[Cerowrt-devel] (no subject)

Sebastian Moeller moeller0 at gmx.de
Wed Jun 20 02:56:31 EDT 2018

Hi all,

> On Jun 20, 2018, at 01:32, Sebastian Moeller <moeller0 at gmx.de> wrote:
> Well,
> 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
>> to
>>> 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

Addendum: when running speedtests on cable for the purpose of estimating the "true" docsis shaper goodput one needs to take care to not be fooled by transient bandwidth allowances like powerboost but rather one needs to find the sustainable stable  maximum bandwidth; so fun all around. (And one needs to account for the correct overhead in the equation above so in the IPv6 case the (1500-20-20) needs to be replaced by (1500-40-20))

Best Regards

> 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
>        Sebastian
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