> On Aug 20, 2019, at 18:47, Sebastian Gottschall
> <[email protected]> wrote:
>
>
> Am 20.08.2019 um 18:24 schrieb Dave Taht:
>> On Tue, Aug 20, 2019 at 5:09 AM Sebastian Gottschall
>> <[email protected]> wrote:
>>> [...]
>>
>> If I had any one principal request it would be to make sure the dd-wrt
>> gui (if one is made) exposes the link layer parameters. Getting the
>> framing wrong is about the biggest error I see in the deployment:
>> https://www.youtube.com/watch?v=LjJW_s5gQ9Y
> 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
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