[Webtransport] Summary of today's interim and consensus call

[David Schinazi <[e-mail]>]

Hi WebTransport enthusiasts,

Thanks to everyone who joined today's virtual interim meeting. Our main
discussion point was flow control [1]. We discussed the following questions.

First, we discussed four options:
A) Do nothing
B) Add “hints” suggesting flow control breakdown
C) Add flow control to groups of QUIC streams
D) Add flow control to WebTransport over HTTP/3

Second, we discussed four potential approaches:
1) Adopt a flow control mechanism now; make it always mandatory.
2) Adopt a flow control mechanism now; make it mandatory for pooling
(browsers won’t pool if the mechanism is not supported).
3) Defer flow control; ship the current version of the draft, ship an
extension that would be prerequisite for pooling support in browsers later
(gives us more time).
4) Do nothing (existing QUIC flow control is sufficient).

We managed to reach consensus in the room that everyone could live with (D)
and (2). What this means in more detail:
* pooling means any time a WebTransport session shares resources with
anything else in the same HTTP connection (anything else could be a second
WebTransport session, or a regular GET request)
* pooling can only be used when flow control is supported by both endpoints
* flow control in WebTransport will use [2]
* clients can choose to not implement flow control, then they MUST NOT pool
* servers can choose to not implement flow control, then they MUST send
a WEBTRANSPORT_MAX_SESSIONS setting with value <= 1 to disable pooling

There is also more information available on the slides presented today [3]
and in the minutes [4]. The recording of the session will also be posted on
YouTube within a few days.

As chair, I'm formally starting a WG consensus call to confirm this
decision. If anyone objects to this outcome, please say so in reply to this
email. This consensus call will last for roughly two weeks and will end on
Friday March 8th, 2024 at 23:59 UTC.

Thanks,
David

[1] https://github.com/ietf-wg-webtrans/draft-ietf-webtrans-http3/issues/85
[2] https://datatracker.ietf.org/doc/draft-thomson-webtrans-session-limit/
[3]
https://datatracker.ietf.org/meeting/interim-2024-webtrans-02/materials/slides-interim-2024-webtrans-02-sessa-webtrans-wg-virtual-interim-slides-04.pdf
[4]
https://datatracker.ietf.org/doc/minutes-interim-2024-webtrans-02-202402222100/