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David,<br>
<br>
<div class="moz-cite-prefix">On 17/03/2019 18:07, David P. Reed
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1552846034.909628287@apps.rackspace.com">
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<font size="3" face="arial">
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">Vint -</p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">BBR is the end-to-end
control logic that adjusts the source rate to match the share
of the bolttleneck link it should use.</p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">It depends on getting
reliable current congestion information via packet drops
and/or ECN.</p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">So the proposal by these
guys (not the cable guys) is an attempt to improve the quality
of the congestion signal inserted by the router with the
bottleneck outbound link.</p>
</font></blockquote>
<font size="3"><font face="arial">What do you mean 'not the cable
guys'?<br>
This thread was reasonably civil until this intervention.<br>
<br>
</font></font>
<blockquote type="cite"
cite="mid:1552846034.909628287@apps.rackspace.com"><font size="3"
face="arial">
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">THe cable guys are trying to
get a "private" field in the IP header for their own use.</p>
</font></blockquote>
<br>
There is nothing private about this codepoint, and there never has
been. Here's some data points:<br>
<br>
* The IP header codepoint in question (ECT(1) in the ECN field) was
proposed for use as an alternative ECN behaviour in July 2105 in the
IETF AQM WG and the IETF's transport area WG (which handles all ECN
matters). <br>
* A year later there followed a packed IETF BoF on the subject
(after 2 open Bar BoFs). <br>
* Long discussion ensued on the merits of different IP header field
combinations, on both these IETF lists, involving people active on
this list (bloat), including Dave Taht, who is acknowledged for his
contributions in the IETF draft. <br>
* That was when it was decided that ECT(1) was most appropriate. <br>
* The logic of the decision is written up in an appendix of
draft-ietf-ecn-l4s-id. <br>
* David Black, one of the co-chairs of the IETF's transport area WG
and co-author of both the original ECN and Diffserv RFCs, wrote
RFC8311 to lay out the process for reclaiming and reusing the
necessary codepoints. <br>
* This work and the process of freeing up codepoints has been very
visible at every IETF ever since, with multiple drafts to fix other
aspects of the protocols working their way through the IETF process
in multiple WGs (tsvwg, tcpm, trill, etc). <br>
* L4S has also been mentioned in IETF liaisons with the IEEE and
3GPP.<br>
<br>
Some history:<br>
* I had been researching the idea since 2012. <br>
* In fact my first presentation on it was scheduled directly after
Van Jacobson's first presentation of CoDel at the IETF in July 2012.
VJ overran by nearly 20mins leaving just 3 mins for my presentation.<br>
* Mirja Kuehlewind and I did early groundwork in 2013 and published
a paper<br>
* Then I (working for BT) brought the work into the EU RITE project
(Reducing Internet Transport Latency) with Simula, Alcatel-Lucent,
etc. <br>
* By 2015 the two main L4S proponents were Koen De Schepper from
Alcatel Lucent and myself (I had just switched from BT to Simula),
along with Olga Bondarenko (now Albisser), a PhD student at Simula
who now works for Microsoft (on something else) and is still doing
her PhD part-time with Simula<br>
o By that time, Al-Lu and Simula had a cool prototype running. <br>
o This was demonstrated publicly for the first time in the IETF
AQM WG over DC+core+backhaul+DSL+home networks. <br>
<a class="moz-txt-link-freetext" href="https://riteproject.eu/dctth/#1511dispatchwg">https://riteproject.eu/dctth/#1511dispatchwg</a><br>
* In May 2016, L4S was demonstrated at MultiMediaSystems'16 with
/every/ packet from all the following simultaneous applications
achieving ~1ms queuing delay or less over a 40Mb/s Internet access
link (7ms base RTT):<br>
o cloud-rendered remote presence in a racing car within a VR
headset<br>
o the interactive cloud-rendered video already linked above<br>
o an online gaming benchmark<br>
o HAS video streaming<br>
o a number of bulk file downloads<br>
o a heavy synthetic load of web browsing<br>
<br>
L4S has never been access-technology-specific. Indeed the cable
industry has been funding my work at the IETF to help encourage a
wider L4S ecosystem. There is nothing private to the cable industry
in this:<br>
* Al-Lu used DSL as a use-case, but L4S was relevant to all the
access technologies they supplied. <br>
* BT was obviously interested in DSL, <br>
* but BT's initial motivating use-case was to incrementally deploy
the low queuing delay of DCTCP over BT's data centre interconnect
networks. <br>
* In Jul 2016 the open-source Linux repo for the Coupled AQM was
published, with a fully working version to be used and abused. <br>
Now at: <a class="moz-txt-link-freetext" href="https://github.com/L4STeam/sch_dualpi2_upstream">https://github.com/L4STeam/sch_dualpi2_upstream</a><br>
* Of course, DCTCP was already open-sourced in Linux and FreeBSD, as
well as available in Windows<br>
* In Jul 2016, the main IETF BoF on L4S was held:<br>
o Ingemar Johansson from Ericsson was one of the proponents,
focused on using L4S in LTE<br>
o along with Kevin Smith from Vodafone and <br>
o Praveen Balasubramanian from Microsoft (who maintains the
Windows TCP stack, including DCTCP).<br>
o Ingemar has since written an open-source L4S variant of the
SCReAM congestion controller for real-time media:
<a class="moz-txt-link-freetext" href="https://github.com/EricssonResearch/scream/">https://github.com/EricssonResearch/scream/</a><br>
o Mirja Kuehlewind of ETHZ (and now Ericsson) implemented the
necessary feedback in TCP <a class="moz-txt-link-freetext" href="https://github.com/mirjak/linux-accecn">https://github.com/mirjak/linux-accecn</a><br>
* In summer 2017 CableLabs started work on Low Latency DOCSIS, and
hired me later in the year to help develop and specify it, along
with support for L4S<br>
o In Jan 2019 the Low Latency DOCSIS spec was published and is now
being implemented.<br>
o You can find the primary companies involved at the end of the
White Paper.
<a class="moz-txt-link-freetext" href="https://cablela.bs/low-latency-docsis-technology-overview-february-2019">https://cablela.bs/low-latency-docsis-technology-overview-february-2019</a><br>
o Operators:<br>
Liberty Global<br>
Charter<br>
Rogers<br>
Comcast<br>
Shaw<br>
Cox Communications<br>
o Equipment vendors<br>
ARRIS<br>
Huawei<br>
Broadcom<br>
Intel<br>
Casa<br>
Nokia<br>
Cisco<br>
Videotron<br>
* Nicolas Kuhn of CNES has been assessing the use of L4S for
satellite.<br>
* Magnus Westerlund of Ericsson with a team of others has written
the necessary ECN feedback into QUIC<br>
* L4S hardware is also being implemented for hi-speed switches at
the moment <br>
(the developer wants to announce it themselves, so I have been
asked not to identify them). <br>
<br>
There's a lot more stuff been going on, but I've tried to pick out
highlights.<br>
<br>
All this is good healthy development of much lower latency for
Internet technology.<br>
<br>
<br>
I find it extremely disappointing that some people on this list are
taking such a negative attitude to the major development in their
own field that they seem not to have noticed since it first hit the
limelight in 2015. <br>
<br>
L4S has been open-sourced since 2016 so that everyone can develop it
and make it better...<br>
<br>
If I was in this position, having overlooked something important for
multiple years, I would certainly not condemn it while I was trying
to understand what it was and how it worked. Can I suggest everyone
takes a step back, and suspends judgement until they have understood
the potential, the goals and the depth of what they have missed.
People who know me, know that I am very careful with Internet
architecture, and particularly with balancing public policy against
commercial issues. Please presume respect unless proven otherwise.<br>
<br>
Best Regards<br>
<br>
<br>
<br>
Bob<br>
<br>
PS. Oh and BBR would be welcome to use the ECT(1) codepoint to get
into the L4S queue. But only if it can keep latency down below
around 1ms. Currently those ~15-25ms delay spikes would not pass
muster. Indeed, its delay is not consistently low enough between the
spikes either.<br>
<br>
<br>
<br>
<blockquote type="cite"
cite="mid:1552846034.909628287@apps.rackspace.com"><font size="3"
face="arial">
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;"> </p>
<p style="margin:0;padding:0;font-family: arial; font-size:
12pt; overflow-wrap: break-word;">-----Original Message-----<br>
From: "Vint Cerf" <a class="moz-txt-link-rfc2396E" href="mailto:vint@google.com"><vint@google.com></a><br>
Sent: Saturday, March 16, 2019 5:57pm<br>
To: "Holland, Jake" <a class="moz-txt-link-rfc2396E" href="mailto:jholland@akamai.com"><jholland@akamai.com></a><br>
Cc: "Mikael Abrahamsson" <a class="moz-txt-link-rfc2396E" href="mailto:swmike@swm.pp.se"><swmike@swm.pp.se></a>, "David P.
Reed" <a class="moz-txt-link-rfc2396E" href="mailto:dpreed@deepplum.com"><dpreed@deepplum.com></a>,
<a class="moz-txt-link-rfc2396E" href="mailto:ecn-sane@lists.bufferbloat.net">"ecn-sane@lists.bufferbloat.net"</a>
<a class="moz-txt-link-rfc2396E" href="mailto:ecn-sane@lists.bufferbloat.net"><ecn-sane@lists.bufferbloat.net></a>, "bloat"
<a class="moz-txt-link-rfc2396E" href="mailto:bloat@lists.bufferbloat.net"><bloat@lists.bufferbloat.net></a><br>
Subject: Re: [Ecn-sane] [Bloat] [iccrg] Fwd: [tcpPrague]
Implementation and experimentation of TCP Prague/L4S hackaton
at IETF104<br>
<br>
</p>
<div id="SafeStyles1552845686">
<div dir="ltr">where does BBR fit into all this?
<div>v</div>
</div>
<br>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Sat, Mar 16, 2019 at
5:39 PM Holland, Jake <<a
href="mailto:jholland@akamai.com" moz-do-not-send="true">jholland@akamai.com</a>>
wrote:</div>
<blockquote class="gmail_quote" style="margin: 0px 0px 0px
0.8ex; border-left: 1px solid #cccccc; padding-left: 1ex;">On
2019-03-15, 11:37, "Mikael Abrahamsson" <<a
href="mailto:swmike@swm.pp.se" target="_blank"
moz-do-not-send="true">swmike@swm.pp.se</a>> wrote:<br>
L4S has a much better possibility of actually getting
deployment into the <br>
wider Internet packet-moving equipment than anything
being talked about <br>
here. Same with PIE as opposed to FQ_CODEL. I know
it's might not be as <br>
good, but it fits better into actual silicon and it's
being proposed by <br>
people who actually have better channels into the
people setting hard <br>
requirements.<br>
<br>
I suggest you consider joining them instead of
opposing them.<br>
<br>
<br>
Hi Mikael,<br>
<br>
I agree it makes sense that fq_anything has issues when
you're talking<br>
about the OLT/CMTS/BNG/etc., and I believe it when you
tell me PIE<br>
makes better sense there.<br>
<br>
But fq_x makes great sense and provides real value for the
uplink in a<br>
home, small office, coffee shop, etc. (if you run the
final rate limit<br>
on the home side of the access link.) I'm thinking maybe
there's a<br>
disconnect here driven by the different use cases for
where AQMs can go.<br>
<br>
The thing is, each of these is the most likely congestion
point at<br>
different times, and it's worthwhile for each of them to
be able to<br>
AQM (and mark packets) under congestion.<br>
<br>
One of the several things that bothers me with L4S is that
I've seen<br>
precious little concern over interfering with the ability
for another<br>
different AQM in-path to mark packets, and because it
changes the<br>
semantics of CE, you can't have both working at the same
time unless<br>
they both do L4S.<br>
<br>
SCE needs a lot of details filled in, but it's so much
cleaner that it<br>
seems to me there's reasonably obvious answers to all (or
almost all) of<br>
those detail questions, and because the semantics are so
much cleaner,<br>
it's much easier to tell it's non-harmful.<br>
<br>
<aside regarding="non-harmful"><br>
The point you raised in another thread about reordering is
mostly<br>
well-taken, and a good counterpoint to the claim
"non-harmful relative<br>
to L4S".<br>
<br>
To me it seems sad and dumb that switches ended up trying
to make<br>
ordering guarantees at cost of switching performance,
because if it's<br>
useful to put ordering in the switch, then it must be
equally useful to<br>
put it in the receiver's NIC or OS.<br>
<br>
So why isn't it in all the receivers' NIC or OS (where it
would render<br>
the switch's ordering efforts moot) instead of in all the
switches?<br>
<br>
I'm guessing the answer is a competition trap for the
switch vendors,<br>
plus "with ordering goes faster than without, when you
benchmark the<br>
switch with typical load and current (non-RACK)
receivers".<br>
<br>
If that's the case, it seems like the drive for a
competitive advantage<br>
caused deployment of a packet ordering workaround in the
wrong network<br>
location(s), out of a pure misalignment of incentives.<br>
<br>
RACK rates to fix that in the end, but a lot of damage is
already done,<br>
and the L4S approach gives switches a flag that can double
as proof that<br>
RACK is there on the receiver, so they can stop trying to
order those<br>
packets.<br>
<br>
So point granted, I understand and agree there's a cost to
abandoning<br>
that advantage.<br>
</aside><br>
<br>
But as you also said so well in another thread, this is
important. ("The<br>
last unicorn", IIRC.) How much does it matter if there's
a feature that<br>
has value today, but only until RACK is widely deployed?
If you were<br>
convinced RACK would roll out everywhere within 3 years
and SCE would<br>
produce better results than L4S over the following 15
years, would that<br>
change your mind?<br>
<br>
It would for me, and that's why I'd like to see SCE
explored before<br>
making a call. I think at its core, it provides the same
thing L4S does<br>
(a high-fidelity explicit congestion signal for the
sender), but with<br>
much cleaner semantics that can be incrementally added to
congestion<br>
controls that people are already using.<br>
<br>
Granted, it still remains to be seen whether SCE in
practice can match<br>
the results of L4S, and L4S was here first. But it seems
to me L4S comes<br>
with some problems that have not yet been examined, and
that are nicely<br>
dodged by a SCE-based approach.<br>
<br>
If L4S really is as good as they seem to think, I could
imagine getting<br>
behind it, but I don't think that's proven yet. I'm not
certain, but<br>
all the comparative analyses I remember seeing have been
from more or<br>
less the same team, and I'm not convinced they don't have
some<br>
misaligned incentives of their own.<br>
<br>
I understand a lot of work has gone into L4S, but this
move to jump it<br>
from interesting experiment to de-facto standard without a
more critical<br>
review that digs deeper into some of the potential
deployment problems<br>
has me concerned.<br>
<br>
If it really does turn out to be good enough to be
permanent, I'm not<br>
opposed to it, but I'm just not convinced that it's
non-harmful, and my<br>
default position is that the cleaner solution is going to
be better in<br>
the long run, if they can do the same job.<br>
<br>
It's not that I want it to be a fight, but I do want to
end up with the<br>
best solution we can get. We only have the one internet.<br>
<br>
Just my 2c. <br>
<br>
-Jake<br>
<br>
<br>
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<br>
-- <br>
<div class="gmail_signature" dir="ltr">
<div dir="ltr">New postal address:
<div>Google<br>
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<br>
<pre class="moz-signature" cols="72">--
________________________________________________________________
Bob Briscoe <a class="moz-txt-link-freetext" href="http://bobbriscoe.net/">http://bobbriscoe.net/</a></pre>
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