C6900 periodic poor download/upload speeds

[ossodiseppia]

I have been having issues with download/upload speeds for a number of weeks.  When I do the speed test, the numbers are all over the place.  I had a Comcast tech out week before last.  I was told he is a senior tech and works mostly on the business side.  So, I felt comfortable that he knows what he's doing.  He checked things at the box where all of the homes in my neighborhood are hooked up.  He checked the connection that comes out of the ground and then cable that comes into my home all the way to the modem.  He determined that the modem is failing and that he'd seen a fair number of "these" that failed right out of the box.  So, I bought a new modem/router, but have not hooked it up.  I'd like to get an opinion from the smart folks before I go through the hassle of installing a new modem and reconfiguring my network and all of the attached devices.

The log file indicates a timing synchronization failure at the modem.  There is also mention of another MAC address (CMTS).  I cannot find this MAC address on my network, anywhere.

If I've left something out that would help, please let me know.  I know nothing about these gizmos.  Thank you.

[michaelkenward]

The C6900 is a cable modem/router.

While many questions about routers are generic and could be answered anywhere, some things need specialist knowledge.

You might get more help, and find earlier questions and answers specific to your device, in the appropriate section for your hardware. That's probably here:

Cable Modems & Routers

You might like to search there for messages related to your problem.

I will ask the Netgear moderator to move your message.

In the meantime you could visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware. Look at the label on the device for the model number.

Check for various troubleshooting tips.

You may have done this already. I can't tell from your message.

I mention it because Netgear stopped supplying printed manuals and CD versions some years ago and people sometimes miss the downloads.

[ossodiseppia]

Thank you for the reply and pointing out I posted in the wrong forum.  I am sorry about that.  I don't normally make that kind of mistake.

I have consulted the Netgear site for solutions.  They offer nothing related to troubleshooting other than referring folks to their ISP.

I've also found a couple of other posts regarding this same issue, but it's not very clear to me, that the issue is related to the line of modem/router.

[michaelkenward]

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@ossodiseppia wrote:

Thank you for the reply and pointing out I posted in the wrong forum.  I am sorry about that.  I don't normally make that kind of mistake.

---

Easily done, especially given the messy nature of this place.

I just wanted to point you in the direction of messages that might cover your hardware.

[ossodiseppia]

I appreciate the help.  I looks like my thread has been moved.  Hopefully, Ill get some feedback.

I'm just about done getting the new modem/router set up.  I have a few things that require a fixed IP.  So, this gave me an opportunity to put them all next to each other. 

I am still getting these strange errors, even on the new modem/router.  It's funny, they have a date of 1970-01-01.  It's bugging me and I hope someone will chime in.

[FURRYe38]

I see lots of Criticals in the Event log that the ISP needs to review and resolve.

Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/

[ossodiseppia]

Thank you for the reply.  This is all very common sense stuff for a tech.  But, the tech I had out here about ten days ago, appears to not know his #$% from a hole in the ground.  He did many of the things that you have suggested.

The gentleman that was here this afternoon, within minutes, determined that the line from the "tap" to my house was faulty.  My house was built in 1998/1999 and it was built with a cable from the "tap".  The cable was run through conduit, underground.  I now have a new cable strung across my flower bed.  I am very tempted to try and pull a new line through the conduit as I don't want a cable "buried" in my flower bed just a couple of inches below the surface.  My 24 year old house has a mature yard.  It will be nearly impossible to bury a cable.

What really pi$$es me off, is that I bought a new modem/router based off the recommendation of the first tech.  I think I'm gonna call Comcast and whine.  Before I do that, I'm going to try my "old" modem and see how things go.

I'll be monitoring the event log and speed over the next days to make sure things are ok.

To be continued......

[michaelkenward]

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@ossodiseppia wrote:

But, the tech I had out here about ten days ago, appears to not know his #$% from a hole in the ground. 

---

There's a surprise. You might not be surprised by the number of people who turn up here after being led astray by their ISP's tech support.

The least you could do is to demand a rebate on your subscription.

[ossodiseppia]

I received a credit of $45 before the first guy came out.  I plan to see what I can get out of them, today.

Below is a screen capture of the event log from the new modem.  It seems to look better.  The critical messages are from before the new tap cable was run.  I'll give it a few days before I declare things good to go.

[FURRYe38]

Still see Criticals. 

Please post a full screen capture of the Cable Connections page as well. 

[ossodiseppia]

I've ditched the C6900.  I bought a CAX30 and have been using it for about a week.  If I need to start a new thread, I'd be happy to.

This CAX30 Modem/Router has a Speed Test option.  I don't know if the test runs between a server somewhere in lala land and my modem or, if it runs the test between some server in lala land and the PC from which I perform the test.

Either way, the speed is appalling crappy.  I have gigabit service from Comcast

If I run a speed test through my internet browser I get the results below.  I would expect to get different speeds from different servers.

These tests were run on my desktop that uses ethernet.  It has a gigabit network card.  My home network is wired with CAT 5E and I have a managed gigabit switch.

 

Cable Diagnostic
Startup Procedure
CM status: OPERATIONAL
DownstreamChannel: 543000000Hz Locked
ConnectivityState: OK operational(12),
BootState: OK Operational
Security: Enabled
IPProvisioningMode: 12 IPv6Only

Downstream Bonded Channels
Channel LockedStatus Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked 256 QAM 20 543000000 Hz 0.5 dBmV 39.4 dB 0 0
2 Locked 256 QAM 17 525000000 Hz 0.6 dBmV 39.3 dB 0 0
3 Locked 256 QAM 18 531000000 Hz 0.6 dBmV 39.3 dB 0 0
4 Locked 256 QAM 19 537000000 Hz 0.4 dBmV 39.4 dB 0 0
5 Locked 256 QAM 21 549000000 Hz 0.5 dBmV 39.4 dB 0 0
6 Locked 256 QAM 22 555000000 Hz 0.1 dBmV 39.5 dB 0 0
7 Locked 256 QAM 23 561000000 Hz 0.1 dBmV 39.6 dB 0 0
8 Locked 256 QAM 24 567000000 Hz 0.1 dBmV 39.6 dB 0 0
9 Locked 256 QAM 25 573000000 Hz 0.0 dBmV 39.6 dB 0 0
10 Locked 256 QAM 26 579000000 Hz 0.2 dBmV 39.6 dB 0 0
11 Locked 256 QAM 27 585000000 Hz 0.5 dBmV 39.5 dB 0 0
12 Locked 256 QAM 28 591000000 Hz 0.3 dBmV 39.5 dB 0 0
13 Locked 256 QAM 29 597000000 Hz 0.2 dBmV 39.6 dB 0 0
14 Locked 256 QAM 30 603000000 Hz 0.1 dBmV 39.7 dB 0 0
15 Locked 256 QAM 31 609000000 Hz 0.2 dBmV 39.6 dB 0 0
16 Locked 256 QAM 32 615000000 Hz 0.1 dBmV 39.6 dB 0 0
17 Locked 256 QAM 33 621000000 Hz 0.0 dBmV 39.6 dB 0 0
18 Locked 256 QAM 34 627000000 Hz 0.2 dBmV 39.7 dB 0 0
19 Locked 256 QAM 35 633000000 Hz 0.3 dBmV 39.7 dB 0 0
20 Locked 256 QAM 36 639000000 Hz 0.3 dBmV 39.7 dB 0 0
21 Locked 256 QAM 37 645000000 Hz 0.3 dBmV 39.7 dB 0 0
22 Locked 256 QAM 38 651000000 Hz 0.4 dBmV 39.6 dB 0 0
23 Locked 256 QAM 39 657000000 Hz 0.3 dBmV 39.6 dB 0 0
24 Locked 256 QAM 40 663000000 Hz 0.2 dBmV 39.7 dB 0 0
25 Locked 256 QAM 41 669000000 Hz 0.4 dBmV 39.7 dB 0 0
26 Locked 256 QAM 42 675000000 Hz 0.3 dBmV 39.3 dB 0 0
27 Locked 256 QAM 43 681000000 Hz 0.0 dBmV 39.6 dB 0 0
28 Locked 256 QAM 44 687000000 Hz 0.1 dBmV 39.5 dB 0 0
29 Locked 256 QAM 45 693000000 Hz 0.1 dBmV 39.5 dB 0 0
30 Locked 256 QAM 46 699000000 Hz 0.1 dBmV 39.5 dB 0 0
31 Locked 256 QAM 47 705000000 Hz 0.1 dBmV 39.4 dB 0 0
33 Not Locked Unknown 0 0 Hz 0.0 dBmV 0.0 dB 0 0

Upstream Bonded Channels
Channel LockedStatus ChannelType Channel ID SymbolRate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 10400000 Hz 41.5 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 16400000 Hz 40.8 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 40.8 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 29200000 Hz 40.8 dBmV
5 Locked ATDMA 5 5120 Ksym/sec 35600000 Hz 39.8 dBmV
6 Locked ATDMA 11 5120 Ksym/sec 40400000 Hz 40.3 dBmV
7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0 dBmV
8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0 dBmV

Downstream OFDM Channels
Channel Channel ID Frequency Power SNR/MER ActiveSubcarrier Correctable Uncorrectable
1 48 805000000 Hz 1.1 dBmV 37.7 dB 1108 ~ 2987 102654659 0
2 0 0 Hz 0 dBmV 0 dB 0 ~ 0 0 0

Upstream OFDMA Channels
Channel UpstreamMuted RangingStatus Subc Zero Freq ActiveSubcarrier SymbolsPerFrame Power
1 n/a Other 0 MHz 0 ~ 0 0 0 dBmV
2 n/a Other 0 MHz 0 ~ 0 0 0 dBmV

In 2019, I ran the cable from the modem to the cable box on the outside of my house.  That cable has been tested by the first guy.  And, he checked everything from my modem/router to the tap box.  The second guy replaced the cable from the tap box to my house.

At this point, I don't really know what to do.  I've had two guys out here.  Late last night I was streaming live TV and I noticed a tiny bit of buffering.  I think that might be reflected in the log.

As of right now, the service that I am getting is ok.  There is no way I need gigabit service.  But, it's what I get as part of the service package from Comcast.  If I downgrade my internet service, it really doesn't affect the monthly price.