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DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

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DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

High level issue: Was having internet issues. Comcast support said my old SB6121 "is not supported" and was the issue.  Didn't beleive them, but after 10 years of use, I've got my money's worth.  Wasn't able to get my full 200Mbps Blast speed anyways.  So, I order a new DOCSIS 3.1 modem and got talked into upgrading to the New Gigabit internet plan for a meesly extra $20/month.  Too good to be true, right?  Right.  Consistently getting less than HALF that (high 300s, 400-500Mbps max) even though my signal stats are well within spec.  Upstream is pretty rock solid 40+ Mbps, with no lag time.  On site tech says everything checks out.  Must be an issue with my (new) modem.  I think it's an issue with provisioning, though I'm open to a well thought out explaination why I may be wrong. 

Details you will ask me about:
Modem - Arris model SB8200 - Hardware version 6

    Software version - AB01.01.009.32.01_122319_183.0A.NSH
Direct wired connection.  All power levels look good. 
32 downstream channels - Locked

Modulation - QAM256

POWER - between -1.7 and +.4 dBmV

SNR/MER - between 39.8 and 41.8 dB

corrected and uncorrectables seem to be all over the place

 

Had a Comcast tech out to the house.  All internal lines look good.  Said outside line tests good, except the mouse hanging out in the box and an older cable that's a little long (box to house).  He said he "Will talk with someone about replacing it."  Don't much trust his expertise, since he didn't know much about public IP provisioning (I have a secondary issue that needs resolved concerning my Comcast security system).  Of note, he said my speeds would keep going up if I were to run a longer speed test, so it "looks fine" to him.  He also thinks modems don't have IP addresses, and that's only handled by your router.  I just said "OK", as I didn't feel like explaining it to him the differnece between Public and private IP's.  It was obvious he wouldn't be much help.  He said it was my modem and to pick up an XB6 from the comcast store.  I'd rather just provision my DOCSIS 3.1 modem appropriately.  Something that sticks out to me, I thought you could only get gig speed tier via the DOCSIS 3.1 / OFDM downstream channel, not the other 32 DOCSIS 3.0 QAM 256 channels.  Though, my modem lights up blue on the downstream, indicating DOCSIS 3.1.

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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)


@Duanebs86 wrote:

 

 Upstream is pretty rock solid 40+ Mbps, with no lag time. 
40 up indicates that the correct cofiguration file / boot file is being pushed to the modem.
Details you will ask me about:

Modem - Arris model SB8200 - Hardware version 6

    Software version - AB01.01.009.32.01_122319_183.0A.NSH
Direct wired connection.  All power levels look good. 
32 downstream channels - Locked

Modulation - QAM256

POWER - between -1.7 and +.4 dBmV

SNR/MER - between 39.8 and 41.8 dB

corrected and uncorrectables seem to be all over the place

 

The downstream power levels and the SNR's are all in spec. Please also post the upstream power level values.

 

He also thinks modems don't have IP addresses, and that's only handled by your router.  I just said "OK", as I didn't feel like explaining it to him the differnece between Public and private IP's.

 

Straight cable modems like the SB8200 do not get assigned public / WAN IP addresses. They are layer 2 bridges that bridge the Comcast assigned public IP to the device that is connected to their ethernet port. They do however get an obscure IP addy assigned to them from the ISP for the purpose of back door management / maintenance. Combo gateway devices with a built-in router component and stand-alone routers do.

 

Something that sticks out to me, I thought you could only get gig speed tier via the DOCSIS 3.1 / OFDM downstream channel, not the other 32 DOCSIS 3.0 QAM 256 channels.  Though, my modem lights up blue on the downstream, indicating DOCSIS 3.1.

 

Gig speed is delivered only via the DOCSIS 3.1 / OFDM downstream channel. And the blue light is correct if there are multiple bonded DOCSIS 3.0 channels present. It does not indicate 3.1.

 



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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

All 3 upstream at 49.0 dBmV

Channel Channel ID Lock Status US Channel Type Frequency Width Power
1 39 Locked SC-QAM Upstream 24000000 Hz 6400000 Hz 49.0 dBmV
2 37 Locked SC-QAM Upstream 36800000 Hz 6400000 Hz 49.0 dBmV
3 38 Locked SC-QAM Upstream 30400000 Hz 6400000 Hz 49.0 dBmV


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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

Downstream Bonded Channels
Channel ID Lock Status Modulation Frequency Power SNR/MER Corrected Uncorrectables
33 Locked QAM256 477000000 Hz 0.4 dBmV 41.6 dB 7 26
1 Locked QAM256 531000000 Hz -0.4 dBmV 41.2 dB 27 0
2 Locked QAM256 537000000 Hz -1.1 dBmV 40.9 dB 7 28
3 Locked QAM256 543000000 Hz -1.1 dBmV 41.0 dB 6 29
4 Locked QAM256 549000000 Hz -1.5 dBmV 40.8 dB 15 19
5 Locked QAM256 555000000 Hz -1.6 dBmV 40.7 dB 6 29
6 Locked QAM256 561000000 Hz -0.9 dBmV 41.1 dB 12 21
7 Locked QAM256 567000000 Hz -1.1 dBmV 41.1 dB 15 19
8 Locked QAM256 573000000 Hz -0.9 dBmV 41.2 dB 29 0
9 Locked QAM256 579000000 Hz -1.4 dBmV 40.9 dB 5 30
10 Locked QAM256 585000000 Hz -1.7 dBmV 40.9 dB 29 4
11 Locked QAM256 591000000 Hz -1.1 dBmV 41.1 dB 12 22
12 Locked QAM256 597000000 Hz -1.2 dBmV 41.1 dB 14 19
13 Locked QAM256 603000000 Hz -1.2 dBmV 41.0 dB 32 0
14 Locked QAM256 609000000 Hz -1.4 dBmV 41.0 dB 12 22
15 Locked QAM256 615000000 Hz -1.3 dBmV 41.2 dB 20 13
16 Locked QAM256 621000000 Hz -0.8 dBmV 41.4 dB 10 24
17 Locked QAM256 627000000 Hz -0.9 dBmV 41.4 dB 4 32
18 Locked QAM256 633000000 Hz -0.9 dBmV 41.4 dB 10 23
19 Locked QAM256 639000000 Hz -0.7 dBmV 41.5 dB 27 0
20 Locked QAM256 645000000 Hz -0.2 dBmV 41.8 dB 32 0
21 Locked QAM256 651000000 Hz -0.1 dBmV 41.7 dB 7 27
22 Locked QAM256 657000000 Hz -0.4 dBmV 41.7 dB 8 25
23 Locked QAM256 663000000 Hz -0.4 dBmV 41.7 dB 10 23
34 Locked QAM256 507000000 Hz -0.1 dBmV 41.5 dB 24 9
35 Locked QAM256 513000000 Hz 0.0 dBmV 41.4 dB 31 0
36 Locked QAM256 519000000 Hz -0.2 dBmV 41.3 dB 6 26
37 Locked QAM256 525000000 Hz -0.7 dBmV 41.0 dB 18 15
38 Locked QAM256 483000000 Hz 0.4 dBmV 41.5 dB 29 1
39 Locked QAM256 489000000 Hz 0.3 dBmV 41.6 dB 6 28
40 Locked QAM256 495000000 Hz -0.4 dBmV 41.2 dB 8 26
41 Locked Other 762000000 Hz -0.3 dBmV 39.8 dB 1002422419 0
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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

This may not be the direct cause of your speed problem, but the upstream power is almost out of spec (too high) and it may be intermittently fluctuating even higher to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems. It should be addressed as it may be another problem just waiting to happen if it isn't already.

 

Since you've already had a tech visit, you should get the techs re-involved until it is corrected properly ! Good luck with it !




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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

Thanks, on the phone with them again.  Resetting and testing from the beginning bc everyone at Comcast has amnesia pertaining to my previous, still unresolved issue...

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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

Well, another tech will be here in the AM.  Hopefully this guy replaces the line from the pole, as it's the only thing NOT new in my setup at this point.  In the meantime, something just doesn't sit right with me.  There are numerous examples of folks with their own modems running into the same issue.  All of the topics on these forums are locked out before a resolution, or the person switches to a rented modem.  While $10/month is the easy button, I'd rather find an actual resolution that can set the midwest free of cable modem rental fees!


This guy looks to have similar setup, though upsteam issues (mine are only downstream)... https://forums.xfinity.com/t5/Your-Home-Network/Arris-SB8200-upstream-not-bound-to-DOCSIS-3-1-power-...

It was mentioned that the blue light on the SB8200 doesn't reflect DOCSIS 3.1, but rather bonded DOCSIS 3.0 channels.  I THOUGHT that QAM 256 maxed out at 400Mbps... which reflects the actual speeds I'm getting at the moment.  Is that 400 Mbps per channel, so bonded could theoretically be much higher?

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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)


@Duanebs86 wrote:


It was mentioned that the blue light on the SB8200 doesn't reflect DOCSIS 3.1, but rather bonded DOCSIS 3.0 channels.  I THOUGHT that QAM 256 maxed out at 400Mbps... which reflects the actual speeds I'm getting at the moment.  Is that 400 Mbps per channel, so bonded could theoretically be much higher?


The total bandwidth / speed capability depends on how many channels are bonded together.

 

A  current, single 256 QAM modulated, 6.4 MHz wide, 5.120 MSym/sec downstream cable channel supports a raw data rate of approximately 43 Mbps, and a real world throughput of approximately 38.1 Mbps.

 

Example: 32 x 38 = 1216 theoretical speed.

 

 



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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

Thanks for the additional info.

I had a 2nd tech out.  He found a crack in the line's casing where water had been leaking in and causing corrosion.  Replaced the whole run from my house to the pole.  Said he'd reprovision my modem as well and my issues should be resolved after a reboot.

My jitter issues seem to have vanished, but my speeds are still hovering around 4-500 Mbps.  Hardwired of course, and now using the speed test app (the comcast speedtest only gives 2-300 Mbps from the same device. 

I compared my channel setup with a friends XB6, and everything seems setup correctly on my end.  Actually, better power levels and ranges than his.  He got frustrated and traded in his modem for a rented one and magically his issues were resolved.  I'm feeling like Comcast is pulling some sort of fast one on me... and I'm fairly close to just switching over to AT&T. 

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Re: DOCSIS 3.1 Modem not provisioned correctly (DOCSIS 3.0 QAM 256 Channels vs DOCSIS 3.1 / OFDM)

@EG This is interesting information to use for at-a-glance troubleshooting. Do you mind sharing your source for the blue light meaning? The SB8200 User Guide (p. 12 August 2016) offers a the following explanation: Blue*: High-speed Internet connection with down/upstream channels in DOCSIS 3.1 mode. However, the Quick Start Guide (p. 3 November 2019) only says Blue* (ON): indicates a bonded downstream (receive data) channel connection. It would be nice if you can dispell the confusion by providing an authorative source.

Thanks!