Info re the relationship between upload and download speeds.
Annex M pinches for upstream the lower frequencies usually used for downstream. If the line is relatively short there will be plenty of spare bin capacity higher up for the downstream to be unaffected, and there will also be the maximum upstream gain.
If the line is relatively long then the attenuation on the higher frequencies will be such that those higher frequency bins will be smaller so already fully utilised. The attenuation on the lower frequencies will also be high so the speed gain on Annex M is reduced. So it's win/win or lose/lose.
From observing O2/Be lines there seems to be a rule of thumb. Below an Annex A downstream sync of 16Mbps, forget about Annex M. It is likely to be lose/lose. Above 20Mbps Annex A downstream sync, almost certainly no effect on downstream but a significant gain in upstream. Win/win.
In-between, it depends on the individual user how valuable increased upstream speed is.
I haven't been looking out for error rates, but I would guess
that downstream rates would increase due to higher utilisation of the higher frequency bins. The scope for bit-swapping has to be reduced, with the knock-on effect of that. My guess could be garbage!
Hope that helps.
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