S

Visitor

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10 Messages

Tue, Sep 28, 2021 12:07 AM

Intermittent performance problems

Hi,

I've been having intermittent performance problems where every few days download throughput drops from the plan rate of 100Mbps (sometimes even as high as 117Mbps) to about 33Mbps as measured by speedtest.xfinity.com from a system adjacent to the modem (Arris SBG8300). Other systems on the same network see a performance drop as well. The modem does not report any problems, nor does Xfinity, but a reboot fixes it for a few days.

Is there anyway to distinguish between a problem I'm responsible for (modem, in-house cabling, etc.) and something Xfinity is responsible for?

Thanks,

Skylar

Accepted Solution

EG

Expert

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89.9K Messages

21 d ago

If there is nothing that can be done to improve the connection, then as stated,  you might want to get a tech out to investigate this issue.

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home.


Good luck !

 

EG

Expert

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89.9K Messages

1 m ago

Are these WiFi connections ? If so, for a test, does a computer / device that is hardwired directly to the 8300 with an ethernet cable have the same problem ?


With this test, we are trying to isolate this from being either a WiFi-only problem or a problem with the general connection to the Comcast system which would of course affect both. It's a good first step of troubleshooting before proceeding any further.

Visitor

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10 Messages

1 m ago

Good call, these tests were on wifi. I do have a cabled system plugged in, though I'm not experiencing any performance problems now. I just ran the speedtest though to get a baseline, confirmed to be at 100Mbps right now.

Skylar

Official Employee

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241 Messages

@skylar42, thank you for running a hardwired speed test. As @EG pointed out, this is an excellent first step for troubleshooting any speed issues. You can also troubleshoot your internet connection right from our Xfinity My Account app when these issues arise. 

 

That being said, intermittent issues can be hard to pin down. How have your services been working since your last comment yesterday?

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Visitor

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10 Messages

Sorry for the delay, somehow missed this reply. Things were fine until today, but today we started having outright connection failures (green modem light went blue, then had to reboot the modem). There was one this morning, and then another one in the evening about 30 minutes ago. After the reboot, things are fine, including a speed test. There's nothing in the system or event logs on the modem to indicate a problem.

Let me know if there's any other information that would be useful.

Thanks,

Skylar

EG

Expert

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89.9K Messages

22 d ago

What do the modem's signal stats look like ? 


Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

Visitor

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10 Messages

@EG Here's what I've got for downstream:

Index Frequency (Hz) Power Level (dBmV) SNR (dB)
1 645000000 -10.299999 36.609653
2 651000000 -10.599998 36.609653
3 657000000 -10 36.38689
4 663000000 -10.299999 35.779911
5 669000000 -10.299999 36.38689
6 675000000 -9.900002 36.609653
7 681000000 -10.200001 36.609653
8 687000000 -9.599998 37.355988
9 693000000 -9.900002 37.636276
10 699000000 -10 37.355988
11 705000000 -10.200001 36.38689
12 711000000 -10 35.779911
13 717000000 -10.5 35.779911
14 723000000 -10.299999 36.609653
15 729000000 -10.400002 37.092701
16 735000000 -10.400002 35.779911
17 741000000 -10 35.779911
18 747000000 -10.299999 35.595078
19 753000000 -10.099998 35.083549
20 759000000 -10.099998 36.38689
21 765000000 -10.5 35.972961
22 771000000 -10.400002 36.38689
23 777000000 -10 37.355988
24 783000000 -9.799999 37.636276
25 789000000 -9.400002 37.636276
26 795000000 -9.5 37.636276
27 801000000 -9.599998 37.636276
28 807000000 -9.799999 37.636276
29 813000000 -10.200001 37.355988
30 819000000 -10 37.355988
31 825000000 -10.099998 37.636276
32 831000000 -10.299999 37.355988

and for upstream (no signal:noise ratio available though):

Index Frequency (Hz) Power Level (dBmV)
9 10400000 44.0103
14 40400000 46.5103
13 35600000 46.520599
12 29200000 45.520599
11 22800000 45.020599
10 16400000

45.020599

Let me know if you need any other information, or if there's somewhere else I should look for the upstream data.

Thanks!

Skylar

EG

Expert

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89.9K Messages

22 d ago

The downstream power is too low /out of spec. And some of the SNR's are on the low side. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1000 MHz, bi-directional, and no gold colored garbage from Radio Shack, Home Depot, Target, etc. Splitters should be swapped with known to be good / new ones to test.

Also check the coax cable for any damage such as cuts, nicks, kinks, sharp bends, etc.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.


Good luck with it !

Visitor

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10 Messages

Thanks, @EG ! We do have some splitters, though I'll have to see if they're actually connected (just moved into this place two months ago). Out of curiosity, what's the target for power level and SNR? I've found this doc from Arris that suggests with QAM256 and DPL between -15dBmV and -6dBmV (looks like what we have), we should have SNR of at least 33, so we're at the low-end but still in-spec. In any case, though, I'd like to make sure that whatever changes we make actually are an improvement. :)

https://arris.secure.force.com/consumers/articles/General_FAQs/SB8200-Cable-Signal-Levels/?l=en_US&fs=RelatedArticle

Skylar

EG

Expert

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89.9K Messages

22 d ago

It's the Comcast plant / engineering specs that matter ! These are from the pinned "Troubleshooting Tips" post at the top of this board;

 

Specification      Min             Max
Downstream Power Level    
Cable Modems -10dBmV +10dBmV
Gateways and EMTAs -7dBmV +7dBmV
Downstream Signal to Noise Ratio 35dB -
Upstream Power Level +35dBmV +50dBmV
Upstream Signal to Noise Ratio 31dB -
Upstream Receive Power -2dBmV +2dBmV

 

Visitor

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10 Messages

Thanks again, @EG ! Knew I should have checked the pinned posts first...

Did some cable tracing, looks like we have a single two-way splitter on the network path (Extreme Broadband, 5-1002Mz, -3.5dbm loss) that still appears to be in good condition. The cable ends I can see appear to be in good condition, though blew some dust off. That leaves the cable from the modem to the wall, which is of unknown providence. I'll be replacing that next, hopefully that clears things up.

Skylar

Visitor

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10 Messages

Unfortunately, it looks like all of our work has made things worse than before, now have some downstream channels that have SNR levels as low as 31dB. Hopefully the new cable fixes things...

Skylar

Official Employee

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270 Messages

Hello @skylar42, it is truly unfortunate to hear things have gotten worse. Could you please send our team a private message with your full name and full address? Our team would like to take a further look at the appointment for your new cable.

To send a "Peer to peer" ("Private") message:
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• Click the "Peer to peer chat" icon
• Click the "New message" (pencil and paper) icon
• Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line
• Type your message in the text area near the bottom of the window
• Press Enter to send it

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick
EG

Expert

 • 

89.9K Messages

@XfinityAldrik

Did you see their update ? 

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Please mark an Accepted Answer!tick

Visitor

 • 

10 Messages

9 d ago

I just wanted to post an update, and fortunately a happy resolution. As you suspected, the problem was the cable between the modem and the wall. Moral of the story is, don't trust the 15 year old cable that came out of a random box after moving. New cable is much better with SNR and power level numbers all within spec.

Skylar

EG

Expert

 • 

89.9K Messages

8 d ago

@skylar42 

Thanks for circling back ! For curiosity, would you please post what the stats look like now ?

Visitor

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10 Messages

@EG Absolutely, here's the latest numbers:

Downstream Index Frequency (Hz) Power Level (dBmV) SNR (dB) Modulation Lock Status
41 885000000 -12.700001 35.779911 QAM256 Locked
33 837000000 -10.599998 37.636276 QAM256 Locked
34 843000000 -11.599998 37.355988 QAM256 Locked
35 849000000 -12.400002 36.609653 QAM256 Locked
36 855000000 -12.299999 36.38689 QAM256 Locked
37 861000000 -12.200001 36.609653 QAM256 Locked
38 867000000 -11.799999 36.38689 QAM256 Locked
39 873000000 -12.299999 35.779911 QAM256 Locked
40 879000000 -12.299999 35.779911 QAM256 Locked
42 891000000 -12.599998 35.779911 QAM256 Locked
43 897000000 -11.5 36.38689 QAM256 Locked
44 903000000 -11 36.609653 QAM256 Locked
13 717000000 -10.299999 37.636276 QAM256 Locked
14 723000000 -10 38.605377 QAM256 Locked
15 729000000 -10.099998 38.605377 QAM256 Locked
16 735000000 -9.900002 37.636276 QAM256 Locked
17 741000000 -9.200001 38.605377 QAM256 Locked
18 747000000 -9.599998 37.636276 QAM256 Locked
19 753000000 -9.700001 38.983261 QAM256 Locked
20 759000000 -9.900002 38.605377 QAM256 Locked
21 765000000 -10.299999 37.355988 QAM256 Locked
22 771000000 -10.200001 37.636276 QAM256 Locked
23 777000000 -9.799999 37.636276 QAM256 Locked
24 783000000 -9.299999 38.605377 QAM256 Locked
25 789000000 -8.700001 38.983261 QAM256 Locked
26 795000000 -9.099998 38.605377 QAM256 Locked
27 801000000 -10 38.605377 QAM256 Locked
28 807000000 -10.599998 37.636276 QAM256 Locked
29 813000000 -10.700001 37.636276 QAM256 Locked
30 819000000 -10 38.605377 QAM256 Locked
31 825000000 -9.900002 38.605377 QAM256 Locked
32 831000000 -10 37.636276 QAM256

Locked

Upstream Index Frequency (Hz) Power Level (dBmV) Channel Type Symbol Rate (KSym/sec) Modulation Lock Status
9 10400000 43.5103 US_TYPE_STDMA 2560 KSym/sec 16QAM ACTIVE
14 40400000 45.7603 US_TYPE_STDMA 2560 KSym/sec 64QAM ACTIVE
13 35600000 45.270599 US_TYPE_STDMA 5120 KSym/sec 64QAM ACTIVE
12 29200000 45.270599 US_TYPE_STDMA 5120 KSym/sec 64QAM ACTIVE
11 22800000 44.770599 US_TYPE_STDMA 5120 KSym/sec 64QAM ACTIVE
10 16400000 44.270599 US_TYPE_STDMA 5120 KSym/sec 64QAM ACTIVE

Minimum downstream SNR is now 35 (up from 29, sometimes even less). Not as good as it could be, but connection is solid now.

Skylar

EG

Expert

 • 

89.9K Messages

7 d ago

@skylar42 

More needs to be done.... Most of the downstreams are still too low / out of spec. There's no wiggle room. You may want to get a tech out to investigate / correct the problem. Good luck !

Visitor

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10 Messages

4 d ago

Yeah, still not perfect though performance is much more consistent/stable. If it gives us more trouble we'll get a tech out though. Thanks for the help and suggestions!

Skylar

EG

Expert

 • 

89.9K Messages

4 d ago

Hope things hold up for you ! Good luck !

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