CM1150V modem frequent and long reconnects more recently - upstream channel issue.

Hi,

I found this forum somewhat helpful and and going to post my experience troubleshooting a problem with the CM1150V.  I have not found root cause, but seem to have resolved it for now swapping out another brand of modem.  I'm wondering if others have similar problems.

About 9 months ago, I updgraded service to 600 Mbit/s finity service, bought a docsis 3.1 CM1150V recommended from Xfinity.   Worked great, no issues.  Come mid-December, my Sonos streaming radio starts dropping out, restarting, sometimes just stopping altogether for 20 minutes.  Concurrently, started to have other connectivity issues on video conference calls, modem getting stuck and needing reboot, going offline for minutes at a time.  Sometimes, no service for 20 minutes.  At first, I thought they were performiing line maintainance.  Except it continued and the dropouts got worse.  My morning radio streaming couldn't stay online past 5 minutes at a time, the Roku streaming video (directly wired) actually was almost fine for the most part, except for a few minor annoying short drops every evening, it's buffers seem to handle better than the Sonos radio streaming.

I have the Orbi's RBR50's for Wifi, it does a speed test, no issues - plenty of downstream speed.  I did notice upstream was getting a little faster over the months, from about 9 mbit/s to about 14 ms/sec now, interestlingly, my download speeds seem to degrade some from 450 Mb/sec earlier in December to about 300 Mb/sec now (Dec-22).  I'm familiar with the upstream power issue from a few years ago, troubleshooting a bad coax - and the colder temperatures seem to precipitate these problems.  While all my down/upstream power readings were well in spec, I did notice numerous T3 ranging requests were logged - one every few minutes, I then went on a campaign to simplify the connectivity and try several other cable paths in the house, inlcuding a direct hookup to outside box.  It was a waste of time - the modem would spend a random time period to reconnect - sometimes 2 minutes, sometimes 20 minutes - no matter how I hooked it up.  I did lots of online searching to see what the problem might be to no avail.  I do believe it has something to do witht his upstream channels, even though I have no big speed problems, plenty of bandwidth overall - my problems are the modem going offline for anywhere from 2 to 20 minutes at a time and frequently. 

I did find an odd reading on the upstream channels, only one upstream channel seemed to lock and it was the lowest frequency, 17.3 MHz at 44.5 dBmV power (power seems inline) and showed "partial service" status.    I reasoned it might have something to do with my problem, I saw so many other postings here with multiple channels locked, and many of my T3 errors would refer to a second channel that seemed to not show being locked.

I wasn't clear on the root cause, it could be the modem HW going bad (I've had a few go bad in the last 20 years) or could be a firmware update - my modem was running v4.02.02 - or combination of both, or the IS provider did something, or perhaps a noisy neighbor line, or some combination.   It's hard to diagnose since telecommnications are so interdependent, but I do know the long and often variable 20 minutes to reconnect wasn't normal and didn't seem to matter how I hooked it up with various simplified wiring.

I decided to swap out and try an Arris T25 modem, it has similar specs, but different chipsets and firmware altogether.  If this doesn't work, then I reasoned I have a good case for the IS provider to check their end.

The T25 came up quickly, good and quick self-service provisioning provided by Xfinity/Comcast (I said something nice about them :) ).  First thing I noticed is now I have multiple upstream channels, and on the highest 2 frequencies 36.7 MHz and 41.2 MHz at 42.75 dBmV and 45.75 dBmV respectively.  The T3 errors still continued at the same rate, so I wasn't sure if it made a difference at first.

After 24 hours, I've not had any offline events - clearly a signficant difference.  Upstream data rates are now over 18 Mb/sec, I think the IS has been improving this capability since it's a competitive disadvantage to fiber optic, perhaps my CM1150V might have started struggling, triggering offline events and long reconnects when they started to updgrade capability.

I'm not sure what to do with the CM1150v - it might be fine, perhaps roll back the firmware might make a difference if possible and sustainable.  HW could have degraded over time, or could have remained the same and IS started to upgrade the lines to faster speeds, sent out updated firmware, and created a problem for my modem.  I really don't know.  I thought I'd post here to see if anyone knows more definitely what's going on, aside from a faulty modem which is my default belief - either from the beginning and became a casualty over line and FM upgrades, or simply degraded over time.  I'd be willing to roll back FW and re-provision if there was an explanation to indicate a reasonable chance of prolonged success, then I could return the T25 and continue with the CM1150V.

However, connectivity these days is important to myself and wife for work, so having a spare modem of different chipset/firmware ready to go seems wise, albeit a little costly upfront.  I am aware of the troubles written of the T25 Intel chip, but so far, no issues here and these seem minor to my troubles.  I'd really rather know what's gone wrong so in the future, I can better address issues like this.

Another note:  I seem to always have trouble when it gets cold outside, I believe the upstream capabilities are the most challenging technically, and stress the modem capabilities the most.  At least that seems to correlate to my problems.  I've had overpowered upstream ampilification that results in modem overheating and resetting (a problem I had years ago on a prior modem, bad cheap in-house coax was the blame pushing upstream power to over 50 dBmV) that only happened when it got below freezing temperatures here - a result of the line resistance dropping.  Recently, similar situation, except it's not a power issue, but rather a channel spectral response change to go from barely acceptable performance to unacceptable in the frequency domain as a result of resistance drop due to colder temps, and my marginal setup and configuration is vulnerable.  I'd be curious to know if xfinity/comcast service calls uptick when the temperatures drops outside each season.

Attached are status screenshot on CM1150V and new Arris T25 screenshot below it.  Note upstream channels status in each case.  Numbers are consitent after restiing, except upstream power creeps up a bit over time (e.g. 39 dBmV to 44 dBmV ) but stays in spec.  Note each vendor may have different ways to measure the same thing, so I wouldn't get too hung up on dBmV and power level comparisons as long as they are in spec.  The upstream channels - the number and frequency -  seem to stand out.

CM1150V status screenshot 1CM1150V status screenshot 2CM1150V status screenshot 3 with Upstream "Partial Service" indicatedArris T25 status screenshot 1Arris T25 status screenshot 2 - note change in # of upstream channels and frequencies.