[Bloat] My (controversial) position paper on TCP

David Collier-Brown davec-b at rogers.com
Mon Mar 18 18:03:56 EDT 2019

Hey Dave, are you available for consulting gigs in Canada?

In my latest incarnation, I'm doing on-line auctions in < 120 
milliseconds, with at least one round trip to ~10 bidders, and I suspect 
we never get out of slow start.

I wonder if I can make a case that this is significant, and if you can 
suggest a consulting gig to fix it??? Centos on Intel, in this case.


On 2019-03-18 6:04 a.m., Dave Taht wrote:
> I'm sure this would be controversial, and at the moment I'm focused on
> testing some sce.h +fq_codel code for freebsd. I'll slam it into the
> ecn-sane website at some point.
> ...
> TCP is done. It's baked. It's finished. There is very little left we
> can do to improve it, and we should move on to improving new
> transports such as QUIC which have option space left. [1]
> Ever since https://tools.ietf.org/html/rfc6013 failed in favor of tcp
> fast open, I'd given up on tcp. It was a lousy rfc in that it didn't
> make clear its best use case was in giving dns servers a safe and fast
> way to use tcp, which would have helped reduce the amount of DDOS and
> reflection attacks, speed things up, and so on. It wasn't until I had
> a long discussion with paul vixie about this use case and worldwide
> problem with dns that I understood it's intent to add a good stable
> 3way handshake to dns was so good.... and by then it was too late.
> Instead, tcp fast open was standardized for a limited (IMHO) use case
> of making web traffic better. Web traffic has a terrible interaction
> with TCP, in that it tends to start up 6 or more simultaneous
> connections and slam the link with stuff in slow start simultaneously.
> Others standards that I opposed, like IW10 [2], also got adopted, and
> we (as part of the cake project) tried to get an AQM (cobalt) that
> responded faster to stuff in slow start. Which we succeeded at, and
> that paper is progress, but it's still not good enough.
> It makes me really crazy that all the other TCP researchers in the
> world tend to focus on improving TCP behavior in congestion avoidance
> mode - because the statistics are easy to measure! - instead of
> focusing on the 95% of flows that never manage to get out of slow
> start. Yea, it's hard to look at slow start. That's why we've been
> looking at it hard for 5+ years in the bufferbloat project - trying to
> get linux, flent, irtt, to be able to look in detail at sub 4ms
> intervals, among other things.
> There are so many other problems with TCP as a transport - it requires
> a stateful firewall for ipv4 + nat, and more stuff than I have time to
> go into today...
> One item off that long list:
> QUIC and Wireguard have a really nice 0 RTT reconnect over crypto
> time. I like it a lot. I have not had time to poke much into the DOH
> working group at the ietf, but my take on it was that we needed to
> make dns better, not replace it.
> [1] Up until about 6 months ago, I really felt that we couldn't
> improve tcp anymore. DCTCP was a dead end. However the SCE idea makes
> it possible to have selectable behaviors on the receiver side -
> notably, a low priority background transport application (for
> backups/bittorrent) can merely overreact to SCE markings by sending
> back ECE to the tcp sender thus getting them to back off faster and be
> invisible to other applications. Or something more complicated (in
> slow start phase) could be used. ACCUECN also seemed feasible. And
> dctcp like approaches to another transport than tcp seemed very
> feasible.
> But to me, the idea was that we'd improve low latency applications
> such as gaming and videoconferencing and VR/AR with SCE, not "fix"
> tcp, overall. Goal in life was to have 0 latency for all flows - if it
> cost a little bandwidth, fine - 0 latency. The world is evolving to
> "enough" bandwidth for everything, but still has too much latency. The
> whole l4s thing conflating the benefits low latency with an
> ecn-enabled tcp has makes me crazy because it isn't true, as loss is
> just fine on most paths - lordy I don't want to go into that here,
> today. loss hurts gaming and videoconferencing more.
> Another ietf idea that makes me crazy is the motto of "no host
> changes" in homenet, and "dumb endpoints" - when we live in an age
> where we have quad cores and AI coprocessors in everybody's hands.
> The whole QUIC experiment shows what can be done when you have smart
> endpoints, along with a network that is as dumb as possible, but no
> dumber.
> [2] https://tools.ietf.org/html/draft-gettys-iw10-considered-harmful-00
> I would prefer folk wrote a position paper for ecn-sane rather than
> endlessly discuss this over email. that said, I needed to get this out
> of my system.
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain

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