[Bloat] dash traffic "chunklets" verses pie and fq_codel

[Dave Taht]

Jonathan Morton <chromatix99 at gmail.com> writes:

> While interesting from a scientific point of view, I do think they're trying to
> solve the wrong problem here.

I am always interested in someone repeating an experiment with a few
more variables altered. In this case, pacing and BBR would be rather
interesting to see.

>
> As stated in the paper, the big problem with DASH is the tendency of TCPs to
> revert to slow start (ie. beginning from a small cwnd) after a gap in
> availability of data to transmit. If that occurs after as short an interval as 2
> seconds (the DASH chunk length), I consider that to be a flaw in those TCP
> implementations.

We also have the decay factors present in the available AQMs.

> Theoretically, 2 seconds is as long as DASH should wait while playing video
> continuously, in the steady state condition where the link capacity is known and
> the buffer is full. I can see little reason for it to wait longer; I would
> consider that an implementation flaw in the DASH client.
>
> Also, given a nearly full buffer, I would expect DASH to resist reducing the
> video quality due to a possibly transient reduction in measured link capacity.
> If the reduction persists long enough to substantially empty the buffer (say to
> 50%), then it would be reasonable to step down in quality to match the new
> measurement. Again, this is a quality of implementation problem in the client.
>
> The other problem their solution addresses, but is not stated as the primary
> goal, is to reduce DASH susceptibility to competition versus multiple flow
> applications such as Steam downloads. But that is not a problem specific to flow
> isolating AQM systems (if anything, it's worse with plain FIFO). They do note
> that fq_codel greatly improves the situation versus reverse bulk traffic, just
> as it should, but they don't seem to highlight that this benefit is reduced with
> "chunklets" in use, according to the measurements presented.

My overall joy is generally that "things are better" with fq_codel based queuing
solutions than anything else we've yet devised, for yet another form of
traffic.

Really the only thing left that I worry about (technically) is
videoconferencing. It's crossing the chasm to the places where these
technologies are most needed - where we have devices with first
world fifo over-buffering being deployed into third world bandwidths,
and still no headends for any last mile tech (dsl, cable, etc) actually
implementing stuff like this. There's a lot of the world left to cover
with better Internet.

https://trends.google.com/trends/explore?q=bufferbloat

>
> - Jonathan Morton
>
>
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