Hi

Does anyone know how adjusting the SNR noise margin on a vigor 130 on VDSL2 works ?

Ive lowered mine to 3db and seen a good increase in synch speed, yet a Openreach 'expert' states that this is not possible.

Modem is working well and I access the CLI by putting a switch on the WAN ethernet cable to the netgear router

The openreach 'expert' is wrong. The Openreach supplied modems don't allow SNR tweaking but 3rd party ones, including the Vigor 130, do. Depending on the equipment (DSLAM) in your local cabinet you will have a default SNR margin set, usually either 3 or 6dB, and your modem will negotiate a sync rate that hits this target. If you have cabinet equipment that sets a default of 6dB and you have a modem capable of tweking it's SNR margin then you can indeed improve your speeds albeit with a potential for more disconnects as the SNR creeps lower to 0 due to fluctuations throughout the day.

I have adjusted the snr noise margin on my 130 and I believe draytek first, but I wondered if anyone knows the actual negotiation process between DLM and the modem. I imagine it sends squirts on the DS and the modem replies with errors, power at input etc and visa versa on the US.

The 'expert' also states that my 130 isn't telling me the truth because it's reporting g.inp active on the downstream despite being connected to an ECI cabinet

Don't you lov 'experts'

Maybe your cabinet has G.INP rolled out:

UPDATE 1st Feb 2018

We understand that so far the ECI Retransmission Trial has migrated around 600,000 lines and the official rollout is about to commence across their estate. The xdB (3dB profile) has also been successfully applied to some ECI lines.

https://www.ispreview.co.uk/index.php/2017/12/openreach-pause-uk-trial-g-inp-fix-eci-fttc-broadband-cabs.html

I have had to set my SNR to 6dB due to the draytek failing to stay online since they moved my connection to a 3dB. I have the draytel vigor 2860n 45 days now on 6 dB yet couldn't get a day on 3dB.