[Cerowrt-devel] Invisibility of bufferbloat and its remedies

Sebastian Moeller moeller0 at gmx.de
Tue Jun 19 19:32:43 EDT 2018


On June 19, 2018 10:34:07 PM GMT+02:00, valdis.kletnieks at vt.edu wrote:
>On Mon, 18 Jun 2018 18:46:18 -0700, Dave Taht said:
>> One of cake's "minor" features is the *perfect* defeat of the htb
>> based shaper in cable modems. If you know the set-rate on the modem,
>> you just set it to the same thing and get vastly superior performance
>> docsis 3.1, pie, or the sqm-scripts.
>Do we have a good cookbook on how to determine the set-rate?

With cable <DOCSIS 3.1 one can Snoop the management frames that will also carry the bandwidth definitions. Or with a compromised cable modem one could dump the DOCSIS config file that also contains that information. Or ask the ISP. Short of any of that one could run a umber of speedtests over a 24 hour period and simply extrapolate from the measured goodput to the required 'gross' DOCSIS shaper rate:

Measured TCP/ipv4 goodput * ((1518)/(1500-20-20)) = lower bound gross bandwidth estimate

DOCSIS employs a shaper to limit user's exceeding the contracted rates, that per DOCSIS standard assumes 1518 bytes of accountable raw frame size. Tangent that 1518 obviously is a 'lie' in that it does not include all per packet overhead in use on a DOCSIS carrier, but from an end-user perspective that difference is immaterial...

I realize that you probably wanted something simpler and more accurate, sorry to disappoint.

Best Regards

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>Cerowrt-devel at lists.bufferbloat.net

Sent from my Android device with K-9 Mail. Please excuse my brevity.

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