I can confirm it's nothing in the house and the phone was not used during these blips. Anyway, it's been dropped to 4 dB now so obviously it's not causing a problem.

A reduction in the SNR margin will only cause throughput issues if there is an increase in uncorrectable errors requiring a retransmit. It would be best to monitor error rates to see if there is a correlation.

As for what's causing fluctuations, both long and short term, then the former is normally down to things like atmospherics whilst short term fluctuation cans be caused by any number of sources of EMF.

I understand that, there were no errors but the amount G.INP retransmits going on would suggest the reduction in throughput.

In reply to a post by WilliamGrimsley:

I understand that, there were no errors but the amount G.INP retransmits going on would suggest the reduction in throughput.

You really need to stop obsessing about your connection.

It may come over that way, but I'm not.

g.inp retransmissions are errors, just corrected ones, so if that is getting very high it could affect throughput to some extent, but high is the operative word. It would be transparent to the IP layer, so would not cause the sort of problems you see with packet loss, so it would never be that marked.

I already know that (that's meant in a positive not targeting way).

Just looking into your history you mentioned that you use ethernet power line adapters they are not the cleanest way to connect to a modem it has drawbacks increased FEC errors which is extra noise and can only guess that is what is causing your upstream to bounce from g.inp to fastpath and downstrean to sometimes enter the interleaving profile.

Would get rid of any ethernet powerline adapters and see how your line performs over 2 weeks.

I wish I didn't have to use them, but unfortunately we have to for our BT TV service.

NTE shift?