort SRTP. My take is
> that it could also be used in "DTLS-SRTP-always" mode by having the m-line
> use UDP/TLS/RTP/AVP instead of RTP/AVP and not using a a=tcap/a=pcfg line. It
> would probably be worthwile to describe it in the draft.
>
I can add an example fragment to cover this case.


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