Good to hear. It’s getting to the limit of my understanding now but after talking with others, I kind of understand mpu.
The linux kernel (which obviously cake runs on) has to at a bare minimum keep track of a 21 byte packet (20 byte header and 1 byte payload) to function. However once you introduce layer 2 ethernet frames this packet goes to 64 at the bare minimum.
Note: The reason why 34 is correct is 6 for mac destination, 6 for mac source, 802.1q (our vlan tag) 4, ethertype of 2, FCS of 4, ptm itself is 4 (S, ck, PTM-FCS), protocol id is 2 (since pppoe authentication) and finally pppoe containing version code, session id etc of 6.
We take 80 as an mpu because vdsl2 covers the l2 ethernet frame so it can be assigned the whole minimum payload size of 46. However we still need to account for the whole actual l2 ethernet frame so our 34 + 46 = 80.
However, all of this mpu stuff can be considered a red herring. It’s nice to get close (80 does seem strong) but in reality a minimum packet size is fruitless. It would only really show with super small ACK packets. Something that isn’t really going to happen much.
I did run tests and usually I was +2 ms on waveform. Now I was able to get +0 ms on waveform so seems like something did change.
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