Community Forum

Downstream issues

Highlighted
Frequent Visitor

Downstream issues

I recently switched plans (from 175Mbps to 600Mbps) and then a couple of weeks later switched modems from Motorola SB6121 (4x4) Motorola MB7621 (24x8). Since the modem switch, I've had all sorts of trouble, most pragmatically extremely fluctuating download speeds (between 1 and 90Mbps, which is slower than the 135Mbps that I used to get with the older modem), along with short disconnections throughout the day.
Looking into this more, the downstream channels aren't bonding, many of the channels are not locking, power levels are out of spec and some channels' SNR are too low. I also have hundreds of thousands/millions of uncorrected errors. There's also a wide range on the power and SNR levels.
Upstream looks fine, if a little on the higher end on the power levels. The upstream connectivity is quite steady and locked right around 17Mbps regularly, no matter what the downstream is like.

 

I've read through the long and very helpful Internet Troubleshooting Tips thread along with https://pickmymodem.com/how-to-fix-your-docsis-3-0-3-1-signal-issues and https://pickmymodem.com/signal-levels-docsis-3-03-1-cable-modem and https://www.motorolacable.com/documents/CableConnection.pdf

 

I also connected the modem directly to the cable outside my house (to the grounded connector) and that did not help much. I basically have a home run from there to the modem's usual place inside, with no splitters at all, just a couple of 1:1 connectors and the wallplate connector.


I've included numbers below of what it looked like when connected directly outside. Though the power levels are above -15dBmV, when inside they drop to between -15 and -17. This is after about 7 minutes of uptime, note the large number of uncorrected errors, some of which are more than the corrected ones. Usually channels 19-21 are not locked, but sometimes others are not locked too.

(You may need to scroll right to see all the columns)

 

Startup Step Status Comment
 

 



  
   Acquire Downstream Channel 543000000 Hz Locked
 

 


  
   Upstream Connection OK Operational
 

 


  
   Boot State OK Operational
 

 



  
   Configuration File OK d11_m_mb7621_extremeproplus_c01.cm
 

 


  
   Security Enabled BPI+
 

 


  

 

Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected Uncorrected/Corrected
1 Locked QAM256 21 615 -10.9 40.8 0 0  
2 Locked QAM256 2 489 -13.1 0 4703 23237 494%
3 Locked QAM256 3 495 -13.1 38.9 0 0  
4 Locked QAM256 4 507 -13.3 34.7 0 0  
5 Locked QAM256 5 513 -13.3 38.4 0 0  
6 Locked QAM256 6 519 -13.6 29.9 1654688 107419 6%
7 Locked QAM256 7 525 -13.4 0 0 0  
8 Locked QAM256 8 531 -13.1 0 0 0  
9 Locked QAM256 9 543 -12.7 31.8 357319 21259 6%
10 Locked QAM256 10 549 -12.9 39.2 0 0  
11 Locked QAM256 11 555 -12.4 30.8 29 0 0%
12 Locked QAM256 12 561 -12.2 38.5 0 0  
13 Locked QAM256 13 567 -12.1 0 79116 179177 226%
14 Locked QAM256 14 573 -11.6 0 156451 720202 460%
15 Locked QAM256 15 579 -12 33.3 14933 104 1%
16 Locked QAM256 16 585 -11.5 36.4 0 0  
17 Locked QAM256 17 591 -11.6 36.7 0 0  
18 Locked QAM256 18 597 -11.2 38.5 0 0  
19 Not Locked Unknown 0 603 0 0 0 0  
20 Not Locked Unknown 0 609 0 0 2240159 478860 21%
21 Not Locked Unknown 0 483 0 0 0 0  
22 Locked QAM256 22 621 -11.3 40.3 0 0  
23 Locked QAM256 23 627 -10.6 40.9 0 0  
24 Locked QAM256 24 633 -10.7 41.9 0 0  
                   
        Min -13.6 29.9      
        Max -10.7 41.9      
        Range 2.9 12      
                   
        Average -12.2 36.9      

 

  Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked ATDMA 2 5120 32.4 47
2 Locked ATDMA 1 5120 38.8 48.1
3 Locked ATDMA 3 5120 26 47.2
4 Locked ATDMA 4 5120 19.6 45.8
5 Not Locked Unknown 0 0 0 0
6 Not Locked Unknown 0 0 0 0
7 Not Locked Unknown 0 0 0 0
8 Not Locked Unknown 0 0 0 0

 

I should mention that on the Comcast Status Centre, it says that it can't connect to my modem, although it's able to successfully do a remote restart, though this doesn't help.

We're having trouble finding a signal

Make sure your device is connected to a power source. If you're still experiencing issues, try restarting your device.

 

I've power cycled the modem numerous times and have talked to Comcast support on chat several times, who were not able to make any progress.

I'm thinking that at this point, I need to schedule a technician to come and take a look at the external line - is that right, and if so, what's the best way to accomplish that?

Thank you!

 

 

Highlighted
Diamond Problem Solver

Re: Downstream issues

There’s no easy way to put it but your downstream levels are garbage. . Remember, this modem is accessing channels, the old modem didn’t. If it’s bad at the ground block, more than likely a bad drop but because you have service, because of the pandemic they may or may not run a tech for it. I’ll escalate it up to an Official Employee.

I am a Retired Official Comcast Employee
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark a post as the Best Answer!
Highlighted
Frequent Visitor

Re: Downstream issues

Thank you Andrew, for the confirmation! It's not just me then 🙂
Yeah, I was also thinking that the new modem is tring to coordinate 6x as much as the old one.
Thank you for escalating! I guess at this point, I should just sit tight and wait for the escalation process to run its course, right? Given that this repros entirely outside the house, I'm hopeful that they would be able to look at it without having to come inside.
Have a great weekend and take care,
Dennis

Highlighted
Official Employee

Re: Downstream issues

Hello akselk, I'd be happy to help you with your signal issues. I'll need to run some tests and look at your signal levels from my end to determine if a on site tech is needed. To get the ball rolling on this please send me a private message with your full name by clicking on my name (ComcastAmir) and then click "Send a message".


I am an Official Comcast Employee.
Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
Frequent Visitor

Re: Downstream issues

Thanks Amir! Sent you a message 🙂

Dennis

Highlighted
Official Employee

Re: Downstream issues

Thank you for this information Dennis, and thank you for being a valued customer with us since 2003. We appreciate your loyalty and I hope that you continue to choose us as your service provider for many years to come. After looking into this I see that there's two modems still listed on the system, could you please confirm your MAC address with me here? 


I am an Official Comcast Employee.
Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
Frequent Visitor

Re: Downstream issues

Sure thing - 

Old 4x4 modem: Motorola SB6121 (A4:7A:A4:78:D8:FB)

New 24x8 modem: Motorola MB7621 (00:40:36:65:83:33)

Let me know if there's any other info I could provide!

Dennis

Highlighted
Frequent Visitor

Re: Downstream issues

Hi Amir, just wanted to check if you had had a chance to check into signal levels on your end, and also if there was anything else I could provide or you'd like me to try from here.

Thanks so much for looking into this!

Dennis

Highlighted
Frequent Visitor

Re: Downstream issues

Hi,

Just wanted to check on this -- I haven't heard back since my last message, so I wanted to make sure everything was on track to get this figured out 🙂

Thanks!

Dennis

Highlighted
Frequent Visitor

Advice on scheduling technician

I've had problematic connectivity and downstream speed issues for about a month and have diagnosed it to be a problem outside of my house. I have a forum post about it here: https://forums.xfinity.com/t5/Your-Home-Network/Downstream-issues/m-p/3330119

 

I did a bunch of troubleshooting and CCAndrew confirmed my findings too. He escalated to Comcast and a Comcast employee got in touch initially, but I haven't been able to hear anything back since the initial contact.

 

I'm looking for some advice on if there's a way to move this forward, or how to schedule a technician to take a look at the node or the drop. They wouldn't need to enter my home at all, since the issue is entirely reproducible outside at the ground block.

 

Thanks!

Highlighted
Expert

Re: Advice on scheduling technician

I'm going to attempt to re-escalate this issue. Good luck !



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
Official Employee

Re: Advice on scheduling technician

Hello akselk. Thanks for reaching out for help here on our Forum. Apologies your internet issues continue. We thank you for your patience during these difficult times. In many cases, our process to escalate any line or node / plant issues must come from an in-home facing technician's referral. As you may already know, due to Coronavirus, our technicians are limited. I can assist with further troubleshooting, to determine what more can be done for you. Please send me a private message and include your full name so I can assist you. 


I am an Official Comcast Employee.
Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
Frequent Visitor

Re: Advice on scheduling technician

Thank you @EG !

Highlighted
Frequent Visitor

Re: Advice on scheduling technician

Thank you @ComcastJoeTru , will do!

Highlighted
Expert

Re: Advice on scheduling technician

Quite welcome ! Good luck with it !



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!