[Cerowrt-devel] [Bloat] better business bufferbloat monitoring tools?

Jim Gettys jg at freedesktop.org
Wed May 13 11:30:40 EDT 2015

On Wed, May 13, 2015 at 9:20 AM, Bill Ver Steeg (versteb) <versteb at cisco.com
> wrote:

> Time scales are important. Any time you use TCP to send a moderately large
> file, you drive the link into congestion. Sometimes this is for a few
> milliseconds per hour and sometimes this is for 10s of minutes per hour.
> For instance, watching a 3 Mbps video (Netflix/YouTube/whatever) on a 4
> Mbps link with no cross traffic can cause significant bloat, particularly
> on older tail drop middleboxes.  The host code does an HTTP get every N
> seconds, and drives the link as hard as it can until it gets the video
> chunk. It waits a second or two and then does it again. Rinse and Repeat.
> You end up with a very characteristic delay plot. The bloat starts at 0,
> builds until the middlebox provides congestion feedback, then sawtooths
> around at about the buffer size. When the burst ends, the middlebox burns
> down its buffer and bloat goes back to zero. Wait a second or two and do it
> again.

​It's time to do some packet traces to see what the video providers are
doing.  In YouTube's case, I believe the traffic is using the new sched_fq
qdisc, which does packet pacing; but exactly how this plays out by the time
packets reach the home isn't entirely clear to me. Other video
providers/CDN's may/may not have started generating clues.

Also note that so far, no one is trying to pace the IW transmission at all.

> You can't fix this by adding bandwidth to the link. The endpoint's TCP
> sessions will simply ramp up to fill the link. You will shorten the
> congested phase of the cycle, but TCP will ALWAYS FILL THE LINK (given
> enough time to ramp up)

​That has been the behavior in the past, but it's no longer safe to
presume​ we should tar everyone with the same brush, rather, we should do a
bit of science, and then try to hold people's feet to the fire that do not
"play nice" with the network.

​Some packet captures in the home can easily sort this out.



> The new AQM (and FQ_AQM) algorithms do a much better job of controlling
> the oscillatory bloat, but you can still see ABR video patterns in the
> delay figures.
> Bvs
> -----Original Message-----
> From: bloat-bounces at lists.bufferbloat.net [mailto:
> bloat-bounces at lists.bufferbloat.net] On Behalf Of Dave Taht
> Sent: Tuesday, May 12, 2015 12:00 PM
> To: bloat; cerowrt-devel at lists.bufferbloat.net
> Subject: [Bloat] better business bufferbloat monitoring tools?
> One thread bothering me on dslreports.com is that some folk seem to think
> you only get bufferbloat if you stress test the network, where transient
> bufferbloat is happening all the time, everywhere.
> On one of my main sqm'd network gateways, day in, day out, it reports
> about 6000 drops or ecn marks on ingress, and about 300 on egress.
> Before I doubled the bandwidth that main box got, the drop rate used to be
> much higher, and a great deal of the bloat, drops, etc, has now moved into
> the wifi APs deeper into the network where I am not monitoring it
> effectively.
> I would love to see tools like mrtg, cacti, nagios and smokeping[1] be
> more closely integrated, with bloat related plugins, and in particular, as
> things like fq_codel and other ecn enabled aqms deploy, start also tracking
> congestive events like loss and ecn CE markings on the bandwidth tracking
> graphs.
> This would counteract to some extent the classic 5 minute bandwidth
> summaries everyone looks at, that hide real traffic bursts, latencies and
> loss at sub 5 minute timescales.
> mrtg and cacti rely on snmp. While loss statistics are deeply part of
> snmp, I am not aware of there being a mib for CE events and a quick google
> search was unrevealing. ?
> There is also a need for more cross-network monitoring using tools such as
> that done by this excellent paper.
> http://www.caida.org/publications/papers/2014/measurement_analysis_internet_interconnection/measurement_analysis_internet_interconnection.pdf
> [1] the network monitoring tools market is quite vast and has many
> commercial applications, like intermapper, forks of nagios, vendor specific
> producs from cisco, etc, etc. Far too many to list, and so far as I know,
> none are reporting ECN related stats, nor combining latency and loss with
> bandwidth graphs. I would love to know if any products, commercial or open
> source, did....
> --
> Dave Täht
> Open Networking needs **Open Source Hardware**
> https://plus.google.com/u/0/+EricRaymond/posts/JqxCe2pFr67
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