Re: Preparing for discussion on what to do about the multipath extension milestone

Marten Seemann <martenseemann@gmail.com> Wed, 30 September 2020 09:30 UTC

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From: Marten Seemann <martenseemann@gmail.com>
Date: Wed, 30 Sep 2020 16:30:09 +0700
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Subject: Re: Preparing for discussion on what to do about the multipath extension milestone
To: Lucas Pardue <lucaspardue.24.7@gmail.com>
Cc: Olivier.Bonaventure@uclouvain.be, QUIC WG <quic@ietf.org>, Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>, Matt Joras <matt.joras@gmail.com>
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One of the pillars of standardization work at the IETF is running code.
Aside from some proof-of-concept implementations of multipath, I'm not
aware of any implementation supporting any kind of MPQUIC, let alone any
internet-wide experiments / deployments. From what I've seen on the interop
runner, a large number implementations are still struggling with connection
migration at the moment.

As others have said before, I do agree that multi-path is an intellectually
challenging problem. It's not a problem we're in a hurry to solve at the
current moment though: Given that QUIC is end-to-end encrypted, rolling out
MPQUIC should be a lot easier than rolling out MPTCP, as we won't have to
deal with ossified middleboxes.

Before devoting a significant amount of working group resources on this
particular problem, I'd like to see:

   1. one (or multiple) big players driving experimentation and
   internet-wide deployment and
   2. measurements that show that MPQUIC provides substantial benefits for
   real-world application protocols compared to vanilla QUIC with connection
   migration.


On Wed, Sep 30, 2020 at 4:14 PM Lucas Pardue <lucaspardue.24.7@gmail.com>
wrote:

>
> On Wed, 30 Sep 2020, 09:07 Olivier Bonaventure, <
> Olivier.Bonaventure@uclouvain.be> wrote:
>
>> Matt,
>> >      >
>> >      > On Fri, Sep 25, 2020 at 5:00 AM Lars Eggert <lars@eggert.org
>> >     <mailto:lars@eggert.org>
>> >      > <mailto:lars@eggert.org <mailto:lars@eggert.org>>> wrote:
>> >      >
>> >      >     In parallel to progressing the "base drafts" towards RFC
>> >      >     publications, the WG should now also begin to pick up the
>> pace on
>> >      >     our other adopted work items (ops drafts, extensions, etc.)
>> >      >
>> >      >     One important other discussion item is what to do about the
>> >      >     multipath extension milestone, which some have suggested
>> >     should be
>> >      >     dropped, while others still show interest to pursue it.
>> >      >
>> >      >
>> >      > So, I'd like to understand the suggestion to drop this milestone,
>> >     before
>> >      > I start trying to discuss that suggestion :-).
>> >
>> >     I'd like to understand this as well.
>> >
>> > I want to echo Jana's reply from the original discussion here
>> > <
>> https://mailarchive.ietf.org/arch/msg/quic/R-uJhzzXBz-93OTmYupXu8ooJdA/>.
>>
>> > Everyone agrees multi-path transports are an interesting problem, and
>> > IETF participants love to solve interesting problems. It's not clear,
>> > however, that it should be a primary milestone of the working group at
>> > this time.
>>
>> I think that the main question is whether the working group wants to
>> have a generic transport protocol which can support a variety of
>> applications or wants a transport that is only tuned to the requirements
>> of HTTP. Given QUIC's architecture and clean design, it is possible to
>> do a generic and future proof transport that includes clean multipath
>> support that is much better than MPTCP.
>>
>
> As an HTTP/3 implementer, I believe it to be the best example we have of a
> protocol that exercises the generic transport capabilities. Particularly
> stream multiplexing, HoL avoidance, synchronisation across independent
> streams, sensitivity to iwnd and cwnd, and large transfers in both
> directions.
>
> Yes, there are other application protocols. But I am not aware of ones
> that can so clearly demonstrate impacts of stream interactions. This can be
> in the form of user-perceived performance or industry metrics such as Web
> Vitals [1].
>
> HTTP is also a good example of a widely deployed application semantic that
> has been implemented across different libraries that have different design
> choices. This is an important consideration for the prioiritzation work
> because we need to consider what information an application is able to
> access from the transport, and how the application may/may not govern over
> transport behaviour. QUIC transport defines a set functions on streams that
> an application can rely upon [2], how does MP-QUIC augment that?
>
> I'm concerned about generic transport capabilities that cannot be
> reasonably used by applications without deep integration or layering
> violations. So it would be very useful for me to understand how a piece of
> HTTP server software (as an example of a real, complex application) would
> leverage MP-QUIC.
>
> [1] - https://web.dev/vitals/
> [2] - https://tools.ietf.org/html/draft-ietf-quic-transport-31#section-2.4
>