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frequent outages and DOCSIS disconnections

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frequent outages and DOCSIS disconnections

Hello,

I have 1Gbps Xfinity and am experiencing frequent DOCSIS disconnections with 1 to 10 minute outages. Comcast has sent out several techs but unfortunately there has never been an outage while they're on site. To be clear it is not a router issue! During outages the modem reports the service provider is offline. I have already replaced my modem and experience the same behavior. My new modem (MB8600) is connected directly to the demarcation point of the property. It is not connected to any home coax or splitters so the signal integrity is optimal.

My current line of investigation is a large number of packet errors I observe on channel 32. I should note that other channels have small number of packet errors. The peak SNR is 40.9dB (channel 6) which should be sufficient.  However my modem manual recommends that all channels be within three dB of each other. Suspiciously channel 32 is 3.9dB less.

I need to figure out the large number of packet errors on channel 32. I suspect it may be a filter at the Comcast end. However, this may be a red herring because during the outages I experience packet errors on all channels.

 

I am completely out of ideas. At this point I am certain this is a complicated service provider issue.

 

It is frusterating that despite multiple technician visits Comcast has not found any problem. Because of Covid I am working from home, and frequent disconnects from video conferences is unacceptable. I unfortunately do not have any other service providers in my area.

I need help to debug the issue.

joel

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Re: frequent outages and DOCSIS disconnections

Just happened again. Here's a snippet of the modem event log:

 

11:10:01
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:04
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 4; Chan ID: 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;C
11:10:07
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 1; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:09
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:11
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 22; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:16
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 1 2 3.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:17
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:23
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 4; Chan ID: 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.
11:10:24
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0 1 2 3.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:10:35
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:11:04
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 22; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:11:32
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:11:33
Sat Jul 25 2020 Notice (6) CM-STATUS message sent. Event Type Code: 21; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;
11:11:34
Sat Jul 25 2020 Warning (5) MDD message timeout;CM-MAC=00:40:36:61:5f:f8;CMTS-MAC=00:01:5c:cd:ca:5e;CM-QOS=1.1;CM-VER=3.1;

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Expert

Re: frequent outages and DOCSIS disconnections

Does that channel 32 say OFDM or Other ? There is a known glitch with some makes / models of modem's firmware where the measuring mechanism incorrectly reads the power level, the SNR, and the bit errors for that channel. So it reads many errors when there really isn't.


Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers for us to see. 



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Re: frequent outages and DOCSIS disconnections

Interesting. Here are my up/downstream levels:

Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
1 Locked QAM256 12 453.0 -1.6 40.0 30684 1356
2 Locked QAM256 13 459.0 -1.5 40.2 107701 4605
3 Locked QAM256 14 465.0 -1.1 40.2 1138872 86210
4 Locked QAM256 15 471.0 -0.5 40.4 3601342 1456276
5 Locked QAM256 16 477.0 0.2 40.5 2192096 555089
6 Locked QAM256 17 483.0 0.7 40.7 2305996 1565077
7 Locked QAM256 18 489.0 1.1 40.7 1960844 1072255
8 Locked QAM256 19 495.0 1.0 40.7 3758112 1808840
9 Locked QAM256 20 507.0 0.0 40.5 2471341 669315
10 Locked QAM256 21 513.0 -0.9 40.2 2135008 368093
11 Locked QAM256 22 519.0 -1.7 39.9 1991251 546172
12 Locked QAM256 23 525.0 -2.4 39.6 2701827 679605
13 Locked QAM256 24 531.0 -2.6 39.5 2060333 937173
14 Locked QAM256 25 543.0 -2.1 39.5 2912824 1091201
15 Locked QAM256 26 549.0 -1.2 39.9 4755357 2012037
16 Locked QAM256 27 555.0 0.1 40.3 4986388 2439662
17 Locked QAM256 28 561.0 1.3 40.4 3174711 1617448
18 Locked QAM256 29 567.0 1.4 40.5 5047047 1345736
19 Locked QAM256 30 573.0 0.9 40.3 3970911 2035848
20 Locked QAM256 31 579.0 -0.4 39.9 2363125 1084742
21 Locked QAM256 32 585.0 -1.7 39.4 2404174 1064535
22 Locked QAM256 33 591.0 -2.3 39.2 2510251 1179470
23 Locked QAM256 34 597.0 -2.5 38.8 2991239 1396847
24 Locked QAM256 35 603.0 -2.4 39.0 3541691 1520765
25 Locked QAM256 36 609.0 -1.9 39.1 5667496 1803588
26 Locked QAM256 37 615.0 -1.1 39.3 6424769 2385883
27 Locked QAM256 38 621.0 0.2 39.5 5643917 2359261
28 Locked QAM256 39 627.0 1.4 40.1 5290959 2347203
29 Locked QAM256 40 633.0 2.0 40.2 7573814 3777833
30 Locked QAM256 41 639.0 1.8 40.1 5488997 2118379
31 Locked QAM256 42 645.0 1.1 39.7 4593372 1978885
32 Locked OFDM PLC 48 688.0 -1.4 36.0 20404739 2263904


Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked SC-QAM 6 5120 17.3 47.3
2 Locked SC-QAM 7 5120 23.7 48.0
3 Locked SC-QAM 8 5120 30.3 48.8
4 Locked SC-QAM 9 5120 36.7 49.8
5 Locked SC-QAM 10 1280 41.2 52.8

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Re: frequent outages and DOCSIS disconnections

By the way, these numbers are right after a 1 minute outage today. I reset and channel 1-31 error counters went to zero.

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Expert

Re: frequent outages and DOCSIS disconnections

Don't sweat the OFDM channel.

 

The upstream power is on the high side and it may be intermittently fluctuating even higher to out of spec levels. There is an RF signal / line / connection impairment somewhere. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

 

Here are my boilerplate tips. If none of the below applies, then your only recourse is to get the techs involved again until the problem gets fixed properly.

 

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to get the techs re-involved as stated earlier. Good luck with it !.

 

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home.






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Re: frequent outages and DOCSIS disconnections

It's interesting you mention that the upstream power is on the high side. I have actually been playing around with inserting coax attenuators (nice ones from Pasternack). With zero dB of insertion loss I actually can't get the Motorola to work at all. The first tech that came said the downstream power levels were "way to high" though he didn't do anything about it. Adding 3dB at a time until 9dB greatly improved performance. If you're suspicious of high upstream power then I'll try a few more dB of attenuation. I still have plenty of downstream power margin.

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Expert

Re: frequent outages and DOCSIS disconnections

Nope. Don't do that !! Adding more overall type of attenuation will only make the upstream power even higher !! The power levels work opposite of each other. It's a balancing act. Additional overall attenuation will lower the downstream power but raise the upstream in the process.

 

You would need to use what they call a forward path only type of attenuator if you wanted to knock down the downstream power without affecting the upstream;

 

https://www.amazon.com/line-Signal-Forward-Attenuator-FPA6-54/dp/B07882H96R



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Re: frequent outages and DOCSIS disconnections

Thank you!

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Re: frequent outages and DOCSIS disconnections

Sorry, don't I want the opposite? To knock down upstream while maintaining downstream?

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Re: frequent outages and DOCSIS disconnections

And that's how you do it by using that forward path only type of attenuator that I linked. Remove any of those excess unneeded overall attenuators and try using the FPA only and see how the power levels turn out. Go from there



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Re: frequent outages and DOCSIS disconnections

Cool, just ordered a few.
Maybe I have my directions mixed up, but earlier you said my "Upstream power was on the high side". Upstream frequencies are 10-50MHz. The FPA datasheet shows ~0dB attenuation sub 50MHz (Upstream bands), and ~10dB above 50MHz (Downstream bands). This knocks down the Downstream (e.g. my downlink) and bandpasses the Upstream (e.g. my uplink).
So I'm trying to reconcile this with your first comment.

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Re: frequent outages and DOCSIS disconnections

By the way, I'm assuming that "Upstream power on the high side" means you're inferring that it is *too high and needs to be reduced*. Maybe that's where the miscommunication is.
I appreciate all the help.

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Expert

Re: frequent outages and DOCSIS disconnections

Right. So it doesn't raise the upstream which is too high already. Channel 5 is already out of spec !

 

Start from scratch. Remove all of the present attenuators and see what the power levels look like. The upstream power will surely go down and the downstream power will surely go up. See what is needed from there. Get the FPA and insert it and see where the power levels wind up. Experiment from there. As I stated earlier, it is a balancing act. The upstream power is preferred to be in the 40 to 45 dB area. The downstream power is preferred to be as close to 0 (zero) dB as possible.

 

I don't know how to be any clearer ?????? That'll be a case of Budweiser for my time................. 😜  😁 When in doubt, get a tech out again. Good luck !!



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Re: frequent outages and DOCSIS disconnections

Ah, I think I understand. The excess Upstream transmit power must be an issue not for the service provider but rather for the *modem* (perhaps saturation of modem power amplifier). This must be why I need to reduce the upstream power.
I'll get the FPA and try as you recommend. I also just hooked up my spectrum analyzer to the cable. I'm getting some crazy-high amplitude 60Hz noise and some other intermittent broadband noise. Something to investigate further if I'm still having issues.
I'll buy you a truck load of Budweiser if this works. The lost productivity alone would pay for it.
thanks

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Re: frequent outages and DOCSIS disconnections

A followup: the Forward Path Attenuator recommended worked great. perfect signal levels, no bit errors.

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Re: frequent outages and DOCSIS disconnections

Hope things hold up for you ! Good luck. Please start a new topic if you still have problems. Now closing this thread.



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