Sorry once again to everyone following this or finding via Google search… the plot thickens as they say. I now however have 100% values for wan packet overhead and mpu for VDSL2 PPPoE PTM (FTTC) with vlan 101 tag in UK.
I was going to just edit my above posts with the final info but hopefully people can look back and see the journey and the reasoning. I guess the point is don’t be afraid to try and experiment till things fall into place!
For wan packet overhead it is still 34 so that’s good. About mpu however:
My last post was very close… agonizingly so. I didn’t factor in a very crucial change to the ethernet frame: https://en.wikipedia.org/wiki/Ethernet_frame#Payload
The important part: “the minimum payload is 42 octets when an 802.1Q tag is present and 46 octets when absent”.
So what does this actually mean for us? Well since you actually “lose” 4 bytes in the ethernet payload by having the 101 tag, you already account for the vlan tag in the minimum amount at 64. So thus you just need to add 4 bytes for ptm transmission.
Thus the final (and will not change) number for mpu is 68. If you want to see how the Asus router page should look:
Also some extra info on why Mode should be Normal and not PTM even though we have PTM service:
If you set the PTM mode, there is an additional calculation by cake for every packet in which it accounts for the 64/65 encapsulation. It makes much more sense to just account for this in the bandwidth number you supply to cake (in theory slightly less cpu load which is great for less powerful soc). This means 98.4% (64/65).
So e.g. above screenshot if my 90% upload bandwidth number is 10 then I should supply cake with 9.84.
Now the real fun begins when you move to FTTP… there is so many different technologies I would air on the side of caution and stick to the wiki guidelines as they are actually really solid to start with. FTTP should have a 44 wan packet overhead and an 84 mpu.
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