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Need a little help with upstream SNR and slow upload speeds

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Need a little help with upstream SNR and slow upload speeds

Hoping this is the right place to get a little help.  This past week started to experience slow upload speeds.  Called Comcast on a Tuesday, tech arrived Wednesday to diagnose.  Using a meter he diagnosed the problem to low SNR impacting upload speeds.  He also checked every connection from the pole to the modem, changing out some wires, grounding blocks, splitters and adding new all weather connectors for anything outside.  He even took my modem to the pole and verified low SNR.  Although he tried to eliminate any postnetial for noise, he said the issue was outside plant related and nothing to do with my modem - which he thouroughly tested.


He then put in a ticket to have the issue resolved by another group.  I have the job number if that matters - jb20464500.  Something was done and upload speeds returned to the normal 10-12mbps that I was experiencing for the last several years - for two hours.  Unfortunately, I have the same problem again.  Making a call to Comcast a second time was extremely frustrating, with the agent making me go through all the steps on their screens to diagnose the issue (modem reset, etc etc).  I provided the job number of the service that was supposed to have ocurred, and they said the work was done - thus its your equipment.  Bottom line - it was a fight to get someone out here again.  The problem is that they are going to do what the previous tech did - basically deja vous all over again.  


Is there a way to have Comcast fix this issue without having a truck roll given that the problem is low SNR?  Isn't this a CMTS issue and can't this be checked, as the tech did, remotely?  


Tech coming out this Saturday for the 2nd time, any help would be appreciated, thanks in advance.




For the record, I have a Dlink and Arris DOCSIS 3.0 modems, both are experiencing the same issue.


Here's a speed test from this morning...ouch  118.85 and 0.99




This page displays information on the status of the cable modem's HFC and IP network connectivity.
Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 519000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
Security Enabled BPI+

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 10 519000000 Hz -1.4 dB 41.8 dB 0 0
2 Locked QAM256 12 531000000 Hz -1.4 dB 41.3 dB 1 0
3 Locked QAM256 13 537000000 Hz -1.5 dB 41.4 dB 1 0
4 Locked QAM256 14 543000000 Hz -1.1 dB 41.3 dB 5 0
5 Locked QAM256 17 567000000 Hz -1.0 dB 41.7 dB 0 0
6 Locked QAM256 19 579000000 Hz -1.1 dB 41.9 dB 1 0
7 Locked QAM256 22 597000000 Hz -2.8 dB 41.3 dB 1 0
8 Locked QAM256 23 603000000 Hz -3.4 dB 40.9 dB 0 0

Total Correctables Total Uncorrectables
9 0

Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 70 5120 Ksym/sec 29200000 Hz 45.0 dB
2 Locked ATDMA 69 5120 Ksym/sec 35600000 Hz 45.0 dB
3 Locked ATDMA 71 5120 Ksym/sec 22800000 Hz 44.8 dB
4 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dB

CM IP Address




Re: Need a little help with upstream SNR and slow upload speeds

FWIW, the stats as read at the modem level at that moment in time were o/k but there are three additional signal stats which can't be read by the modem. They can only be read from their end by them polling the CMTS (Cable Modem Termination System) at the local headend facility.

They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.

You can call in and ask what these figures are. The Upstream Receive Power Level should fall within the range of -2dB to +2dB with 0dB being in the middle and perfect.

The Upstream SNR should be least 31dB, and the higher it is the better.

The ICFR should be no higher than 2 dB.

You could have an intermittent noise ingress issue in only the upstream channel(s) / return path only somewhere.

They will be able to see whether or not everything is in the green zone and also see a history plot for the modem.

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I am a fellow customer, volunteering my time to help other customers here in the Forums.
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Regular Visitor

Re: Need a little help with upstream SNR and slow upload speeds

Thanks for your help, will wait for the 2nd tech.  Was hoping to avoid the hassle!


Re: Need a little help with upstream SNR and slow upload speeds

FYI: They owe you a $20 credit for every tech visit after the first for the same problem.You can also get a credit for your service from the time you first reported the issue until it is resolved.

I am not an employee.
Regular Visitor

Re: Need a little help with upstream SNR and slow upload speeds

Very helpful.  As I mentioned before, I don't want to continue to go through this circle with Comcast everytime just to get a tech to fix something on their end.  Anyone reading these forums knows the challenges of dealing with their first line CSRs.  I'm reminded of groundhog day the movie, which is today...