Subject: [tsvwg] I-D Action: draft-ietf-tsvwg-l4sops-01.txt

From: [email-masked]
Date: Mon, 12 Jul 2021 16:01:43 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Transport Area Working Group WG of the IETF.

        Title           : Operational Guidance for Deployment of L4S in the Internet
        Author          : Greg White
	Filename        : draft-ietf-tsvwg-l4sops-01.txt
	Pages           : 21
	Date            : 2021-07-12

Abstract:
   This document is intended to provide guidance in order to ensure
   successful deployment of Low Latency Low Loss Scalable throughput
   (L4S) in the Internet.  Other L4S documents provide guidance for
   running an L4S experiment, but this document is focused solely on
   potential interactions between L4S flows and flows using the original
   ('Classic') ECN over a Classic ECN bottleneck link.  The document
   discusses the potential outcomes of these interactions, describes
   mechanisms to detect the presence of Classic ECN bottlenecks, and
   identifies opportunities to prevent and/or detect and resolve
   fairness problems in such networks.  This guidance is aimed at
   operators of end-systems, operators of networks, and researchers.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-l4sops/

There is also an HTML version available at:
https://www.ietf.org/archive/id/draft-ietf-tsvwg-l4sops-01.html

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-tsvwg-l4sops-01

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

---

From: Pete Heist <[email-masked]>
Date: Tue, 13 Jul 2021 12:16:47 +0200

Hi Greg,

Regarding the guidance for general purpose servers in Section 4:

---
*  Taking action based on the detection of RFC3168 FIFO
   bottlenecks is likely not needed for short transactional
   transfers (e.g. sub 10 seconds) since these are unlikely to
   achieve the steady-state conditions where unfairness has been
   observed.
---

Do you have any data to back up the sub 10 seconds threshold?

What we've seen is non-L4S flows yielding quickly to L4S flows in
RFC3168 queues. In this plot of Prague vs CUBIC in a single Codel
queue, the flows start at T=5 seconds, harm to CUBIC occurs almost
immediately, and CUBIC's steady state near minimum cwnd is reached 4-5
seconds after flow start:

https://sce.dnsmgr.net/results/l4s-2020-11-11T120000-final/l4s-s6-rfc3168-1q/l4s-s6-rfc3168-1q-ns-prague-vs-cubic-noecn-fq_codel-50Mbit-20ms_tcp_delivery_with_rtt.svg

We also posted a test showing the FCT harm to short flows by a single
long flow, where flow lengths for the short flows were taken from a
lognormal distribution with a P5 of 64KB and a P95 of 2MB:

https://github.com/heistp/ccafct#sample-output

Thanks,
Pete

---

From: Pete Heist <[email-masked]>
Date: Thu, 29 Jul 2021 11:19:15 +0200

Regarding the sub 10 seconds guidance topic that came up in Monday's
meeting, there wasn't much response when the question was raised what
the guidance should be, probably because it's complicated, and depends
upon, at a minimum, RTT, flow lengths, the exact CCAs and AQM in use,
what metric matters to the application, etc. As we have shown in our
FCT data linked to earlier in this thread, the harm in 3168 queues
isn't limited to rate unfairness.

In the interest of keeping things simple, what about just removing that
bullet?

Otherwise, we might want to perform more extensive FCT tests with a
range of flow lengths, RTTs, bandwidths and CCAs, and I'm not sure if
anyone has the time to test this at the moment.

Pete

On Tue, 2021-07-13 at 12:16 +0200, Pete Heist wrote:
> > This draft is a work item of the Transport Area Working Group WG of
> > the
> > IETF.
> > 
> >         Title           : Operational Guidance for Deployment of
> > L4S in
> > the Internet
> >         Author          : Greg White