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

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@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.

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 !

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...

All 3 upstream at 49.0 dBmV

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-levels/td-p/3282853

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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@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?

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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.

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. 

@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!

I recently upgraded to Gigabit service but am not achieving the advertised speeds.  I read in a post that GB is only offered with DOCSIS 3.1 mode.  My modem was provisioned using all 32 channels in QAM256 instead of OFDM.  How can I get this corrected?

@Saelig66 

Please create a new topic of your own here on this board detailing your issue. Thanks. Year old dead now being closed.