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

Thu Aug 28 12:52:58 EDT 2014

Regarding AQM in North American HFC deployments-

I also can't speak for individual Service Providers, but Greg was being modest and the following may be interesting.

The most recent DOCSIS 3.1 specs calls for AQM in the CMTS. It specifically calls for a specific variant of  PIE that is designed with the DOCSIS MAC layer in mind. The DOCSIS 3.0 spec is also being amended to require AQM. Both specs also have recommendations to include AQM in the Cable Modems that can be turned on in the HFC network.

See http://tools.ietf.org/html/draft-white-aqm-docsis-pie-00 for more details.

bvs

[http://www.cisco.com/web/europe/images/email/signature/logo05.jpg]

Bill Ver Steeg
Distinguished Engineer
Cisco Systems

From: bloat-bounces at lists.bufferbloat.net [mailto:bloat-bounces at lists.bufferbloat.net] On Behalf Of Greg White
Sent: Thursday, August 28, 2014 12:36 PM
To: Jerry Jongerius; 'Rich Brown'
Cc: bloat at lists.bufferbloat.net
Subject: Re: [Bloat] The Dark Problem with AQM in the Internet?

And again, AQM is not causing the problem that you observed.  As Jonathan indicated, it would almost certainly make your performance better.    I can't speak for Comcast, but AFAIK they are on a path to deploy AQM.  If their customers start raising FUD that could change.

TCP requires congestion signals.  In the vast majority of cases today (and for the foreseeable future) those signals are dropped packets.  Going on a witch hunt to find the evildoer that dropped your packet is counter productive.  I think you should instead be asking "why didn't you drop my packet earlier, before the buffer got so bloated and power boost cut the BDP by 60%?"

-Greg

From: Jerry Jongerius <jerryj at duckwae.com<mailto:jerryj at duckwae.com>>
Date: Thursday, August 28, 2014 at 10:20 AM
To: 'Rich Brown' <richb.hanover at gmail.com<mailto:richb.hanover at gmail.com>>
Cc: "bloat at lists.bufferbloat.net<mailto:bloat at lists.bufferbloat.net>" <bloat at lists.bufferbloat.net<mailto:bloat at lists.bufferbloat.net>>
Subject: Re: [Bloat] The Dark Problem with AQM in the Internet?

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<mailto: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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