[R-C] New Version Notification for draft-alvestrand-rmcat-remb-00.txt

[Colin Perkins]

On 19 Jan 2012, at 07:45, Harald Alvestrand wrote:
> On 01/18/2012 11:37 PM, Colin Perkins wrote:
>> 
>> Harald,
>> 
>> A couple of suggestions:
>> 
>> - This uses RTCP Payload-specific feedback messages, with the Application Layer feedback (AFB) FMT parameter and a 4 octet unique identifier (REMB) inside the feedback section. The AFB message was intended to be private for a particular application, and not something that should be standard. This would be better registered as a new FMT value within the payload-specific feedback messages. Doing so would also save 4 octets, since you wouldn't need to unique identifier field.
> Agreed; we published this for experimentation, in order to get some experience with it without breaking any standards; its usage is "private" in the sense of being limited to the people participating in the experiment.
> 
> I think the draft said so, but I may not have been clear enough; will try to improve.
> Once we have rough consensus that this approach makes sense, I think we should give the "real" format as a new FMT value, and document this format in an appendix as "for experimentation in advance of FMT assignment". Let's hope we can get it done soon.
> 
> Advice sought for IANA considerations:
> 
> Offhand, I can't find the registry for FMT values; RFC 4585 section 6.3 seems to specify 5 values (out of 32 possible codes), with RFC 5104 section 4.3 assigning 4 more. It's a small field, so I really don't want to waste codepoints.
> 
> Section 9 of RFC 4585 says that the rule for new entries is "specification required" according to RFC 2434, which is "an RFC or other permanent and readily available reference", which would preclude I-D.
> 
> There's also (to my mind) an open question on whether this should be a Payload Specific message (206) or a Transport Layer Feedback Message (205). Any reason not to go with a Transport Layer feedback message?

I did think about suggesting a transport layer feedback message too, so yes that may make sense.


>> - You have an SSRC feedback field but don't use the SSRC of media source. Would it make sense to use the SSRC of media source to hold the first entry of the SSRC feedback field, and put the others in the payload? Again, saves 4 octets, and avoids a wasted field.
> If there's no equipment that tries to "generically" parse these messages, we can certainly do so! Since RFC 5104 section 4.2.2.2 seemed to not take the opportunity to skip this field, we thought we'd follow precedent until we felt safe.

The semantics look to be "this estimated maximum rate applies to this list of media sources", which seems to fit the "SSRC of media source" field, unless I misunderstood something.

-- 
Colin Perkins
http://csperkins.org/



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