Subject: [tsvwg] tests of L4S harm to video streaming services in RFC3168 queues

From: Pete Heist <[email-masked]>
Date: Fri, 06 Aug 2021 20:12:01 +0200

During the last IETF meeting we did a few "real-world" tests of L4S.
This first of these tests looked at how video streaming services
perform in single RFC3168 Codel queues, when in competition first with
TCP CUBIC, then with TCP Prague:

https://github.com/heistp/l4s-tests/#harm-to-video-streaming-services

The results suggest a couple of things:

1) that harm in single RFC3168 queues goes beyond just harm to long-
running flows. This is something we already showed theoretically
(https://github.com/heistp/l4s-tests/#harm-to-short-tcp-flows), but
video streaming tests may be a little more tangible.

2) that QUIC/BBR (if BBR is what's in use here) seems to be harmed less
than conventional TCP is by Prague. While the YouTube video we tested
saw a bitrate/resolution reduction with Prague, it did not freeze,
whereas both services that appear use conventional TCP did.

We'll use some of these results in a later analysis, but if there's any
further commentary on them, it might be useful.

Pete