[AVTCORE] AD review of draft-ietf-avtcore-cc-feedback-message-07

Barry Leiba <barryleiba@computer.org> Thu, 23 July 2020 21:38 UTC

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From: Barry Leiba <barryleiba@computer.org>
Date: Thu, 23 Jul 2020 17:38:28 -0400
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Subject: [AVTCORE] AD review of draft-ietf-avtcore-cc-feedback-message-07
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Thanks for the work on this clear, easy-to-read document, and I'm
sorry it took me a while to get through the workload to review it.
Here's my AD review, and I'll set the state to "revised I-D needed"
and start last call after -08 is posted.

Everything here is minor; please let me know if you disagree with
anything below.

— Section 1 —
Please include reference citations for RTP and RTCP.

   As a direct result,
   the different congestion control (i.e., rate adaptation) designs are
   not interoperable.

Is “i.e.,” the right term here, or do you mean “such as”?  I would
also move the parenthetical one word later, rather than having it
split the phrase “congestion control designs”.

— Section 2 —
Please use the current BCP 10 boilerplate, found in RFC 8174, and add
a normative reference to that RFC.

— Section 3 —

   o  RTP sequence number: The receiver of an RTP flow needs to feedback
      the sequence numbers of the received RTP packets to the sender

Nit: “feed back”, as a verb, should be two words.  Or perhaps “needs
to feed the sequence numbers … back to the sender”.  (Check other uses
of “feedback” as a verb also.)

— Section 3.1 —

   The contents of each 16-bit packet metric block comprises the L, ECN,
   and ATO fields are as follows:

Nit: It looks like “are” is an extra word here, yes?

      1 represent the
      packet was received and the subsequent bits in the block need to
      be parsed.

Nit: “1 represents that the”

— Section 5 —

   However, if
   multiple consecutive congestion control feedback packets are lost,
   the sender SHOULD rapidly reduce its sending rate towards zero, as
   this likely indicates a path failure.

Doesn’t “reduce” already mean “towards zero”?  Is something further
meant by saying “towards zero” that should be made clearer (I suspect

— Section 6 —

   When used with "ccfb" feedback, the wildcard payload type ("*") MUST
   be used.

This doesn’t read well as written, and sorta doesn’t make much sense.
I think you just want to say this:

   The payload type used with “ccfb” feedback MUST be the wildcard type (“*”).

— Section 8 —

   An efficient congestion control algorithm requires more fine grained
   information on per packet reception quality

Nit: hyphenate “fine-grained” and “per-packet”.  Also hyphenate the
former in the following sentence.

      This is the opposite of the sender based congestion
      control approach suggested in this memo, so TMMBR cannot be used
      to convey the information needed for a sender based congestion

Nit: hyphenate “sender-based” in both places, and also at the end of
the section.

— Section 11 —

   at a greater rate than the path can support, thereby congesting the

Is “congesting” really used as a verb generally?  Better as “thereby
causing congestion on the path.”