Two questions for my instruction.

[#1]

#1
Looking at the noise margin graphs in Routerstats I see that generally during the day hours the upstream fluctuates more frequently than that of the downstream, 30 in about 1.5 hours as against 3.
Does the high frequency of the changes have any significance? N.B. Generally they are +/- 1dB
#2
I understand PN cap upstream connection speed. Why is that and what benefit arises?

[#2]

1. My router on shows noise margin rounded to integers - I guess yours may be the same. It could be that the actual median value is something like 10.45db and it's only varying by 0.1db; routerstats would see this as flip-flopping between 10 and 11. I am sure it is nothing to worry about.
2. Theoretically on 21CN capping the upstream may give an improved downstream speed - I've not seen anything to prove/disprove that. If you are on ADSL2+ and are more than happy with your downstream I'd ask for the upstream to be uncapped.

[#3]

I'll mull that over.

rest  post withdrawn 17/6 am