[Cake] [Bloat] active sensing queue management

Daniel Havey dhavey at gmail.com
Fri Jun 12 10:35:23 EDT 2015

On Fri, Jun 12, 2015 at 6:00 AM, Alan Jenkins
<alan.christopher.jenkins at gmail.com> wrote:
> On 12/06/15 02:44, David Lang wrote:
>> On Thu, 11 Jun 2015, Sebastian Moeller wrote:
>>> On Jun 11, 2015, at 03:05 , Alan Jenkins
>>> <alan.christopher.jenkins at gmail.com> wrote:
>>>> On 10/06/15 21:54, Sebastian Moeller wrote:
>>>> One solution would be if ISPs made sure upload is 100% provisioned.
>>>> Could be cheaper than for (the higher rate) download.
>>>     Not going to happen, in my opinion, as economically unfeasible for a
>>> publicly traded ISP. I would settle for that approach as long as the ISP is
>>> willing to fix its provisioning so that oversubscription episodes are
>>> reasonable rare, though.
>> not going to happen on any network, publicly traded or not.
> Sure, I'm flailing.  Note this was in the context of AQSM as Daniel
> describes it.  (Possibly misnamed given it only drops.  All the queuing is
> "underneath" AQSM, "in the MAC layer" as the paper says :).
Noooooooooo!  I am a huge supporter of ECN.  ECE Everywhere!  I'm sure
I wrote "mark/drop" in the paper.  I might have dyslexically written
"drop/mark", but, if I ever gave the impression then I categorically
deny that right now and till forever.  ECN everywhere :^)

> - AQSM isn't distinguishing up/down bloat.  When it detects bloat it has to
> limit both directions in equal proportion.
> => if there is upload contention (and your user is uploading), you may hurt
> apps sensitive to download bandwidth (streaming video), when you don't need
> to.
> What would the solutions look like?
> i) If contention in one direction was negligible, you could limit the other
> direction only.  Consumer connections are highly asymmetric, and AQSM is
> only measuring the first IP hop.  So it's more feasible than 100% in both
> directions.  And this isn't about core networks (with larger statistical
> universes... whether that helps or not).
> I'm sure you're right and they're not asymmetric _enough_.
> ii) Sebastian points out if you implement AQSM in the modem (as the paper
> claims :p), you may as well BQL the modem drivers and run AQM.  *But that
> doesn't work on ingress* - ingress requires tbf/htb with a set rate - but
> the achievable rate is lower in peak hours. So run AQSM on ingress only!
> Point being that download bloat could be improved without changing the other
> end (CMTS).
This is pretty cool.  I had not considered BQL (though Dave and Jim
were evangelizing about it at the time :).  This solves the
upload/download problem which I was not able to get past in the paper.
BQL on the egress and ASQM for the ingress.  BQL will make sure that
the upload is under control so that ASQM can get a good measurement on
the download side.  Woot!  Woot!  Uncooperative ISP problem solved!

BTW...Why doesn't BQL work on the ingress?

>> The question is not "can the theoretical max of all downstream devices
>> exceed the upstream bandwidth" because that answer is going to be "yes" for
>> every network built, LAN or WAN, but rather "does the demand in practice of
>> the combined downstream devices exceed the upstream bandwidth for long
>> enough to be a problem"
>> it's not even a matter of what percentage are they oversubscribed.
>> someone with 100 1.5Mb DSL lines downstream and a 50Mb upstream (30% of
>> theoretical requirements) is probably a lot worse than someone with 100 1G
>> lines downstream and a 10G upstream (10% of theoretical requirements)
>> because it's far less likely that the users of the 1G lines are actually
>> going to saturate them (let alone simultaniously for a noticable timeframe),
>> while it's very likely that the users of the 1.5M DSL lines are going to
>> saturate their lines for extended timeframes.
>> The problem shows up when either usage changes rapidly, or the network
>> operator is not keeping up with required upgrades as gradual usage changes
>> happen (including when they are prevented from upgrading because a peer
>> won't cooperate)
>> As for the "100% provisioning" ideal, think through the theoretical
>> aggregate and realize that before you get past very many layers, you get to
>> a bandwidh requirement that it's not technically possible to provide.
>> David Lang

Yuppers!  Dave is right.  The FCC studies (especially the 80/80 study
out of UNC) from 2010 - 2014 (footnoted in the paper) indicate that
during peak hours it is quite common for an ISP not to provide 100% of
the rated throughput.  In fact in 2014 it indicates that a full on 50%
of the ISPs measured provided less than 100%.  The 100% all the time
goal is unreasonable because it implies too much waste.  Many ISPs get
to 90% or above even during peak hours.  This is good!  We could live
with that :)  Providing that last 10% would mean that they would have
to provide for a lot of excess capacity that goes unused during
non-peak hours.  Wasteful.  That money should be allocated for more
important things like providing AQM for all or saving the planet or
something else. :^)

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