> On Aug 21, 2019, at 09:50, Sebastian Gottschall
> <[email protected]> wrote:
>
>>> i have seen this already. out plan here is that the user specifies the
>>> internet connection type like vdsl2, cable, whatever in case of cake which
>>> then will be used
>>> as argument
>> Good goal, that also is theoretically well supported by cake with its
>> multitude of encapsulation/overhead realated keywords. Unfortunately reality
>> is not as nice and tidy as this collection of keywords implies, There are 8
>> keywords for ATM/AAL5 based encapsulations (ADSL, ADSL2, ADSL2+, ...), 2 for
>> VDSL2, 1 for DOCSIS, 1 for ethernet, for a total of 12 that all can be
>> combined with one or more VLAN-tag keywords, for a total of 24 to 36
>> combinations. (And these are not even exhaustive, as e.g. the use of ds-lite
>> can increase the per-packet overhead for IPv4 packets by another 20 bytes).
>> Ideally one would just empirically measure the effective overhead and
>> use the "overhead NN mpu NN" keywords instead, but that has issues as
>> measuring overhead empirically is simply hard... The best bet would be to
>> leverage BEREC to require ISPs to explicitly inform their customers of the
>> effective gross-rates and applicable overheads for each link, but I am not
>> holding my breath. Over at
>> https://openwrt.org/docs/guide-user/network/traffic-shaping/sqm we tried to
>> give simplified instructions for setting the overheads for different access
>> technologies, but these are not guaranteed to fit everybody (not even most
>> users, as we have no numbers about the relative distributions of the
>> different encapsulation options).
>>
>> Best Regards
>> "another" Sebastian
>
> as i said. i just started. lets see if i can find a better solution or a
> clever way of auto detecting/measuring the overhead
If you do find a clever and fat way, please let me know ;). The best I
came up with only works for ATM/AAL5 and is neither clever, automated or fast
is at https://github.com/moeller0/ATM_overhead_detector (which has the
advantage of also confirming ATM/AAL5-quantisation). I have some ideas about
how to deduce overhead generically but these require very precise measurements
of maximum goodput for different packet sizes and even less fit for general
consumption that the atm stuff.
Best Regards
Sebastian
>
> Sebastian
>
>>
>>
>>
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