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Monday, March 4th, 2024 10:36 PM

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SB8200 Constant internet performance degradation.

I am paying for 1000Mbps/20Mbps, but can barely reach 300Mbps download following clean reboot of the modem. While I don't expect the SB8200 to reach true gigabit speed due to the DOCSIS version, I expect it to be much higher than 1/3 of the advertised download speed.  It is still listed as a supported Xfinity Modem with 'Wired Download Speed: Up to 957 Mbps'.  

I am plugged in directly to the modem to rule out any other network elements in my setup.  SNR and channel information following a fresh reboot are below.  Please help with next steps.  

Information
Standard Specification Compliant Docsis 3.1
Hardware Version 7
Software Version AB01.02.053.05_051921_193.0A.NSH
Cable Modem MAC Address [Edited: "Personal Information"]
Serial Number [Edited: "Personal Information"]

Status
Up Time 0 days 00h:35m:34s.00

Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 507000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK
Security Enabled BPI+
DOCSIS Network Access Enabled Allowed

Downstream Bonded Channels
Channel ID Lock Status Modulation Frequency Power SNR/MER Corrected Uncorrectables
9 Locked QAM256 507000000 Hz -0.4 dBmV 41.5 dB 0 0
6 Locked QAM256 489000000 Hz 1.9 dBmV 41.9 dB 0 0
7 Locked QAM256 495000000 Hz -0.6 dBmV 41.4 dB 0 0
8 Locked QAM256 501000000 Hz -5.3 dBmV 40.0 dB 0 0
10 Locked QAM256 513000000 Hz 1.0 dBmV 41.6 dB 0 0
11 Locked QAM256 519000000 Hz -0.7 dBmV 41.3 dB 0 0
12 Locked QAM256 525000000 Hz -4.8 dBmV 39.9 dB 0 0
13 Locked QAM256 531000000 Hz -1.7 dBmV 40.8 dB 0 0
14 Locked QAM256 537000000 Hz 1.4 dBmV 41.6 dB 0 0
15 Locked QAM256 543000000 Hz -0.4 dBmV 41.1 dB 0 0
16 Locked QAM256 549000000 Hz -4.3 dBmV 39.3 dB 0 0
17 Locked QAM256 555000000 Hz -4.4 dBmV 39.1 dB 0 0
18 Locked QAM256 561000000 Hz 1.2 dBmV 41.4 dB 0 0
19 Locked QAM256 567000000 Hz 1.3 dBmV 41.3 dB 0 0
20 Locked QAM256 573000000 Hz -2.2 dBmV 40.0 dB 0 0
21 Locked QAM256 579000000 Hz -6.4 dBmV 38.6 dB 0 0
22 Locked QAM256 585000000 Hz -0.5 dBmV 40.9 dB 0 0
23 Locked QAM256 591000000 Hz 1.1 dBmV 41.2 dB 0 0
24 Locked QAM256 597000000 Hz -1.0 dBmV 40.6 dB 0 0
25 Locked QAM256 603000000 Hz -5.6 dBmV 38.9 dB 0 0
26 Locked QAM256 609000000 Hz -0.9 dBmV 40.5 dB 0 0
27 Locked QAM256 615000000 Hz 1.6 dBmV 41.0 dB 0 0
28 Locked QAM256 621000000 Hz 0.0 dBmV 40.7 dB 0 0
29 Locked QAM256 627000000 Hz -4.5 dBmV 38.9 dB 0 0
30 Locked QAM256 633000000 Hz -2.8 dBmV 39.7 dB 0 0
31 Locked QAM256 639000000 Hz 2.1 dBmV 41.0 dB 0 0
32 Locked QAM256 645000000 Hz 1.6 dBmV 40.8 dB 0 0
33 Locked QAM256 651000000 Hz -2.7 dBmV 39.7 dB 0 0
34 Locked QAM256 657000000 Hz -6.5 dBmV 38.4 dB 0 0
35 Locked QAM256 663000000 Hz -0.5 dBmV 40.6 dB 0 0
36 Locked QAM256 669000000 Hz 0.4 dBmV 40.7 dB 0 0
37 Locked Other 690000000 Hz 0.0 dBmV 36.2 dB 77531315 0


Upstream Bonded Channels
Channel Channel ID Lock Status US Channel Type Frequency Width Power
1 1 Locked SC-QAM Upstream 35600000 Hz 6400000 Hz 50.0 dBmV
2 2 Locked SC-QAM Upstream 29200000 Hz 6400000 Hz 56.0 dBmV
3 3 Locked SC-QAM Upstream 22800000 Hz 6400000 Hz 51.0 dBmV
4 4 Locked SC-QAM Upstream 16400000 Hz 6400000 Hz 58.0 dBmV
5 5 Locked SC-QAM Upstream 39600000 Hz 1600000 Hz 52.0 dBmV


Expert

 • 

110.2K Messages

1 year ago

This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless. 

The upstream power is too high / out of spec, and it may be intermittently fluctuating even farther out. 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 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 5-1002 MHz, bi-directional, and no gold colored garbage from Home Depot, Target, Wal-Mart, 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, abrasions, 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 !

Official Employee

 • 

2.2K Messages

1 year ago

Hi, @user_xc0q8t. Thank you for reaching out and creating a detailed post outlining the issues you see. As @EG mentioned there are a few things we needed to review on our end. 

I ask that you reach out privately, so we can cover the details of your account. You can start by clicking the chat icon located in the top right corner of your forums page when signed in. Once there, you can direct your messages to "Xfinity Support." Please add your full name and service address to help us locate your account. Let me know if you have any questions.

Expert

 • 

110.2K Messages

1 year ago

@user_xc0q8t 

Did you get a chance to see if any of those tips apply ? Please update your topic right here on these public help forums. Thank you.

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