Re: Multi-path QUIC Extension Experiments

[Robin MARX <[e-mail]>]

Hello Yanmei,

Thanks for the additional results on an interesting topic. I'm looking
forward to reading the SIGCOMM paper.

I was a bit surprised to (apparently) see HOL blocking mentioned as a major
issue, as that's one of the things QUIC aims to be better at than TCP.
It's a bit difficult to understand from the slides, but it seems like
you're sending packets for a single stream (Stream ID 1 in the diagrams) on
both the slow and fast path, which would indeed induce HOL blocking.
Consequently, I was wondering what the practical reasons are for you to
multiplex packets for a single stream over multiple paths, as opposed to
for example attaching a single stream to a single path (say: high priority
streams use the fast path for all their packets).

I see this mentioned a bit in the draft under "packet scheduling", where it
talks about switching paths once the cwnd is full for one. That indeed
leads to the behaviour seen in the slides, but that's my question: why
would you take those approaches then?
Are there so many cases where the additional "bandwidth" from using
multiple path's cwnd for a single stream outweigh the downsides of HOL
blocking? Relatedly: what are the packet loss rates you've observed on
real networks?
Have you experimented with e.g., tying streams to paths more closely? Does
that work better or worse? Why?

I'm mainly wondering how these tradeoffs evolve depending on the type of
paths available and if it's possible to make a model to drive this logic.
I assume there is much existing work on this for MPTCP, but I also assume
some of that changes due to QUIC's independent streams / stream
prioritization flexibility.

Thank you in advance and with best regards,
Robin


On Sun, 11 Jul 2021 at 20:48, Yanmei Liu <miaoji.lym=
[e-mail]> wrote:

> Hi everyone,
>
> We have finished some experiments about deploying multi-path quic
> extension(https://datatracker.ietf.org/doc/draft-liu-multipath-quic/) in
> Alibaba Taobao short-form video streaming, and the experiment results are
> concluded in the slides (attached file).
> If anyone is interested in the experimental details about multi-path quic,
> please let us know.
> All the feedbacks and suggestions are appreciated!
>
> Best regards,
> Yanmei
>


-- 

dr. Robin Marx
Postdoc researcher - Web protocols
Expertise centre for Digital Media

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