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Degraded download speed, downsteam bonded channel not locked, large uncorrectables

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Regular Visitor

Degraded download speed, downsteam bonded channel not locked, large uncorrectables

Hello and thank you in advance for any help. I'm a 10+ year Comcast customer; physical exterior wiring untouched since initial customer onboarding. I'm on an up-to 300Mbps plan and until ~2 months ago was receiving consistently >150Mbs over WiFi, which was totally acceptable. No known changes have occurred on my property that would have detrimentally impacted Internet performance. I live at the end of the street = no homes downline of me. Currently, I'm receiving ~35Mpbs maximum wired directly into the cable modem (Arris SB6190). I've activated and provisioned an older second cable modem and the same hardwared download speed performance is observed: ~35Mpbs maximum. On both cable modems tested, there are consistently 3-4 downstream channels either showing Not Locked or some other form of distress, and usually one channel with an overwhelmingly large number of Uncorrectable errors. These 3-4 channels are always grouped together, but do change when the modem is powercycled I've included both my SB6190's Status and Event Log at the bottom.

 

Objective: determine whether my two cable modems are both defective and require replacement or whether I need a Comcast tech to come out and rehab my wiring/installation. I'd like to remove WiFi entirely from the equation and just focus on speed as measured while hardwired into the cable modem. 

 

As a 10+ year Comcast customer, I am familiar with Xfinity quirks: weekly (or more frequent) cable modem power cycling, call in to have cable modem reprovisioned, etc. I've tried all prior tactics to get my download speeds back up to an approximation of what I'm paying for, to no avail.

 

I've chatted with Comcast support twice, we do the same standard reboot process, the agent confirms she can proceed no further, and then I'm supposed to receive a call from Advanced Support, which is never received.

 

Whether coincident or causal remains unknown: my ex-AT&T customer neighbor two houses up-line became a Comcast customer, enjoys glorious >600Mbps over WiFi, having a model experience. This customer's Xfinity activation approximately aligns with my observed download speed performance decline.

 

My SB6190's Status - currently Channels 10, 11, and 12 show distress - the specific channels in distress change when I powercycle, but 3-4 adjacent channels consistently show problems:

Downstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectedUncorrectables
1Locked256QAM21555.00 MHz-1.80 dBmV37.36 dB00
2Locked256QAM13495.00 MHz-1.10 dBmV37.64 dB00
3Locked256QAM14507.00 MHz-1.00 dBmV37.64 dB00
4Locked256QAM15513.00 MHz-1.30 dBmV37.36 dB110
5Locked256QAM16519.00 MHz-1.30 dBmV36.61 dB130
6Locked256QAM17525.00 MHz-1.20 dBmV36.61 dB120
7Locked256QAM18531.00 MHz-1.40 dBmV34.48 dB50
8Locked256QAM19537.00 MHz-1.30 dBmV35.60 dB200
9Locked256QAM20543.00 MHz-1.40 dBmV34.93 dB20
10Locked256QAM22561.00 MHz-1.70 dBmV31.69 dB173161613
11Not Locked----23567.00 MHz----------------
12Locked256QAM24573.00 MHz-1.70 dBmV27.64 dB194223275612
13Locked256QAM25579.00 MHz-1.90 dBmV34.93 dB990
14Locked256QAM26585.00 MHz-2.10 dBmV37.36 dB00
15Locked256QAM27591.00 MHz-1.90 dBmV37.36 dB00
16Locked256QAM28597.00 MHz-1.90 dBmV37.36 dB00
17Locked256QAM29603.00 MHz-1.80 dBmV37.64 dB00
18Locked256QAM30609.00 MHz-1.90 dBmV37.36 dB00
19Locked256QAM31615.00 MHz-2.20 dBmV37.36 dB00
20Locked256QAM32621.00 MHz-2.10 dBmV37.36 dB00
21Locked256QAM33627.00 MHz-2.30 dBmV36.61 dB20
22Locked256QAM34633.00 MHz-2.30 dBmV37.36 dB00
23Locked256QAM35639.00 MHz-2.20 dBmV36.61 dB00
24Locked256QAM36645.00 MHz-2.40 dBmV36.61 dB00
25Locked256QAM37651.00 MHz-2.60 dBmV36.90 dB00
26Locked256QAM38657.00 MHz-2.30 dBmV36.90 dB00
27Locked256QAM39663.00 MHz-2.60 dBmV36.60 dB00
28Locked256QAM40669.00 MHz-2.60 dBmV36.60 dB00
29Locked256QAM41675.00 MHz-2.20 dBmV36.90 dB00
30Locked256QAM42681.00 MHz-2.50 dBmV36.60 dB00
31Locked256QAM43687.00 MHz-2.40 dBmV36.60 dB00
32Locked256QAM44693.00 MHz-2.30 dBmV36.40 dB60

 
Upstream Bonded Channels
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA65120 kSym/s29.20 MHz52.50 dBmV
2LockedATDMA85120 kSym/s16.40 MHz54.00 dBmV
3LockedATDMA75120 kSym/s22.80 MHz52.50 dBmV
4LockedATDMA55120 kSym/s35.60 MHz52.50 dBmV


 

Current System Time: Mon Sep 21 09:17:17 2020

 

The Event Log is an infinite stream of this:

Event Log

The table below contains the log of events that the SB6190 has detected. This log can be important to the service provider to help diagnose and correct problems, if any should occur.

Time Priority Description
Mon Sep 21 09:17:06 20205Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:08 20205RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:14 20205Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:14 20205RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:26 20205Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:26 20205RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:34 20205Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:34 20205RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:36 20205Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;
Mon Sep 21 09:17:37 20205RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0;

 

Thank you in advance for any help/guidance offered.

Highlighted
Gold Problem Solver

Re: Degraded download speed, downsteam bonded channel not locked, large uncorrectables

Besides the several downstream channels you mentioned, all four upstream channels are out of spec/too high.

If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you can't find the problem or you'd rather have Comcast take care of it, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. If they can't fix the problem remotely (unlikely), insist they send a tech out to identify the cause and correct it.

If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have their Service Protection Plan (https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device, or anything outside your home, you shouldn't be charged.

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Regular Visitor

Re: Degraded download speed, downsteam bonded channel not locked, large uncorrectables

Thank you very much @BruceW ! I appreciate your time and assistance - will update on resolution.

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Regular Visitor

Re: Degraded download speed, downsteam bonded channel not locked, large uncorrectables

Updating and closing out this thread: on @BruceW 's recommendation, I requested Comcast send a technician to review overall installation status. Tech arrived yesterday afternoon, assessed all exterior lines/connectors, and tested signal health at each junction.

 

Observations/actions:

  • Cables themselves in acceptable shape from the pole to house
  • Replaced all exterior connectors, some with observed corrosion
  • Removed signal booster/power supply which had been previously installed; tech advised this is unneeded for my configuration and may contribute to degraded download speed performance
  • Tested signal at all exterior connection points:
    • Clean signal from pole to house
    • Clean signal from main exterior junction to attic entry
    • Observed signal noise over in-attic line, which feeds the cable modem

Cable from exterior attic entry to the cable modem is perhaps 130', with at least one known splitter. To address in-attic signal noise would require in-attic inspection, splitter replacement, possible cable replacement, etc. We decided not to do that at this time.

 

Upon fitting the exterior cabling with modern-style connectors and removing the signal booster (which was itself determined to have little benefit/detriment in our testing), now receiving strong performance inside the house at the cable modem.

 

Outcome: All errors originally listed above and four downstream channels in distress have been resolved, all 32 downstream channels are now Locked, 0 Uncorrectable errors on all downstream channels, and download and upload speeds are in line with or exceed my plan (>300Mbps down, >20Mbps up). All four upstream bonded channels are at 48.25 dBmV.

 

The technician advised/reminded me that the signal noise in the attic cabling remains, which may contribute to variable download speeds. We'll address this subsequently if it presents as an issue.

 

Many thanks!

Highlighted
Gold Problem Solver

Re: Degraded download speed, downsteam bonded channel not locked, large uncorrectables


@JB27 wrote: ... All four upstream bonded channels are at 48.25 dBmV. ...

That's awfully close to the upper limit, but should be OK if it's stable. Here's hoping it holds for you!

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Official Employee

Re: Degraded download speed, downsteam bonded channel not locked, large uncorrectables

Thank you for reporting back! Take care. 


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