How do I find out / calculate the SNR on VDSL2?

[g67575]

I have an Asus DSL-N16 router + modem, and I'd like to know what the SNR of my VDSL2 connection is.

The SNR in ADSL can be used to help calculate the 'max rate' (max connection speed) I believe, on ADSL connections. This is worked out by subtracting the Attenuation from the SNR of the line.

My downstream connection has been around 10mbps lower than the reported max rate, for several months now, so I'm curious if the reported max rate is accurate.

Or, is there a separate SNR for each VDSL2 band? As can be seen below:

 

[g67575]

The other thing that occurs to be, is that most lines will use an SNR Margin of 6dB, which I think is set by the equipment at the exchange or FTTC cabinet.

Normally, if I don't tamper with any SNR Margin settings, my line defaults to approx. 6dB, across all VDSL2 bands, which I assume it adjusts the line rate to ensure an SNR margin of ~6dB, whenever the modem syncs.

I've increased this to 8db, this reduces the FEC / CRC error rate below 100 per day (there's good reason to think this would result in higher sync speeds, because of how the DLM system works in the long term).

Anyway, I think the SNR might just be the difference between the reported SNR Margin, and Openreach's Target SNR Margin of 6DB (to complicate things, this can be set lower on some lines). My router reports an SNR Margin of 7.7-7.6 dB.

So, in my case, this would be an SNR of 1.6-1.7dB, depending on the Downstream band (D1, D2, and D3 on my line).

Or, the SNR might just be the lowest point on the graph shown above, so around 11dB.