Subject: Re: [rmcat] I-D Action: draft-ietf-rmcat-nada-05.txt

From: "Bless, Roland (TM)" <[email-masked]>
Date: Fri, 27 Oct 2017 17:04:35 +0200

Hi,

I just read draft-ietf-rmcat-nada-05.txt for the first time and have
some (probably dumb) questions (mainly related to the delay-based part):
- The draft mentions a "15-tap minimum filter" (p. 12) and a
  "15-tab minimum filter" (p. 16). One of the seems to contain
  a type. Moreover, I have no clue what that actually is.
  Is it simply a minimum filter over the last 15 measured
  values?

- The description in 4.2 states:
      update baseline delay: d_base = min(d_base, d_fwd)
  is this where the minimum filter is applied? If so
  better use min_filtered(d_base, d_fwd) and define
  what that is.

- 4.3 mentions "base delay expiration", but I wasn't able
  to find a discussion in section 5 about it.

- 5.1.1: "All delay estimations are based on sender timestamps with
  higher granularity than RTP timestamps."

  I'm not sure. RTP timestamps depend on the sampling clock frequency
  and this can be quite high, e.g., 8kHz corresponds to 125µs, 90kHz
  to 11µs. System clock resolution can be in the range of microseconds
  and sometimes even nanoseconds. So more interesting would be to state
  what minimum resolution the sender timestamps should have.

- 6.3 "that a feedback interval below 250ms will not break
  up the feedback control loop of NADA congestion control."

  This is not clear to me. Does a "feedback interval below 250ms"
  mean a smaller interval and thus more frequent feedback?
  "feedback below 250 ms" could also mean slower and less frequent
  feedback.
  If so, I don't understand why more frequent feedback would
  "break up the feedback control loop". An unambiguous
  statement would be better.

Regards,
 Roland