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Re: [AVT] Comments on draft-ietf-avt-tfrc-profile-05

On 6 Nov 2005, at 21:36, Magnus Westerlund wrote: 
I have reviewed the draft and have some comments:

1. Section 2. A benefit for DCCP is also its possibilities to negotiate future defined congestion control mechanisms.

2. Section 4. RTP data header extension: I think both of the SHOULDs in this paragraph needs to be MUST. Yes, I am arguing that AVP has to relaxed wording in regards to header extensions.

3. Section 4. RTP data header extension: Is the first 16 bits field values shared with the AVP profile or is this a new scope?

4. Section 4. RTCP report interval: "This profile is restricted to unicast flows, therefore at all times there is only one active sender and one receiver." This formulation is a bit unclear. As there may only be unicast traffic but that doesn't present there from being multiple sources (SSRC).

5. Section 4. Encapsulation: Should this profile be defined for use over UDP-Lite?

I'm not sure we have a good understanding of how TFRC should respond to corruption based loss?

6. Section 5.2, first bullet: I would like to add the word "transmission" before timestamp to clarify what timestamp is indicated here as the packet will contain multiple ones.

7. Section 7. Also for (t_i) should it be indicated that it is the transmission timestamp that is referred to.

8. This draft is still not declaring the possibility to use AVPF RTCP feedback messages.

9. Something that maybe should be clarified is if any congestion control actually occur of the return path. What will feedback message packet losses mean for the forward link and will that induce any reduction in the feedback traffic. In TCP losses of ACK will implicitly mean a reduction of the forward traffic which in its turn reduces the ACK path. However it is not obvious that TFRC will result in this. Which makes me question if some criteria for the handling of the feedback path is needed. 

We should probably just follow RFC 3448 here; clarifying that if needed.

Cheers,
Colin


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