[Cake] [Bloat] active sensing queue management

Alan Jenkins alan.christopher.jenkins at gmail.com
Fri Jun 12 09:00:33 EDT 2015

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 :).

- 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).

> 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

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