Question Cablemodem - intermittent unexplained reboots

Nov 15, 2019
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This has been an ongoing issue for quite some time at the business I work at: the cablemodem reboots intermittently (on average once a day) -- taking around 4 minutes to completely reboot. During that time, internet is down (of course) along with the phone lines attached to that cablemodem.

BACKGROUND:

The building we're in has a total of 4 businesses located inside of it (4 suites) -- all with internet access. All with their own droplines. None have this problem -- I checked by looking at their cablemodem status page and checking the cablemodem uptime.

When the cablemodem reboots, there is no error log entry for it around that time -- nothing at all unusual. No T3 or T4 timeouts. Correctables and Uncorrectables are totally normal. I can tell when the cablemodem reboots in three ways:
  1. experiencing it (although i'm usually not onsite when it happens, but sometimes I am)
  2. looking at the uptime shown in the cablemodem status webpage
  3. looking at the packetcable mta events for when the phone line, for example:
11/13/2019 3:08​
16​
MTA TFTP: Successful​
11/13/2019 3:08​
26​
MTA PROV: Successful!​
11/13/2019 3:08​
3​
Voice Line State Change, Line Number = 1, Prev State = OOS, New State = IS​


Our ISP (optimum) owns all the networking hardware before (and including) the router: drop line (obviously) -> 2-way splitter (indoors) -> two cablemodems (to support a total of 5 phone lines) -> router. After that, we own the hardware, but there's nothing unusual going on (a switch, cat6 cabling, desktop PCs).

I only have access to the logs/status page of one of the cablemodems -- the one with 1 phone line and internet. The other just has 4 phone lines and is not attached to the router -- which is why I don't have access to the logs -- it doesn't have an IP address on the network. All I can say for certain is that the other cablemodem doesn't reboot at the same time.

Going to 192.168.100.1 gives me the status page for the cablemodem that handles internet access for the building. Currently, it's an Arris TM1602AP2 -- but this is the 14th time (literally) that the cablemodem has been replaced by optimum techs for this issue. Other things that they tried:
a) replacing all hardware from the router to the dropline (including the drop line and the router itself)
b) reprovisioning the other cablemodem (that usually just handles 4 phone lines) to handle the internet as well
c) dropping our static IP address (it's not critical for us to have one, so we figured why not try that since the other businesses in the same building don't have one)
d) dropping bandwidth from around 200mbps to 100mbps because that's what the other businesses have.
e) 6db attenuator (aka a pad)


Now, I'm not a cable tech. I'm a programmer, and (of course) I end up doing a lot of IT work. While there may have also been problems with that hardware (router to dropline) in the past (there was a serious packet loss issue that was resolved with replacing the dropline), it seems to be a problem related to the balancing of the power levels -- our business in the building (there are 3 other business and they do not have this problem) and all of them have MUCH longer line runs than us.

Our business has the shortest run. All the other businesses have an additional 150 to 200 feet of cable before their cablemodem than us. It seems like the powerlevels are balanced in general for the whole building -- not for us, and we're getting screwed by that.

Powerlevels (averages, cold weather -- it's much worse the colder it gets):

Right now:
Without an attenuator / splitter:
Downstream: +18 dbmv (waayyy too high)
Upstream: 42 dbmv (great)

We do absolutely need the 2 way splitter though, so:

With splitter (but no attenuator):
Downstream: +15 dbmv (too high)
Upstream: 45 dbmv (great)

With 6db attenuator (what I'm using now and crossing my fingers hoping for the best):
Downstream: +9 dbmv (on the high side)
Upstream: 51 dbmv (starting to get high)

Using an attenuator, the above is the best we can do.



MY REAL QUESTION:

Would removing the attenuator, and instead add an extra 150 feet of cable to the dropline result in better downstream/upstream power level balance? Because that's really the ONLY difference between our suite in the building and the 3 other businesses there (we have a much shorter run than any of them).

THEIR powerlevels right now (NO attenuator, one 2-way splitter):
Downstream: +9 dbmv
Upstream: 42 dbmv

OUR powerlevels right now (NO attenuator, one 2-way splitter):
Downstream: +15 dbmv (too high)
Upstream: 45 dbmv (great)

The only difference at this point is their drop line length (+150 - 200 ft)!

EDIT 1: Changing ISPs isn't an option -- Verizon FIOS isn't offered in our area.
EDIT 2: Optimum wouldn't just give us an extra 150 feet of cable, but I could just buy it myself.
EDIT 3: I don't know what's going on at the dropline tap at all, and neither does optimum apparently. All businesses in our building have their own dropline running from the pole, though, so I'd imagine there's no tap... but there might be, but then the tap would have to be at the pole itself.
 
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USAFRet

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Mar 16, 2013
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If the ISP 'owns' the cable modem, and that is the component that is failing, make them fix it.
Either repair or replace.

At the very least, they can come out and troubleshoot to indicate where the actual problem is,if not the cable modem.
 

Ralston18

Titan
Moderator
Has anyone checked the outlet/electrical circuit/ power supply serving the cable modem(s)?

What else is plugged into that outlet and circuit?

Maybe borrow a UPS and connect the cable modem to the UPS for a while.
 

rcfant89

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Oct 6, 2011
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You've been through 14 modems!?! Sounds like a power issue with your wall plug my dude. I would start by picking up a UPS, your modem (and router/switch) should be on a UPS anyway, esp if it's for business in an office.

I might also plug a desktop computer into the same outlet and let it run, set it to never go to sleep or shutdown. If you come in the next day and it's off, power issue. Maybe try that over the weekend.

If that is confirmed I would def. get an electrician to take a look at the run. Maybe a rat gnawed through it or it's improperly done, could be a fire hazard. Good luck.
 
Nov 15, 2019
4
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10
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If the ISP 'owns' the cable modem, and that is the component that is failing, make them fix it.
Either repair or replace.

At the very least, they can come out and troubleshoot to indicate where the actual problem is,if not the cable modem.
If they were competent enough to solve the problem, then it would have already been solved by now.

But, you're right, they're responsible for their own hardware. However, I've become responsible for getting the internet working with some measure of reliability by the owner of the company I work for.
 
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Nov 15, 2019
4
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Has anyone checked the outlet/electrical circuit/ power supply serving the cable modem(s)?

What else is plugged into that outlet and circuit?

Maybe borrow a UPS and connect the cable modem to the UPS for a while.
There's nothing wrong with the power outlet.

The router and both cablemodems are on the same outlet.

If there was a power issue, then the other cablemodem would be affected. Also the router. They are not affected.

Also, some of the cablemodems we've had were business class -- they had their own battery. They still rebooted (whichever one was providing internet) -- the other devices don't reboot.
 
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Nov 15, 2019
4
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You've been through 14 modems!?! Sounds like a power issue with your wall plug my dude. I would start by picking up a UPS, your modem (and router/switch) should be on a UPS anyway, esp if it's for business in an office.

I might also plug a desktop computer into the same outlet and let it run, set it to never go to sleep or shutdown. If you come in the next day and it's off, power issue. Maybe try that over the weekend.

If that is confirmed I would def. get an electrician to take a look at the run. Maybe a rat gnawed through it or it's improperly done, could be a fire hazard. Good luck.
There was nothing wrong with those other cablemodems -- it's just that most optimum techs are incompetent. I imagine the same is true for Cox and Verizon, so I have nothing personal against Optimum. They show up, have no idea, and just replace the cablemodem even though I tell them it was just replaced because then they can do that and quickly leave -- another ticket marked off as completed.

Some of the cablemodems we've had on that outlet were business class modems that had their own internal battery -- they would still reboot.

Also, all devices plugged into the same outlet (other cablemodem, and the router) would be rebooting if the outlet lost power -- they do not reboot. Or, at least, they're not rebooting at the same times -- there is no log in the router's status page to check uptime, but we never noticed the router going down.

I've physically witnessed the primary internet cablemodem rebooting when nothing else rebooted.

The problem is kinda obvious (signal powerlevel balance) -- I'm not really looking for troubleshooting ideas -- I've been working with optimum techs to resolve this issue for over a year.

I really just need to know if I can expect to have lower upstream signal powerlevels when using an additional 150' of cable as opposed to using a 6db attenuator to lower the downstream signal powerlevels.

I personally KNOW that both 150' of additional cable line and a 6db attenuator will lower downstream powerlevels by 6db/mv. I need to know whether the upstream signal will be affected differently or the same. They each would lower downstream signal strength a different way, so it's possible I'd get better upstream powerlevels with the additional cable in place -- I just don't know for sure.

I'm looking for someone with telecom cable experience to answer. If I don't get an answer, fine, I'll just end up buying the equipment (150' coax cable + male connector) anyways and seeing if it's an improvement or not.
 
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Ralston18

Titan
Moderator
Question:

"Also, all devices plugged into the same outlet (other cablemodem, and the router) would be rebooting if the outlet lost power -- they do not reboot."

Does that mean there is some sort of outlet strip being used with one plug into the wall outlet and then the other cablemodems and router plugged into different outlets on the power strip?

Also:

You should be able to determine the attenuation of downstream power levels by using a look up table such as the following example:

https://www.fmsystems-inc.com/attenuation-standard-coaxial-cable/

There are also a number of online calculators available that should assist in working out the downstream powerlevels.

Sketch out the current and proposed cable paths. Plug in the attenuation values applicable to your environment.

Lastly:

The following link provides some insight that may prove useful to you.

As you noted in your original post, the attenuation is worse in cold weather.

https://broadbandlibrary.com/long-loop-alc/
 
It may depend on the cable modem but generally if the box just reboots as compared to power cycle it retains the log. You should see errors in the log. Generally if you get lost sync it will cause the device to go though its retraining function.

The ISP should be able to fix signal issue that cause this. You might be able to find other attenuators that only degrade downstream frequencies Most the cable systems I have seen the upstream frequencies are much lower than downstream ones. .
 

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