[Bloat] The Dark Problem with AQM in the Internet?

[Jerry Jongerius]

It add accountability.  Everyone in the path right now denies that they
could possibly be the one dropping the packet.

 

If I want (or need!) to address the problem, I can't now.  I would have to
make a change and just hope that it fixed the problem.

 

With accountability, I can address the problem.  I then have a choice.  If
the problem is the ISP, I can switch ISP's.  If the problem is the mid-level
peer or the hosting provider, I can test out new hosting providers.

 

- Jerry

 

 

 

From: Rich Brown [mailto:richb.hanover at gmail.com] 
Sent: Thursday, August 28, 2014 10:39 AM
To: Jerry Jongerius
Cc: Greg White; Sebastian Moeller; bloat at lists.bufferbloat.net
Subject: Re: [Bloat] The Dark Problem with AQM in the Internet?

 

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. 

 

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. 

 

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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