Problems with CM1150V upstream on Comcast Xfinity

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sleat wrote:

.... especially since the CMTS is calling for transmit levels between 46.8dBmV and 48.0dBmV. (That's with no splitters in the path, so I can't use my settop box.  If I add a splitter to be able to watch cable TV, the CMTS will call for another 3.5dBmV or so to make up for the splitter loss and I lose my internet service completely.)  ...

 

 Before I understood the root cause, I observed that if the ambient room temperature was lower than about 60deg F, the problems were worse.  More interestingly, upstream traffic will cause the chip to heat up, so there's a sort of bootstrap situation where you have to warm the chip up by generating some traffic, and as long as you keep a moderate level of upstream traffic going, things continue to work.  If you let it cool down, you have to start over.  At present, in addition to removing all splitters ... 

 

 

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sleat thanks for this research 

The one thing I am unlcear about is whether this only manifests itself in the Upload performance, or whether because of that upstream issue, it subsequently also cause download speed to suffer? 

I'm wondering if this is the issue I was having 

It had been working perfectly for almost a year 

Then my download speed would drop off to a crawl and it was always literally completely gone EVERY morning - my first indication as I was coming down stairs was that I could see my wireless doorbell camera controller was off-line before I even got to anything on a PC.  I found a power cycle on the modem would instantly bring it back only for the problem to repeat over the course of the day and ALWAYS every morning (overnight) it would be completely gone.  

The part about keeping traffic up helping (coupled with fact that overnight it was bad - my home has different HVAC systems for Living and bedrooms, so modem location is cooler during night and obviously internet not utilized either) - Aside from the power cycle, I would find a curiousity that if I forced several back to back speed tests it would come back (hence increasing the traffic component of your findings) 

Now - I had not seen your post at this stage, called Xfinity out and they checked all the lines to the street and all was good, they installed an Xfinity Modem and service has been perfect for a month now - so conclusively the Netgear Modem (as relates to my service) was a problem. After the first week of confirmed flawless performance  (vs before replacement of continuous problems EVERY day for two weeks) I contacted Netgear who were reluctant to exchange without having an online test done - I went through multiple layers of support, stamping my feet and refusing to go through the hurdles involved of having to have the Netgear re-activated by Xfinity when I had conclusive evidence that the Xfinity Modem worked and the Netgear did not. I finally got someone to agree and they generated RMA for exchange. 

Roll forward to having just received my replacement modem and I installed it yesterday 

Here are the numbers I am getting on the Upstream on the new modem (sorry I have none for the old one) 

It is running just over the range you indicated (all over 48, up to 49.5 for the highest one) - is this potential for issue? 

One additional thing I should add - after my modem was replaced with Xfinity even though all was working fine, I did some more investigation on the wiring - I have two TV boxes and there was a 3-way splitter installed; now it was an unbalanced splitter and found that the primary TV box had been connected to the -3.5 split (so the modem was on a -7 split); it did not give me any perfromance issues with the Xfinity modem, but I swapped them regardless so the Modem Cable is now on the -3.5 leg. 

So previously, it had been on the -7db connection (but had been from the outset) but the numbers below are reflected in a -3.5db connection.

Unfortunately I did not take note of the signal levels on the original Netgear modem - honestly did no diagnostics on the modem as felt it was a signal issue and called out Xfinity tech who 'resolved' the issue by replacing the modem (which indeed confirmed it WAS a modem issue - and the replacement - although only been on for 24 hrs at this point - also seems to be perfect) Incidentally even with the -7db splitter (which was in place during the Xfinity service call) the Xfinity tech deemed the signal level at the modem to be excellent. 

So my main question is 

Are those Upstream power levels in my new modem in acceptable range? I'm getting perfect performance comparible with my Xfinity Modem (it seems like with 3.5 splitter now, 7 before, those numbers would likely have been another 3.5dbmV higher than currently reporting, on my old configuration?) 

And generally, does the Upstream Issue outlined here manifest itself most visibly in download connection speed, not only upload? 

I guess time will tell on this replacement, but acknowledge I have undoubtedly improved the connection with only a 3.5 db split attenuation vs the 7 it had before.