
BBR: Congestion-Based Congestion Control - alanfranzoni
http://queue.acm.org/detail.cfm?id=3022184
======
r1ch
This sounds amazing. Poor TCP congestion control algorithms have long been the
limiting factor of today's broadband connections never reaching their
potential speed. It looks like this was already patched into the kernel for
those interested:
[https://lwn.net/Articles/701149/](https://lwn.net/Articles/701149/) \- can't
wait to experiment with this!

------
akshayn
This is a delay-based scheme; it is unlikely to work well if competing with a
drop-based aggressive scheme like TCP Cubic.

As a result, while BBR is fantastic for deployment e.g. in Google's private
WAN, it's unclear how well it would do in the Internet, and initial
experiments are not promising [1].

[1] [http://www.ietf.org/mail-
archive/web/tsvwg/current/msg14798....](http://www.ietf.org/mail-
archive/web/tsvwg/current/msg14798.html)

~~~
tedd4u
I think that's a risk for sure -- if it can't compete with Cubic, what will
the user experience be like? The authors note that it's still actively being
researched. They do cite encouraging public internet deployment test results
though:

"BBR is being deployed on Google.com and YouTube video servers. Google is
running small-scale experiments in which a small percentage of users are
randomly assigned either BBR or CUBIC. Playbacks using BBR show significant
improvement in all of YouTube's quality-of-experience metrics, possibly
because BBR's behavior is more consistent and predictable. BBR only slightly
improves connection throughput because YouTube already adapts the server's
streaming rate to well below BtlBw to minimize bufferbloat and rebuffer
events. Even so, BBR reduces median RTT by 53 percent on average globally and
by more than 80 percent in the developing world."

Regarding deployment: between Apple and Samsung they control 75% of mobile all
mobile Internet traffic [1]. So with only two vendors deploying, we could see
a very fast pace of adoption. Given there are now more mobile users than
desktop users [2] and that mobile media time is now exceeding desktop media
streaming time [2] it seems like mobile Internet traffic could be the majority
(would love to know if anyone can find better stats on this, i.e. % of
Internet traffic mobile vs desktop). A decade ago

But yes on private-backbone use cases like Google (and other companies with a
lot of private fiber networks) are likely the most immediate adopters it could
easily save millions a year -- 133x throughput (!)

"Manually raising the receive buffer on one US-Europe path caused BBR
immediately to reach 2 Gbps, while CUBIC remained at 15 Mbps—the 133x relative
improvement predicted by Mathis et al."

[1] [http://marketingland.com/report-apple-iphone-drives-half-
mob...](http://marketingland.com/report-apple-iphone-drives-half-mobile-
internet-traffic-111129) [2] [https://hostingfacts.com/internet-facts-
stats-2016/](https://hostingfacts.com/internet-facts-stats-2016/)

~~~
akshayn
Right, it's unclear however the context of the YouTube results. If they
evaluated on links bottlenecked at the edge at 128Kbps, BBR isn't really
competing with Cubic anywhere.

This isn't to say that BBR is "bad" \- just that it's not mentioned what the
"quality of experience metrics" are. They're obviously not getting better
throughput, and the only way they can improve delay is if the edge buffer is
overprovisioned (i.e. bufferbloat). In that case (edge bottleneck, relatively
low BW), I'd be interested to see a comparison to Sprout[1].

[1]
[https://www.usenix.org/system/files/conference/nsdi13/nsdi13...](https://www.usenix.org/system/files/conference/nsdi13/nsdi13-final113.pdf)

------
X86BSD
I believe I read yesterday this is being committed soon to FreeBSD head.

