Help untangling CAKE settings for FTTH

[Thibaut]

Hi Sebastian,

> Le 17 nov. 2022 à 10:50, Sebastian Moeller <moeller0 at gmx.de> a écrit :
> 
> Hi T.
> 
> 
> so taking your proposa under consideration I canged the section that threw you off course to read:
> 
> 
> 	• Ethernet with Overhead: SQM can also account for the overhead imposed by VDSL2 links - add 22 bytes of overhead (mpu 68). Cable Modems (DOCSIS) set both up- and downstream overhead to 18 bytes (6 bytes source MAC, 6 bytes destination MAC, 2 bytes ether-type, 4 bytes FCS), to allow for a possible 4 byte VLAN tag it is recommended to set the overhead to 18 + 4 = 22 (mpu 64). For FTTH the answer is less clear cut, since different underlaying technologies have different relevant per-packet-overheads; however underestimating the per-packet-overhead is considerably worse for responsiveness than (gently) overestimating it, so for FTTH set the overhead to 44 (mpu 84) unless there is more detailed information about the true overhead on a link available.
> 	• None: All shaping below the physical gross-rate of a link requires correct per-packet overhead accounting to be precise, so None is only useful if approximate shaping is sufficient, say if you want to clamp a guest network to at best ~50% of the available capacity or similar tasks, but even then configuring an approximate correct per-packet-overhead is recommended (overhead 44 (mpu 84) is a decent default to pick).
> 
> 
> I hope this is explicit enough.

Yes this looks a lot better, thank you.

Although I must confess that it certainly feels counter-intuitive that for ethernet (and FTTH) we suggest a higher overhead than e.g. VDSL2/cable (which themselves run off an ethernet interface).

I would also like to see some info about ppp vs ethernet interface in there (matching your previous email): unless you beat me to it I will add it.
I also think the « details » page needs to be reformatted a bit, it’s very dense and relevant info is all over the place and not very well organized. I’ll try to get around improving that.

Thanks