Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem

Hello and thank you for reaching out to us here on the Forums! I can definitely understand the frustration if your internet speeds are intermittent. I would love the opportunity to help you resolve this concern and I'd like to get a look at the signal levels here on our end as well. Please click on my handle "ComcastBillie" and send us a private message with your full name and address to get started.

The signal stats are o/k but the error log entries indicate that something is going on. Perhaps there is noise ingress into the line(s) somewhere.

There are other signal stat figures that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.

I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They will be able to poll the CMTS to see whether or not everything is in the green zone, see your node / cable plant and modem health, and also see a history plot for the modem. You should get a reply here in your topic. Good luck !

To bring folks on this forum uptodate with the private message history related to this issue I have included the emails in this post that I sent to comcast customer service who have been GREAT thru this process.

To: ComcastRayana
Sent: ‎02-27-2021 09:14 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem

Sorry for not providing closure.

The terminators did arrive. However, I received an unexpected message from Comcast in myAccount app when I pressed the troubleshoot internet before installing the terminator caps.

I pressed the troubleshoot internet prior to installing the caps to the remaining 5 open cable ports on my powered splitter.
The MyAccount application reported that an outage issue has just been fixed affecting my service and several other customers even though previous outage checks have always indicated "there were no issues and everything looks good!"

I ran speed test on my WiFi and got 405Mbps with my iPhone 11 !!!!. Verified download of several other devices was also back to normal. Ran some wire shark traces.
Stable consistent low ping timings. Signal levels on cable modem all look the same when getting 24Mbps so as I suspected this was not an issue with my cable modem nor my cabling.

Someone found and fixed something within the Comcast infra structure that ultimately fixed my slow download speed!!!!!
Can someone from Comcast post what was the root cause that was fixed?

I did install the caps but didn’t notice change in the reported signal levels. The download performance remained good!!!

Problem had been solved but don’t know what the outage issue was nor what changes were made to Comcast infrastructure internally that resulted in fixing my performance issue but my issue is fixed!

Regards, [Edited, PII]

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To: ComcastDaryl
Sent: ‎02-19-2021 08:45 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Let’s hold off sending the gateway modem. I turned off IPV6 , disabled dns query, and disabled ping use to check connectivity even if 120 Sec just to reduce traffic.
I got 374 Mbps downloads but also got connection failures which I traced to unexpected WAN port close and restart as reported by the router.
This is the same issue with the direct PC which got 430Mbps but with network connection drops.

Contacted ARRIS who said their logging only shows human readable product info for cable side of modem not Ethernet port.
The ARRIS technician saw the upstream power was only 38 which is not within spec for SB8200 which expects min of 45!
I ordered a couple of cable 75ohm coax cable terminators. This may address signal reflection and modem signal harmonics noise.
Will let you know the results when the terminators arrive.

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To: ComcastKatieMS
Sent: ‎02-18-2021 08:04 PM
Read: ‎02-18-2021 09:08 PM

The 24 Mbps download speed is still occurring. Please send out the gateway. Does the gateway have an ethernet port so I can connect it to my existing WiFi network?

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To: ComcastKatieMS
Sent: ‎02-18-2021 07:56 PM
Read: ‎02-18-2021 09:09 PM

I reconfigured my router to use its 2.5 Gb port as the WAN port. The SB 8200 only has a 1 Gb port so it should negotiate down to the 1 Gb speed. Rebooted the SB8200 and then reconnected the cable and port.

What does TLV 11 Error Configuration File invalid format mean? I have been seeing this in the cable modem log since Jan 2021 (prior to the latest download speed issue)?

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To: ComcastTambrey
Sent: ‎02-18-2021 12:46 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Can you send just a cable modem to minimize the variables while troubleshooting? Do you know of any SB8200 specific network port issues? I am going to move the WAN from the WAN port on GT-AX11000 to other ports to see if there is noise in cable negotiation speed. The direct pc forced 1Gbps link to cable modem which it should have handled. The cable is cat5e not cat6 like I thought o had used. It is rated at 1g but never know as it ages.

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To: ComcastTambrey
Sent: ‎02-17-2021 10:20 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Good news and bad news on direct modem test with no router. Good news running Speedtest.xfinity.com the download indicated 371Mbps. This is what I expected to see. Ya. Bad news Running upload test to speedtest.xinfinity.com returned a connection error initially by continued and returned expected 24Mbps. Running the www.speedtest.com on direct connection to modem started showing 8 Mbps and climbed to 10Mbps which is worse than with Wi-Fi routers but probably not statistically significant. However, repeated attempts actually resulted in connection failures being reported. Which is really bad. Stability and compatibility is better than slow. Cant test anymore tonight. Have conference calls and astronomy stuff to do tonight. Wi-Fi and routers are back on live. Noticed IP reservation time appeared to change to hours from days. Is that because of diagnostics?

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To: ComcastMarcos
Sent: ‎02-17-2021 07:41 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Back online.

Ran quick speed test over WiFi 5GHz and still see 10 ms ping, 24.67 Mbps download and 23.70 Mbps upload.

I can run directly to the modem in a little while. Have to make sure wife is not on facetime with a patient as the network change over from Wifi to cellular isn't always clean.

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To: ComcastMarcos
Sent: ‎02-17-2021 06:51 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Several of the devices are security camera which use the upload (24Mbps bandwidth) and very very little of the download. I am semi retired. When I was working full time , I worked for Citrix developing and supporting the mobile and virtual desktop/app stuff. So there were lots of VPNs active with screen remoting especially when I was working with customers on product issues. ( I can relate). I was using more of the download bandwidth. We had 200Mbps and it was just sufficient. But will probably find something to work on which will still need 600Mbps bandwidth so don't need to downsize...

I can selective block devices on my LAN with the ASUS AIMesh console.

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To: ComcastMarcos
Sent: ‎02-17-2021 06:33 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem

There is 33 devices connected to my WiFi LAN. Four of those devices are ASUS router nodes in an ASUS AIMesh configuration.

The master ASUS router node of the AIMesh is a GT-AX11000 which is connected to the ARRIS SB8200 Cable Modem. Of the 33 devices, the master ASUS router and will about 25 of the other devices. Two of the devices are TVs which may run NetFlix streams. The other 23 devices only asynchronously send/receive 100k at a time at most. When a www.speedtest.net is run on an iPhone , what ever performance is occurring is reliably reproducible. GT-AX11000 routers are spec'd at 10Gbps aggregate performance (only seen 6Gbps) to clients. These are tri band routers. most devices are on 2.4GHz band channels. There are two 5GHz bands.

When cable performance is working, I see between 350Mbps to 400Mbps using an iPhone 11 with www.speedtest.net even though sites document their max thruput at 250Mbps.

You can send a reset signal . The devices are not doing anything critical. Thanks for asking. Shows sensitivity. ;^) I still use the old school emojis.

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To: ComcastMarcos
Sent: ‎02-17-2021 05:50 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
Hi, Love your continuous support model. The MyAccount app should keep track off issue disposition and refer user to the forum or integrate forum web support in MyAccount app. I am current on my LAN but not near my modem. What did you want me to try? I have rebooted it several times. I have disconnected all cables and rebooted it. I have also disconnected all cables and pressed the reset switch to enable factory settings. I have disconnected all conectors and reconnected and tightened them.

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To: ComcastTambrey
Sent: ‎02-17-2021 05:09 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
One other thing. There was mention of a default modem class if your modem doesn’t support your performance pier. What is the download speed of that tier and is it possible that my modem is mistakenly being set to that resulting in 20Mbps instead of 600Mbps?

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To: ComcastTambrey
Sent: ‎02-17-2021 05:02 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
In the forum there was mention of looking at Comcast side of cable modem connection for SNR and power that you see on your end. Can network traffic route from/to my cable modem get tagged and analyzed internally for any congestion or routing issues that could account for the performance drop? The outage map shows the neighborhood next to my neighborhood (same area code) has an issue with channel outage affecting X number of users. There is a green all good map indicator at my property. Could that adjoining issue affect my connections? It is always appearing when my performance drops. Can you see what that outage indicates and why does it appear in addition to the all good indicator? What does TLV 11 error bad conf file mean? Appears since 2021 even though this issue symptom has occurred thru 2020. Please send someone out

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To: ComcastJosephW
Sent: ‎02-17-2021 03:32 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem

WireShark is a staple troubleshooting tool. Long history with computer networking. In 1980's , I fixed some issues in the original TCP/UDP/IP networking protocol in the original BSD 4.1a release.

I haven't set up port forwarding features yet. Just hardcoded the primary and secondary DNS that are used by my router and clients instead of using the defaults from WAN connection. The DNS that Comcast at that time was > 20 hops away. The google DNS address was reliably 8 hops so there was a noticeable reduction new socket connection setup time which appeared to contribute to connection drops. I am not seeing connections dropping. Just slow so I haven't altered the DNS configuration in over a year.

Use the 10ft CAT6 cable that typically connects the Cable Modem to the GT-AX11000 router as the direct connection tp the router.

Regards,
[Edited, PII]

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To: ComcastBillie
Sent: ‎02-17-2021 03:01 PM

Re: Frequent 20Mbps download speed on a 600Mbps plan with SB8200 ARRIS Cable Modem
You are currently only able to receive 20 Mbps download correct?

Correct.

Are you using a stand alone router and can you tell me what troubleshooting steps you've already taken?

WireShark, Ping, TraceRoute, Checked speed to multiple destinations with www.speedtest.net Last year , there were connections dropping in addition to the performance drop. I mitigated the connection drops by specifying primary DNS as 8.8.8.8 (google) instead of 75.75.75.75. After the performance issue magically fixed itself , I removed the hardcoded 8.8.8.8 DNS server setting.

I posted the SB8200 status and error log in the original post alone with ping and trace route. The trace route seemed to take a little longer and had two timeout. The ping seemed ok. There was a configuration file error message in the SB8200 Error log.

Is this over Wi-Fi or while connected directly via an Ethernet cable?

Currently, I see 20Mbps with WiFi and when connected directly to the SB8200 Cable Modem.

In the past, I have seen 40Mbps when connected directly to the SB8200 Cable Modem after seeing 20Mbps on WiFi connection to ASUS GT-AX11000 router that is directly connected to SB8200 Cable Modem using its WAN port.

I received a response from Comcast on 2/27/21 to my last post on 2/27/21 that they were going to look at the details concerning the previously unannounced "outage" that was affecting my service which has now been fixed. Whatever comcast fixed , ultimately fixed my download performance since all previous changes didn't!!

Unfortunately, I have not received any details regarding what the root cause of the outage was nor any details on what was fixed to resolve the outage. I didn't follow up because I was now enjoying my internet peformance...

What is given can be taken away . . .

Yesterday (3/3/21), I had noticed some internet delays so launched MyAccount app to reboot my modem, however, MyAccount app reported a current outage (something to do with "missing channels") that was affecting my internet service. Surprisingly, speedtest  showed 375Mbps iPhone 11 WiFi performance so didn't know why an outage was being reported. 

Today ( 3/4/21 ) at  5pm, I got onto my home network to check if the outage was still present or had been fixed.  The MyAccount app indicated the outage was fixed!!   I ran speedtest and I am back to 24Mbps download speed. Come on . . .

I would like a detailed explanation of root cause for the mysterious outage that was suddenly reported and what was done to fix the outage on or before 2/21/2021 midnight  (probably 2/20/2021 evening) that ultimately fixed my network performance. 

I would like a detailed explanation of the root cause for the recent outage and what was done to fix it which appears to have reintroduced my network performance issue.