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Re: Low Upstream Power Level

crollman
Frequent Visitor

Re: Low Upstream Power Level

I have a similar complaint.  My Arris T25 reports upstream power in the 40dBmV ballpark.

When I talked to Xfinity tech support, they ran diagnostics on my connection with them.  The diagnostics showed no problem, with 45dBmV upstream power at their end.  I believe this defies physical laws like conservation of energy.   The signal should be lower at the receiving end (Xfinity) than at my end due to cable losses and also the 3:1 splitter at my end.

 

The implication is that either Xfinity or Arris is incorrectly measuring upstream power level.  Given that my Arris T25 is relatively new, my bet is that my modem has a bug.

CCAndrew
Diamond Problem Solver

Re: Low Upstream Power Level

@crollman , you know there’s more than 1 upstream channel. Is it possible you’re looking at one and they’re referring to a different one. If you’re not having issues, what’s the worry? They read the information that your modem gives, there’s not a separate set of numbers anywhere

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EG
Expert

Re: Low Upstream Power Level

FWIW, the upstream TX / transmit power is read at the modem level, and the upstream RX / receive power is read at the CMTS level. They are indeed two separate and distinct readings.



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crollman
Frequent Visitor

Re: Low Upstream Power Level

So you’re saying that the power level told to me by the comcast tech support person is not the power received from my modem?  That would certainly explain the discrepancy of 5dB.   

 

Still, I’m stuck between a rock and a hard place.  Arris says my upstream power is out of range and that comcast should fix it.  Yet comcast says the signals from my modem are all in range.  My problem is that Arris won’t help me debug my modem crashes further until the signal strengths are within their norms.

 

This is a classic case of finger pointing, to the detriment of the customer.

crollman
Frequent Visitor

Re: Low Upstream Power Level

So my Arris T25 modem crashed again last night.  I woke up this morning to no internet.  I was able to reset the modem using the xfinity website, so it was at least connected and listening.  After reset, I now have internet access.

 

My prior Arris SB6141 very very rarely caused me any grief, so I view the crashes I've experienced with the T25 as abnormal.

 

Arris says that, until/unless my upstream power level exceeds 45 dBmV (it's currently 40.00 to 41.25 dBmV), there is nothing they will do.  They make clear they think this is an ISP problem.

 

Xfinity can find nothing wrong with my service, and basically shrugs me off.

 

Somebody here is going to lose my business.

EG
Expert

Re: Low Upstream Power Level

FWIW, Arris is wrong ! They are passing the buck with that statement lately ! Only the Comcast plant / engineering specs matter;

 

Specification      Min             Max
Downstream Power Level    
Cable Modems -10dBmV +10dBmV
Gateways and EMTAs -7dBmV +7dBmV
Downstream Signal to Noise Ratio 35dB -
Upstream Power Level +35dBmV +50dBmV
Upstream Signal to Noise Ratio 31dB -
Upstream Receive Power -2dBmV

+2dBmV

 

Something else is going on. You didn't post the downstream power and the SNR stats.



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crollman
Frequent Visitor

Re: Low Upstream Power Level

I agree something else is going on.  The problem is that for me to get help from Arris, the upstream power needs to be within their specs before they will dig deeper.  

 

I hate it when I get caught in the middle between two vendors whose tech support people are mostly interested in avoiding having to dig deeply into a problem. 

 

Since Xfinity recommends the Arris T25 modem, what I'd really hope would happen is that Arris and Xfinity would talk to each other and agree jointly on what upstream power level reported by the T25 is ok.  This would likely solve more than just my immediate problem since others have bumped into the same roadblock when engaging Arris customer support.

 

Arris is happy with my downstream power and SNR.  My current numbers are....

 

Downstream powers range from 0.50 dBmV at the higher frequencies to 5.20 dBmV at the lower frequencies.  For reference, Arris acceptable range is -15 dBmV to +15 dBmV.

 

SNR ranges from 37.64 dB to 38.98 dB with 256QAM modulation.  For reference, Arris wants 30 dB or greater for 256QAM and downstream power of -6 dBmV or higher.

 

 

crollman
Frequent Visitor

Re: Low Upstream Power Level

It just dawned on me this morning that, based on your table, the Arris T25 acceptable upstream power level can exceed the Xfinity spec.  Arris quotes maximum upstream powers from 51 to 61 dBmV depending on number of channels and symbol rate.  The Xfinity spec limits the maximum to 50 dBmV per your info.

 

Xfinity and Arris really need to mutually line up their ducks.  ...Or Xfinity needs to stop recommending the Arris modem.

EG
Expert

Re: Low Upstream Power Level

 The upstream power being above 51 dB causes random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of the multiple bonded channels on the Comcast system.




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jgordon
Regular Visitor

Re: Low Upstream Power Level

I have exactlly the same issue and low upstream power levels with Arris T25.  Did you ever get it straightened out?    I have to reset modem about twice a week as it drops off in the early morning hours.   Frustrated!

crollman
Frequent Visitor

Re: Low Upstream Power Level

It's clearly the Arris T25 modem. 

At a recommendation from Comcast, I rented an xfinity modem and swapped it out with my Arris T25.  The Xfinity modem has not crashed in over a month.


Arris is willing to swap out the T25, but wants me to first reinstall it and let them revisit the power levels it reports after the xfinity modem has worked so well.  They want to make sure that Comcast didn't fix something (which I'm pretty sure hasn't happened).  I started to do this and my wife squawked because she needed to use the internet.  I haven't yet gotten back to it.

crollman
Frequent Visitor

Re: Low Upstream Power Level

I should add that I'm doubtful that swapping out the Arris T25 will change anything.  This smells like a design problem to me, based on others having similar complaints.

jgordon
Regular Visitor

Re: Low Upstream Power Level

I had Arris swap out the T25 once already and am getting the same results.  i had no issues with my older Arris Modem but not 3.1 and could not handle the higher speeds.  

 

I would seem to agree that the T25 is the issue.  What did Xfinity suggest for a Modem as a replacement?

crollman
Frequent Visitor

Re: Low Upstream Power Level

Xfinity has an 'xFi Advanced Gateway' that they push.  It's a combination modem and wifi capable router.  I'm just using it as a modem because I didn't want to mess with my faithful Asus router, nor did I want to host an xfinity hot spot.

https://www.xfinity.com/learn/internet-service/modems-and-routers


The T25 is on Xfinity's approved list.  Makes me think they didn't test it much prior to approving it.

I had the same experience as you: years of reliable service from my prior Arris modem.  I stuck with Arris because I had previously had good experience with them.

cindywade
Frequent Visitor

Re: Low Upstream Power Level

Of ocurse the xfinity rental doesn't crash, people wouldnt pay $14 month for a crash prone modem. I have up stream signals around 41.  My T25 was fine for about 6 months. For the past 2 months is disconnects once a week. I'm sure it has to do with Comcast but don't understand the error logs. I will save a few more weeks and then see if someone can tell me what they mean.

 

I need this to work while i'm away in a few weeks for security cameras etc. My plan is to get digital outlet timers and have then turn off the modem twice at week late at night and then back on after 10 minutes. I'll do the router too, but have it restart 10 minutes after the modem.

 

I can't have it be doing this every week becasue my hsband nneeds it for work and it tends to go out in the morning. I'm hoping if I power cycle it twice a week that will help.  Maybe while i'm away I should set it do it every night, in case it happens on the ay after I power cycle it. That way I  will only lose one day. Sure wish I could power cycle it remotely, but you need internet to do that!!

mike010
New Poster

Re: Low Upstream Power Level

I've had a similar experience to others in the thread. Signed up for Xfinity 6 months and purchased the Arris T25, which I validated is supported by Xfinity. I've had periodic disconnections from the internet which are incredibly disruptive. My T25 logs shows upstream power levels of ~33 dBmV. Arris support told me it's not in their acceptable range (minimum +45 dBmV). They pointed me to Comcast support. Comcast support was useless and pointed me to Arris support.

 

I wound up renting the XB6 through Comcast because they have a monopoly in my neighborhood and I have no other choice. It's worth $14/month to not have to speak to Comcast support ever again, although I know I'm being extorted.  

 

Comcast and Arris need to be in alignment in acceptable ranges for upstream/downstream power levels if they are going to claim the T25 is supported.