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

See below. 

> -----Original Message-----
> From: jason.fischl@gmail.com [mailto:jason.fischl@gmail.com] 
> On Behalf Of Jason Fischl
> Sent: Monday, December 03, 2007 16:07
> To: Audet, Francois (SC100:3055)
> Cc: sip@ietf.org; Hannes.Tschofenig@nsn.com; 
> ekr@networkresonance.com; Flemming Andreasen
> Subject: 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-dt
> ls-04.txt
> for more details.

Ah.... Can you explicitly say that in the document?
I see there is a reference to this draft, but the document doesn't say 
that it is used for that purpose.

> 
> > 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.

Agreed.

> > 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.

That would be very useful.

Thanks.

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