New Docsis 3.1 modem slow

[EwwwDavid]

I recently upgraded my internet service to 600mbps and was using a docsis 3.0 netgear modem without issue after the new service was initiated. I average between 400 - 450 mbps down which is at the top end of its capabilities. I recently purchased a new gigibit docsis 3.1 modem (netgear cm1200) and successfully provisioned/added to the account but immediately realized a drastic drop in download speed. At an absolute max I only receive between 30-40mbps down with a hard wired connection. I spoke to a rep a week or so ago who ran some line tests and said that everything “looked fine” and it was my wireless router was the culprit. After speaking with ASUS they assured me that this was an issue with the isp. I have since reverted to my old equipment as I need to work from home but would like to understand what I need to do to get the new equipment working properly.

[CCAndrew]

How are you testing speeds?

[EwwwDavid]

My testing speeds with the cm1200 were consistently between 30mbps - 40mbps down, and the upload speeds were about the same with my previous modem at 12mbps - 16mbps. I spoke to tier 2 tech support at Asus (my wireless router) and they said that the router and settings would have no issue accommodating but the issue appears to be something on the side of the isp or provisioning of the modem. This lead me to check the downstream signal strength since upstream was not effected. While using the old modem (cm500-100nas) and it appears to be a bit high (averaging between -9.2 and -12.2 dBmV on all channels down). All locked QAM256 channels x16 all SNR between 31.8 - 37.3. Could the signal strength be too far out of spec for the new Docsis 3.1 modem?

[CCAndrew]

The signal of -9 and -12 isn't high, it's too low and out of spec. SNR below 35 is out of spec. You didn't answer how you were testing speeds, just what they were. Is it hardwired from modem to PC(the correct way)? Or Modem to router to PC?

[EwwwDavid]

Yes - my mistake.. too LOW. And yes - speeds are being taken from a hard connection to the modem.

Thanks for your time btw!

[CCAndrew]

Can you compare levels at the point of entry? To compare levels that you get at the modem’s present location