[Bloat] [aqm] the cisco pie patent and IETF IPR filing

David Lang david at lang.hm
Wed Mar 4 04:42:45 EST 2015

On Wed, 4 Mar 2015, KK wrote:

> Date: Wed, 04 Mar 2015 01:01:19 -0800
> From: KK <kk at cs.ucr.edu>
> To: Vishal Misra <misra at cs.columbia.edu>, Dave Taht <dave.taht at gmail.com>
> Cc: "aqm at ietf.org" <aqm at ietf.org>, bloat <bloat at lists.bufferbloat.net>
> Subject: Re: [aqm] the cisco pie patent and IETF IPR filing
> I think a combination of PI/PIE/fq_codel with ECN would enable us
> a) be less dependent of the physical amount of buffering that is
> implemented on the intermediate devices
> b) allow us to use buffering for what it is meant to do - ride out
> transient variations in traffic, at points where there is a mismatch in
> available capacity

The question is how much of a burst should the buffer be able to handle? Right 
now buffers routinely hold 10+ seconds worth of traffic (and Dave T showed the 
airline system buffering 10+ MINUTES of traffic)

The problem is that if you buffer too much, you break the TCP link speed 
probing, and if you buffer even more you end up with the sender genrating a new 
packet to deliver while you still are buffering the old one.

Buffers need to hold less than one second worth of traffic, and emperical 
testing is showing that much less is desirable (Others can post more exact 
numbers, but I belive that somewhere between 1/100 of a second and 1/10 of a 
second is a reasonable range)

> c) allow us to support different types of links, including wireless lossy
> links

If a retry is fast and has a very high probability of succeding, then it may be 
worth holding it and doing a link-level retry. But the existing mess that is 
wifi is hardly a good example of this being the right thing to do in a congested 

David Lang

> d) as we wrote in the ECN RFC, allow even short-lived transfers to not
> suffer
> Thanks,

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