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From: Rich Brown <richb.hanover@gmail.com>
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Date: Thu, 28 Aug 2014 10:39:12 -0400
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To: Jerry Jongerius <jerryj@duckware.com>
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Cc: bloat@lists.bufferbloat.net
Subject: Re: [Bloat] The Dark Problem with AQM in the Internet?
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Hi Jerry,

> AQM is a great solution for bufferbloat.  End of story.  But if you =
want to track down which device in the network intentionally dropped a =
packet (when many devices in the network path will be running AQM), how =
are you going to do that?  Or how do youpropose to do that?

Yes, but... I want to understand why you are looking to know which =
device dropped the packet. What would you do with the information?

The great beauty of fq_codel is that it discards packets that have dwelt =
too long in a queue by actually *measuring* how long they've been in the =
queue.=20

If the drops happen in your local gateway/home router, then it's =
interesting to you as the "operator" of that device. If the drops happen =
elsewhere (perhaps some enlightened ISP has installed fq_codel, PIE, or =
some other zoomy queue discipline) then they're doing the right thing as =
well - they're managing their traffic as well as they can. But once the =
data leaves your gateway router, you can't make any further predictions.

The SQM/AQM efforts of CeroWrt/fq_codel are designed to give near =
optimal performance of the *local* gateway, to make it adapt to the =
remainder of the (black box) network. It might make sense to instrument =
the CeroWrt/OpenWrt code to track the number of fq_codel drops to come =
up with a sense of what's 'normal'. And if you need to know exactly =
what's happening, then tcpdump/wireshark are your friends.=20

Maybe I'm missing the point of your note, but I'm not sure there's =
anything you can do beyond your gateway. In the broader network, =
operators are continually watching their traffic and drop rates, and =
adjusting/reconfiguring their networks to adapt. But in general, it's =
impossible for you to have any sway/influence on their operations, so =
I'm not sure what you would do if you could know that the third router =
in traceroute was dropping...

Best regards,

Rich

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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Diso-8859-1"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Hi =
Jerry,<div><div><div><br></div><blockquote type=3D"cite"><div =
style=3D"margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: =
Calibri, sans-serif; font-style: normal; font-variant: normal; =
font-weight: normal; letter-spacing: normal; line-height: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;">AQM<span =
class=3D"Apple-converted-space">&nbsp;</span><b>is</b><span =
class=3D"Apple-converted-space">&nbsp;</span>a great solution for =
bufferbloat.&nbsp; End of story.&nbsp; But if you want to track down =
which device in the network intentionally dropped a packet (when many =
devices in the network path will be running AQM), how are<span =
class=3D"Apple-converted-space">&nbsp;</span><i>you</i><span =
class=3D"Apple-converted-space">&nbsp;</span>going to do that?&nbsp; Or =
how do<span class=3D"Apple-converted-space">&nbsp;</span><i>you</i>propose=
 to do that?</div></blockquote><div><br></div>Yes, but... I want to =
understand why you are looking to know which device dropped the packet. =
What would you do with the information?</div><div><br></div><div>The =
great beauty of fq_codel is that it discards packets that have dwelt too =
long in a queue by actually *measuring* how long they've been in the =
queue.&nbsp;</div><div><br></div><div>If the drops happen in your local =
gateway/home router, then it's interesting to you as the "operator" of =
that device. If the drops happen elsewhere (perhaps some enlightened ISP =
has installed fq_codel, PIE, or some other zoomy queue discipline) then =
they're doing the right thing as well - they're managing their traffic =
as well as they can. But once the data leaves your gateway router, you =
can't make any further predictions.</div><div><br></div><div>The SQM/AQM =
efforts of CeroWrt/fq_codel are designed to give near optimal =
performance of the *local* gateway, to make it adapt to the remainder of =
the (black box) network. It might make sense to instrument the =
CeroWrt/OpenWrt code to track the number of fq_codel drops to come up =
with a sense of what's 'normal'. And if you need to know exactly what's =
happening, then tcpdump/wireshark are your =
friends.&nbsp;</div><div><div><br></div><div>Maybe I'm missing the point =
of your note, but I'm not sure there's anything you can do beyond your =
gateway. In the broader network, operators are continually watching =
their traffic and drop rates, and adjusting/reconfiguring their networks =
to adapt. But in general, it's impossible for you to have any =
sway/influence on their operations, so I'm not sure what you would do if =
you could know that the third router in traceroute was =
dropping...</div><div><br></div><div>Best =
regards,</div><div><br></div><div>Rich</div></div></div></body></html>=

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