Re: [rtcweb] SAVPF history (Re: Final plea about SRTP)

Randell Jesup <randell-ietf@jesup.org> Tue, 08 May 2012 17:54 UTC

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Date: Tue, 08 May 2012 13:52:47 -0400
From: Randell Jesup <randell-ietf@jesup.org>
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Subject: Re: [rtcweb] SAVPF history (Re: Final plea about SRTP)
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On 5/8/2012 9:34 AM, Roman Shpount wrote:
>
> On Tue, May 8, 2012 at 3:57 AM, Harald Alvestrand <harald@alvestrand.no
> <mailto:harald@alvestrand.no>> wrote:
>
>     __
>     On 05/04/2012 07:45 PM, Roman Shpount wrote:
>>     I used to work on hardware endpoints that have been using SAVPF
>>     since 2004, with hundreds of thousands of units in the field.
>>
>>
>>     I thought SAVPF was only standardized in 2008 and AVPF was
>>     standardized in 2006. AVPF was discussed for a while though, so I
>>     would assumed you worked with something that implemented one of
>>     the drafts...
>     The -00 version of the SAVPF draft is dated 19 October 2003.
>
>     According to
>     https://datatracker.ietf.org/doc/draft-ietf-avt-profile-savpf/history/
>     publication was requested in February 2006, and it was approved by
>     the IESG in November 2007. The publication delay was 3 months.
>
>     The technical changes that resulted from these 4 years of work can
>     be seen here:
>
>     http://tools.ietf.org/rfcdiff?difftype=--hwdiff&url1=draft-ietf-avt-profile-savpf-00.txt&url2=draft-ietf-avt-profile-savpf-12.txt
>     <http://tools.ietf.org/rfcdiff?difftype=--hwdiff&url1=draft-ietf-avt-profile-savpf-00.txt&url2=draft-ietf-avt-profile-savpf-12.txt>
>
>
> I would say that something that changes to rfc4585 would be more
> relevant. Regardless of the actual changes in the draft, my point is
> there are very few actual SIP devices that implement SAVPF or AVPF.

Perhaps, though maybe it's more common in video (SIP INFO for IDR 
requests "sucks dead gerbils through garden hoses" - old Amiga slang 
phrase).

> Specifying this as the only profile supported by WebRTC will create yet
> another challenge to legacy interop, since it will require not only
> processing of ICE messages, and DTLS-SRTP re-encoding, but also RTCP
> re-generation.

AVPF has the advantage of being backward-compatible with AVP in almost 
all cases.  We used SAVPF internally, but typically hid that from the 
outside world by advertising AVP (this was long before SDP cap-neg was 
finalized).  (Has anyone truly implemented it?  In open source?)  IIRC 
this is even spoken to in the spec.  (We used AVP/AVPF instead of 
SAVP/SAVPF because we used the non-standardized "best effort encryption" 
draft I worked on with Hadriel, as an alternative/stopgap until cap-neg 
"worked".)

-- 
Randell Jesup
randell-ietf@jesup.org