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Re: [tcpm] adoption and implementation of draft-balasubramanian-tcpm-hystartplusplus-03

Yuchung Cheng <ycheng@google.com> Wed, 29 April 2020 19:10 UTC

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From: Yuchung Cheng <ycheng@google.com>
Date: Wed, 29 Apr 2020 12:09:41 -0700
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To: Martin Duke <martin.h.duke@gmail.com>
Cc: "tcpm@ietf.org Extensions" <tcpm@ietf.org>
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Subject: Re: [tcpm] adoption and implementation of draft-balasubramanian-tcpm-hystartplusplus-03
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+1 on adoption

two questions
1. RttSampleCount. Since the counter is incremented on a per ACK
basis, the receiver behavior may significantly influence the actual
hystart timeline. For example a receiver acking one full cwnd burst vs
acking every packet (or even every byte). it'd be good to clarify if
the intended rounds or time-scale in hystart++ design

2. "In practice, the Inter- Packet Arrival algorithm does not perform
well and is not able to detect congestion early, primarily due to ACK
compression." In my experience, another reason is it relies on packets
being pushed out in a window of burst in slow start. Therefore in
paced slow start (e.g. slow_start w/ linux fq/pacing) often produces
premature exit as well. I am curious if the authors have similar
experience?

Lastly, I am a fan of the BBR startup algorithm for obvious reasons.
The algorithm can be easily ported to produce an ssthresh for
conventional C.C.. It'd be great to see some words describing the
difference and even some real comparisons. BBR startup definitely
requires a lot more states (e.g. to track bw) for example. so there
are pros & cons.

On Wed, Apr 29, 2020 at 10:32 AM Martin Duke <martin.h.duke@gmail.com> wrote:
>
> I support adoption of this work.
>
> I would also encourage anyone in the WG thinking about implementing this draft to speak up. If this set is not null, I would encourage Praveen to move this draft to the Proposed Standard (preferred) or at least Experimental track.
>
> Martin
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