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Forum Discussion
Very slow Internet Download Speeds even after Xfinity repairs in my area
Even after Xfinity completed repairs in my area for performance related issues and even though I worked with Xfinity support, I continue to get extremely slow internet download speeds (about 10-20% of my provisioned speed).
Generally speaking, my upload speed via Speedtest.net have stayed well within my 20 Mbps provisioned speed. My download speed via Speedtest.net, which is provisioned for either 800 or 900 Mbps, dropped very low providing only 10-20% of my provisioned speed.
As I write this post, I continue to see these extremely slow speeds .
My cable modem is a Netgear CM1000.
Below are extensive details about the issue.
Cable Modem Details
Netgear CM1000
Logs (after rebooting the cable modem)
Note that the logs are captured across two images
Here are the logs in text format.
2024-12-20, 20:48:43 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 20:48:42 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3 .; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 20:48:41 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3 .; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:57:49 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:56:19 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:56 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:55 Critical (3) No Ranging Response received - T3 time-out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 16:49:52 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 15:52:02 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20, 15:50:57 Critical (3) Resetting the cable modem due to docsDevResetNow
2024-12-20, 15:31:06 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-20 15-30-01 Critical (3) Resetting the cable modem due to docsdevResetNow
2024-12-20, 12:57:14 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:27 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:26 Critical (3) No Ranging Response received - T3 time-out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:19 Critical (3) UCD invalid or channel unusable; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:23:19 Critical (3) SYNC Timing Synchronization failure - Loss of Sync; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:22:56 Critical (3) UCD invalid or channel unusable;CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1;
2024-12-19, 12:18:37 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:32 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:32 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:31 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:29 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:28 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
2024-12-19, 12:18:26 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing; CM-MAC=;CMTS-MAC=00:90:f0:5c:0a:00;CM-QOS=1.1;CM-VER=3.1
Connection Information
Note that the connection information is captured across two images
Timeline Details
Yesterday I received a text message at 12:17 pm from Xfinity stating that there were performance issues in my area and work was being done to revolves these issues.
Then, at 1:39 pm, I received a text message from Xfinity stating that the work had been completed.
Performance
Below are graphs showing results for speed tests using Speedtest.net, executed at the command line periodically to monitor my internet performance.
5 Day Performance
2 Day Performance
Detailed Speedtest Results
Here are a few Speedtest.net results from the above graphs with details and links.
12/20/2024 at 8:30 PM
https://www.speedtest.net/result/c/aa5d9da2-3027-4bcd-ade3-fdbc65f41b6e
12/20/2024 at 7:29 PM
https://www.speedtest.net/result/c/aa2bace2-7097-43ce-9d26-16dfa89ee45b
12/20/2024 at 6:30 PM
https://www.speedtest.net/result/c/4139107e-643f-47b2-bdff-843dce7250fa
14 Replies
Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended.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-Modems/m-p/1530376#M12853
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/- Xfinity said the power levels were fine and they attempted to reprovision the modem. I removed a splitter which didn’t help. A new coax cable arrives today which hopefully will help. If the new cable doesn’t improve performance at the current outlet, I intend to try it at a different one.
Paolo
pmb1976 wrote:
Xfinity said the power levels were fine and they attempted to reprovision the modem. I removed a splitter which didn’t help. A new coax cable arrives today which hopefully will help. If the new cable doesn’t improve performance at the current outlet, I intend to try it at a different one.
PaoloOf course Xfinity said the power levels were fine. They do not want to do anything. Xfinity's definition of fine for the power level and Netgear's definition are most likely something different. Check for yourself. See reference here:
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
Pay close attention to the first three sentences at the top.
Repeat question: What is the brand name and model number of your router?
Repeat question: What is the brand name and model number of the device you are running the throughput tests on?
Recommend you use the installable Ookla stand alone application to measure throughput. It appears you are using a web browser and the Ookla web address. This later approach introduces inaccuracies based on the web browser.
The application is available in the Microsoft store or the play store.
What is the brand name and model number of the router you are using?
What device are you running the web browser on for testing?
- Hi,
The speed tests are run using the Ookla provided command line tool. I've run speed test using the Ookla application with similar results. I've been running periodic automated speed test for several years (see graphs for what I mean) without issue.
The cable modem is a Netgear CM1000.
I received abrand new RG6 coax cable today. I replaced the existing coax cable running to the cable modem with this new one. The speed test results were in line with previous results and very poor. I then moved the cable modem to the basement where the cable feed comes into the building. There was a splitter connecting to a cable going into the wall with a spare port open. I connected to that port.
The speed test results were the similar to previous poor results. Here are two runs using the Ookla Speedtest app using the set up in the basement:
https://www.speedtest.net/my-result/d/40e10466-758d-4d05-b41f-51085293c74f
https://www.speedtest.net/my-result/d/f3df538d-d119-4d05-a7c6-9f050fccb75a
The equipment used in the basement is:
- New RG6 coax cable
- Surface Laptop (with USB 3.0)
- CAT 5e Ethernet cable
- Anker 1000 MB USB Ethernet Dongle
- Netgear CM1000
The Surface was plugged directly into the cable modem (no router).
I've used this equipment before (minus the new coax) and have gotten much, much faster results.
Combined with the fact that my neighbor ran a speed test for me yesterday and he got his provisioned speed for 600 Mbps using his Xfinity XB6 (I think it was that; it was definitely an XB devices), it tells me that the issue is unlikely related to the wiring in my building. I've seen issues where Comcast pushes a new configuration file to modems or updates the CMTS configuration, causing compatibility issues with cable modems, usually 3rd party ones.
I can't update the original ticket. Here are higher quality images.
Cable Modem Details
Netgear CM1000
Logs (after rebooting the cable modem)
Note that the logs are captured across two images
Connection Information
Note that the connection information is captured across two images
Performance
Below are graphs showing results for speed tests using Speedtest.net, executed at the command line periodically to monitor my internet performance.
5 Day Performance
2 Day Performance
Detailed Speedtest Results
Here are a few Speedtest.net results from the above graphs with details and links.
12/20/2024 at 8:30 PM
https://www.speedtest.net/result/c/aa5d9da2-3027-4bcd-ade3-fdbc65f41b6e
12/20/2024 at 7:29 PM
https://www.speedtest.net/result/c/aa2bace2-7097-43ce-9d26-16dfa89ee45b
12/20/2024 at 6:30 PM
https://www.speedtest.net/result/c/4139107e-643f-47b2-bdff-843dce7250fa
What was the interval of time you used between the throughput tests?
- 1 hour
You mentioned Xfinity attempted to re-provision your modem. What happened?
- Nothing. Same as before
Have there been any recent driver or firmware updates on your computer?
- No, there haven't
One thing to check is the network profile on your computer. It should be private and not public. I have seen Windows updates that changed the profile as part of the update process.
- Yes, it's private. The issue happens with two separate computers: a laptop and a desktop
Your modem connects to a node through the coax cable. The node is where the signals are converted from a fiber optic connection to the coax signal. It is possible to saturate a node with repeated throughput tests.
Any time you boot up a device like a computer, it is subject to updates for drivers and firmware for a variety of systems. Microsoft does this at least twice a month and often daily. Your computer OEM also provides updates, but they are not usually forced on you like from the operating system. It would not hurt to verify with the OEM if the drivers/firmware for your Ethernet ports are current.
A stand alone modem has few if any settings you can adjust. I cannot see your re-posted images because a moderator has not approved them yet.
Hi,
After a good amount of troubleshooting, my cable modem is now consistently getting 700 Mbps download and 5 Mbps upload. That's a great improvement from before but not the speeds I'm paying for.
In speaking to Xfinity support, I found out that my cable modem (Netgear CM1000) is getting a "default" bootfile rather than the bootfile for my speed tier, namely Superfast which is rated for 800 Mbps download/20 Mbps upload. The Xfinity support representative indicated to me on the phone that the system does *NOT* provide her the ability to select the Superfast speed tier for my Netgear CM1000 and that's likely because the Netgear CM1000 isn't approved for that speed tier.
However, Netgear CM1000 does support the speeds for the Superfast speed tier.
"Certified with Xfinity with speeds up to 800Mbps, Spectrum service of 1Gbps, and with Cox service speeds of 1Gbps. Please check your cable Internet service provider website data speed tier compatibility (not compatible with Cable bundle voice services).Wireless router not included."
Source: https://www.netgear.com/home/wifi/modems/cm1000/
Additionally, I have had this modem for 5 years and, only until recently, I have been getting well above the 800 Mbps. Here is the last year of speed test results using SpeedTest.net:
Some of the performance issues as of late have, at least in part, been due to wiring issues and outages, etc.
This seems like a possible change in Xfinity's policies with regards to the Netgear CM1000. Is Netgear aware of this? Assuming that representative's from Netgear monitor this forum, can a Netgear representative confirm (or not) that the Netgear CM1000 is no longer supported on Xfinity's network for the Superfast speed tier (800 Mbps Download/20 Mbps Upload)?
Thanks,
Paolo
Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended.
What is the brand and model of the host wifi router connected to the modem?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-Modems/m-p/1530376#M12853
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/
