brintonh's profile

Visitor

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33 Messages

Sun, Mar 28, 2021 12:56 PM

Help! Can't figure out GB speed issue

Windows 10, LAN on MB (10/100/1000).  MoCA filter and splitter where cable enters house - one leg to video distribution box, second leg directly to my modem.  Had 200 MB plan and was getting around 180 MB.  Upgraded plan to 1200 MB and modem (Arris SB8200, DOCSIS 3.1), Cat 6 directly from desktop directly to modem port just to test - would "spike" speed to around 700 MB then immediately throttle down to 320 MB - 380 MB.  Reset and reprovisioned modem twice.  No change.  Had Comcast Tech out who checked speed at pole (1200 MB), speed at tap for house (1200 MB), speed at modem (1200 MB) with "excellent power levels" per Xfinity Tech.  Add SB8200 in the mix and speed drops to 320-380 MB.  Tech said "Speeds based on our equipment.  SB8200 might not hold full boot file. Try our Xfi modem."  Did that - same speeds.  Would spike to around 600 MB then drop back to 320-380 MB.  Hmmm, ok.  Try another gig speed modem.  Got a Netgear CM1200 yesterday.  Set up with Cat 6 direct from desktop to modem.  Testing wee hours of the AM and get a little better but not much - certainly not 1 GB. 

  Using speedtest.net app in W10 rather than browser test - Browser test is consistently 50-100 MB slower.  Modem reports:

Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 627000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Security Enabled BPI+
IP Provisioning Mode Honor MDD honorMdd(4)
 
Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 32 627000000 Hz 7.8 dBmV 41.2 dB 0 0
2 Locked QAM256 1 435000000 Hz 6.3 dBmV 40.6 dB 0 0
3 Locked QAM256 2 441000000 Hz 6.1 dBmV 40.5 dB 0 0
4 Locked QAM256 3 447000000 Hz 6.3 dBmV 40.5 dB 0 0
5 Locked QAM256 4 453000000 Hz 5.9 dBmV 40.5 dB 0 0
6 Locked QAM256 5 459000000 Hz 5.8 dBmV 40.5 dB 0 0
7 Locked QAM256 6 465000000 Hz 5.4 dBmV 40.4 dB 0 0
8 Locked QAM256 7 471000000 Hz 5.5 dBmV 40.4 dB 0 0
9 Locked QAM256 8 477000000 Hz 5.5 dBmV 40.4 dB 0 0
10 Locked QAM256 9 483000000 Hz 5.8 dBmV 40.5 dB 0 0
11 Locked QAM256 10 489000000 Hz 6.1 dBmV 40.5 dB 0 0
12 Locked QAM256 11 495000000 Hz 6.4 dBmV 40.4 dB 0 0
13 Locked QAM256 12 507000000 Hz 6.7 dBmV 40.5 dB 0 0
14 Locked QAM256 13 513000000 Hz 6.8 dBmV 40.6 dB 0 0
15 Locked QAM256 14 519000000 Hz 6.3 dBmV 40.6 dB 0 0
16 Locked QAM256 15 525000000 Hz 6.6 dBmV 40.8 dB 0 0
17 Locked QAM256 16 531000000 Hz 6.1 dBmV 40.8 dB 0 0
18 Locked QAM256 18 543000000 Hz 6.1 dBmV 40.7 dB 0 0
19 Locked QAM256 19 549000000 Hz 6.1 dBmV 40.7 dB 0 0
20 Locked QAM256 20 555000000 Hz 6.7 dBmV 40.9 dB 0 0
21 Locked QAM256 21 561000000 Hz 7.1 dBmV 40.9 dB 0 0
22 Locked QAM256 22 567000000 Hz 7.4 dBmV 41.1 dB 0 0
23 Locked QAM256 23 573000000 Hz 7.4 dBmV 40.9 dB 0 0
24 Locked QAM256 24 579000000 Hz 7 dBmV 40.9 dB 0 0
25 Locked QAM256 25 585000000 Hz 6.8 dBmV 40.8 dB 0 0
26 Locked QAM256 26 591000000 Hz 6.5 dBmV 41 dB 0 0
27 Locked QAM256 27 597000000 Hz 6.1 dBmV 41.1 dB 0 0
28 Locked QAM256 28 603000000 Hz 6.9 dBmV 41.2 dB 0 0
29 Locked QAM256 29 609000000 Hz 5.8 dBmV 41 dB 0 0
30 Locked QAM256 30 615000000 Hz 7 dBmV 41 dB 0 0
31 Locked QAM256 31 621000000 Hz 6.7 dBmV 41 dB 0 0
32 Not Locked Unknown 0 0 Hz 0.0 dBmV 0.0 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 35600000 Hz 43.5 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 29200000 Hz 44 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 44 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 16400000 Hz 44 dBmV
5 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
 
Downstream OFDM Channels
Channel Lock
Status
Modulation /
Profile ID
Channel
ID
Frequency Power SNR /
MER
Active Subcarrier
Number Range
Unerrored
Codewords
Correctable
Codewords
Uncorrectable
Codewords
1 Locked 0 ,1 ,2 ,3 33 678000000 Hz 7.7 dBmV 40.6 dB 1108 ~ 2987 107783651 105295721 0
2 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 0
 
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked 0 0 0 Hz 0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
 
Extended Upstream Transmit Power
Enable Extended Upstream Transmit Power
 
Current System Time:Sun Mar 28 06:41:00 2021
System Up Time:13:47:03

I'm at a loss to explain why I'm not getting the plan's reported speed.  I think I've isolated just about everything on the system except changing out LAN card in desktop but I'm thinking that's not it since I was briefly seeing 700-800MB before it dropped back down to 320-380MB.  Coax cable from tap on line to modem - check (good - no interference, no power drop, per Xfinity Tech).  Cat 6 - check (good, tried two different ones).  Modem - Check (three different modems, three different manufacturers).  Power levels in spec - check (Xfinity Tech confirmed). 

I'm at a loss to figure this out.  Hopefully someone will have an idea.  

Responses

Visitor

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33 Messages

2 m ago

@EG I see that you've been helpful to others with modem issues.  Can you take a look at this thread and give me your thoughts?

jlavaseur

Valued Contributor

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434 Messages

2 m ago

@brintonh is your computer any chance a Dell?

Visitor

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33 Messages

2 m ago

Frankenstein home built.  Box is ATX form factor from early 2000's that over the years has been upgraded with new power supply(s), motherboards and chips.  Current MB and chip are probably 5 years old

 

jlavaseur

Valued Contributor

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434 Messages

2 m ago

I’ll tell you something I sometimes do to help diagnose a particular difficult problem, it’s a little unconventional probably to most folks standards, anyway I have a ubuntu Linux install disk on a flash drive, so I boot this up, it boots up into memory, it gives a very nice functional desktop, no configuration needed in most cases, so your even online with your Ethernet port, so it gives the option to install or just try out, choose try out, so it already has Firefox installed, so I just navigate to my favorite speed test site, so this eliminates the windows operating system, different drivers etc, so I run a speed test and compare the results of the two, so in my case, with the 2.5 gig adapter I was originally getting slow speeds with win 10, with the Linux I was getting the 1400 - 1500 I posted before, the exact same hardware setup,  so that immediately ruled out my Comcast connection, modem and all my hardware I was using, so that told me it had something to do with win 10 I was using, but if you get the same speeds its probably a hardware issue, a simple test, but tells you what you need to know

Visitor

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33 Messages

2 m ago

BRAVO to jlavaseur for the suggestion on Unbuntu as a diagnostic tool!  Dowloaded, booted to Unbuntu and tested again, both going through router (Netgear R6700v3) and direct to modem.  Here's the results:

This is with the Motorola MB8611.  Clearly using Unbuntu and bypassing all the Windows 10 stuff (whatever that may be) get results close to 1GB.  Not quite there but I'd be happy to consistently get 800-850 Mbps down and 40 Mbps up in Windows 10.  At this point, not sure what else to sniff out in Windows to see if there's any way to match the Unbuntu speeds.  Open to suggestions.

Visitor

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1 Message

1 m ago

I have same issue with CM1200 Netgear. I have had techs reset modem, factory rest. A tech came in an also installed an Xfinity modem but speeds at pc were less than my CM1200. The tech was able to get 1200mbs on pole and at cable to modem. But those speeds could not be replicated on a pc, laptop, playstation by means of wifi or wired. My fluxuation in speeds changed 200mbs on testing but not over 500 at most. Any idea how to fix this? I upgraded from 200mb to 1200mb and nowhere near that speed.

Official Employee

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197 Messages

Hello, @user_8d300d. I see you are still seeing speed fluctuations even after a tech visit. We definitely want to get this sorted out. 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 on your forums page when signed in. Once there, you can search for "Xfinity Support" to compose your direct message. Please add your first and last name to help us locate your account. Let me know if you have any questions.

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