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Nathanc34's avatar
Nathanc34
New Contributor
4 years ago

OFDM Channel not locked - Downstream light consistently blinking now

Hi there, 

I hope someone can provide some insight on a problem I am having with my gigabit  internet service.   

Last week I was having intermittent service and the downstream light on my Netgear CM1200 modem was blinking.   From what I can tell this would mean that a channel or channels weren't locked.  I tried resetting the modem with no success.

I called cox support and they told me all they could do was look at the signal to my house which of course I was told it was "healthy".   Since they couldn't do much they had a technician come out the next day and have a look at everything.  Long story short nothing was noticed and I was told all my lines looked good. 

I shared my modem information with the tech and he did notice that I did have a few uncorrectable's on my downstream OFDM channel but he said it didn't look too bad. All the other channels looked fine.  After a few other discussions he did say that my modem might be going bad.  

While I didn't really want to buy a new modem since my modem was a little over a year old I went ahead and purchased the new Netgear CM2000 modem the same day and had it set up.      

Unfortunately Its been about 5 days with the new modem and I am still having the same issue.   My downstream light is blinking again so I decided to log into the modem and see if I could see anything different or wrong.   One thing I did notice was my downstream ODFM channel was no longer locked and not even showing a signal.   I called support again but I keep getting the same response that "everything looks fine".   I had to argue with them and explain it was not fine with them eventually agreeing to send someone out again tomorrow.    The downstream light has been blinking consistently now for over 16 hours. 

Would anyone have any idea what would be causing this or what I can do to remedy it?    Here is a copy of my modem status as of this post. 

Cable Connection
Cancel Apply
Frequency start Value
This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.
Starting Frequency
 
Startup Procedure
Procedure Status Comment
Acquire Downstream Channel 903000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Security Enabled BPI+
 
Downstream Bonded Channels (Partial Service)
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 21 903000000 Hz 1.1 dBmV 41.9 dB 0 0
2 Locked QAM256 1 783000000 Hz 4.3 dBmV 43.7 dB 0 0
3 Locked QAM256 2 789000000 Hz 4.3 dBmV 43.7 dB 0 0
4 Locked QAM256 3 795000000 Hz 4.0 dBmV 43.6 dB 0 0
5 Locked QAM256 4 801000000 Hz 4.1 dBmV 43.6 dB 0 0
6 Locked QAM256 5 807000000 Hz 3.9 dBmV 43.5 dB 0 0
7 Locked QAM256 6 813000000 Hz 3.8 dBmV 43.4 dB 0 0
8 Locked QAM256 7 819000000 Hz 3.8 dBmV 43.4 dB 0 0
9 Locked QAM256 8 825000000 Hz 3.5 dBmV 43.3 dB 0 0
10 Locked QAM256 9 831000000 Hz 3.3 dBmV 43.3 dB 0 0
11 Locked QAM256 10 837000000 Hz 3.2 dBmV 43.2 dB 0 0
12 Locked QAM256 11 843000000 Hz 2.8 dBmV 43.1 dB 0 0
13 Locked QAM256 12 849000000 Hz 2.5 dBmV 42.9 dB 0 0
14 Locked QAM256 13 855000000 Hz 2.5 dBmV 42.9 dB 0 0
15 Locked QAM256 14 861000000 Hz 2.1 dBmV 42.8 dB 0 0
16 Locked QAM256 15 867000000 Hz 2.0 dBmV 42.7 dB 0 0
17 Locked QAM256 16 873000000 Hz 1.9 dBmV 42.7 dB 0 0
18 Locked QAM256 17 879000000 Hz 1.7 dBmV 42.5 dB 0 0
19 Locked QAM256 18 885000000 Hz 1.6 dBmV 42.3 dB 0 0
20 Locked QAM256 19 891000000 Hz 1.4 dBmV 42.2 dB 0 0
21 Locked QAM256 20 897000000 Hz 1.4 dBmV 42.1 dB 0 0
22 Locked QAM256 22 909000000 Hz 1.3 dBmV 42.0 dB 0 0
23 Locked QAM256 23 915000000 Hz 1.0 dBmV 41.9 dB 0 0
24 Locked QAM256 24 921000000 Hz 0.8 dBmV 41.7 dB 0 0
25 Locked QAM256 25 927000000 Hz 1.0 dBmV 41.8 dB 0 0
26 Locked QAM256 26 933000000 Hz 0.8 dBmV 41.8 dB 0 0
27 Locked QAM256 27 939000000 Hz 0.8 dBmV 41.8 dB 0 0
28 Locked QAM256 28 945000000 Hz 0.9 dBmV 41.8 dB 0 0
29 Locked QAM256 29 951000000 Hz 0.7 dBmV 41.7 dB 0 0
30 Locked QAM256 30 957000000 Hz 0.4 dBmV 41.5 dB 0 0
31 Locked QAM256 31 963000000 Hz 0.4 dBmV 41.5 dB 0 0
32 Locked QAM256 32 969000000 Hz 0.1 dBmV 41.3 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 16900000 Hz 41.3 dBmV
2 Locked ATDMA 2 5120 23500000 Hz 42.3 dBmV
3 Locked ATDMA 3 5120 29900000 Hz 41.8 dBmV
4 Locked ATDMA 4 5120 36300000 Hz 41.8 dBmV
5 Not Locked Unknown 0 0 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 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 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 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

Thank you 

Nathan 

5 Replies

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  • Bruce's avatar
    Bruce
    Honored Contributor III
    4 years ago

    Netgear CM1200 is 32×8
    Downstream Light:  Blinking Green (Scanning for additional downstream channels)

    I don't know why the Downstream would be blinking because you have 32 locked channels.

    Your Upstream, however, only has 4 Bonded Channels.  I'd assume...due to gigabit...you should have 8.  Your Upstream Light should be blinking.

    dave9  would be the best source but I think the OFDM(A) channels are your overall circuits.  These circuits are then divided into separate channels:  32 and 4.  Therefore the overall circuits wouldn't be individually locked.  I could be wrong and sure I am.

    I guess a good question:  why don't you have 8 Upstream channels?

    • Nathanc34's avatar
      Nathanc34
      New Contributor
      4 years ago

      Hi Bruce, I appreciate the response.

      I am not sure why I don't have 8 upload channels locked but at this point Cox has decided that now my brand new modem is also the "Issue".   The issue has been consistent through my Netgear CM1200 as well as the Netgear CM2000 modem I just purchased two weeks ago.    The concerning part for me is they installed one cox modem and it actually wouldn't lock the downstream channels either.  They said their modem must have an issue as well.   So now we are on a forth modem(another cox modem) to see if they can pinpoint the issue.    After provisioning it did lose connection but I was told it was probably upgrading the firmware so that is why it was down. 

      I hate to sound negative but I find it very hard to believe that 3 out of 4 different modems(including one of cox's) are the issue and not something with the signal.  

      I now seem to have the ODFM channel locked as of this morning (after 12 hours) but there the SNR and power levels don't have any readings.  Shouldn't there be some kind of signal information?

      Any thoughts on this? This is from cox modem model # CGM4140COM

      Downstream
      		 Channel Bonding Value
      Index
      13
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      14
      15
      16
      33
      34
      35
      36
      37
      38
      39
      40
      41
      42
      43
      44
      45
      46
      47
      48
      159
      Lock Status
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Frequency
      855 MHz
      783 MHz
      789 MHz
      795 MHz
      801 MHz
      807 MHz
      813 MHz
      819 MHz
      825 MHz
      831 MHz
      837 MHz
      843 MHz
      849 MHz
      861 MHz
      867 MHz
      873 MHz
      357 MHz
      363 MHz
      369 MHz
      375 MHz
      381 MHz
      387 MHz
      393 MHz
      399 MHz
      405 MHz
      411 MHz
      417 MHz
      423 MHz
      429 MHz
      435 MHz
      441 MHz
      447 MHz
      300000000
      SNR
      42.3 dB
      43.5 dB
      43.4 dB
      43.4 dB
      43.3 dB
      43.1 dB
      43.3 dB
      43.1 dB
      42.9 dB
      42.9 dB
      42.7 dB
      42.7 dB
      42.4 dB
      42.2 dB
      42.1 dB
      41.7 dB
      45.0 dB
      45.4 dB
      45.2 dB
      45.2 dB
      45.3 dB
      45.3 dB
      45.4 dB
      45.4 dB
      45.4 dB
      45.3 dB
      45.3 dB
      45.2 dB
      45.2 dB
      45.2 dB
      45.1 dB
      45.2 dB
      NA
      Power Level
      2.2 dBmV
      3.8 dBmV
      3.7 dBmV
      3.7 dBmV
      3.7 dBmV
      3.5 dBmV
      3.7 dBmV
      3.5 dBmV
      3.3 dBmV
      3.3 dBmV
      2.8 dBmV
      2.7 dBmV
      2.4 dBmV
      2.0 dBmV
      1.9 dBmV
      1.5 dBmV
      4.1 dBmV
      4.1 dBmV
      4.2 dBmV
      4.1 dBmV
      4.3 dBmV
      4.3 dBmV
      4.3 dBmV
      4.3 dBmV
      4.4 dBmV
      4.5 dBmV
      4.5 dBmV
      4.6 dBmV
      4.5 dBmV
      4.5 dBmV
      4.4 dBmV
      4.2 dBmV
      NA
      Modulation
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      256 QAM
      OFDM
      Upstream
      		 Channel Bonding Value
      Index
      1
      2
      3
      4
      5
      6
      7
      8
      Lock Status
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Locked
      Frequency
      16 MHz
      23 MHz
      29 MHz
      36 MHz
      60 MHz
      67 MHz
      74 MHz
      81 MHz
      Symbol Rate
      5120
      5120
      5120
      5120
      5120
      5120
      5120
      5120
      Power Level
      40.5 dBmV
      41.5 dBmV
      41.0 dBmV
      41.0 dBmV
      41.8 dBmV
      42.5 dBmV
      42.5 dBmV
      43.0 dBmV
      Modulation
      QAM
      QAM
      QAM
      QAM
      QAM
      QAM
      QAM
      QAM
      Channel Type
      ATDMA
      ATDMA
      ATDMA
      ATDMA
      ATDMA
      ATDMA
      ATDMA
      ATDMA

      CM Error Codewords
      Index
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      27
      28
      29
      30
      31
      32
      33
      Unerrored Codewords
      2985830488
      2394402663
      2394409589
      2394416138
      2394423578
      2394430285
      2394437436
      2394445207
      2394453297
      2394460406
      2394467767
      2394474395
      2394481221
      2394487381
      2394494060
      2394499908
      2394505276
      2394512736
      2394519020
      2394525227
      2394531941
      2394538605
      2394545097
      2394551929
      2394557930
      2394566396
      2394573800
      2394581273
      2394588059
      2394595046
      2394600590
      2394604125
      2985830488
      Correctable Codewords
      268983428
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      268983428
      Uncorrectable Codewords
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      0
      • MariaL's avatar
        MariaL
        Moderator
        4 years ago
        Hi Nathanc34,

        We can certainly investigate this issue for you. Please email our team at cox.help@cox.com with this post, your full name, and complete address. You can also reach out to us on Twitter and Facebook through the links below:

        www.facebook.com/.../

        https://twitter.com/CoxHelp

        Maria
        Cox Support Forum Moderator
    • Dave9's avatar
      Dave9
      Contributor III
      4 years ago

      As far as I know, very few areas have 8 upstream channels. Most have 4, and a few have 5 (really more like 4 1/2) due to congestion. Gigablast only supports up to 35 Mbit upstream so 4 channels is more than enough for that. As you pointed out it's odd that the OFDMA channel isn't locked since I think all of Cox is on DOCSIS 3.1 now. That's something a tech would need to investigate. As mentioned, it could be caused by noise issues in the 300 MHz band used by OFDMA.

      Moral of the story is that Cox always blames the modem because it's a quick way to get customers off the phone and keep call times down. And very rarely a modem does break down. But it's almost never the modem. It's a good idea to keep up with new technology and upgrade your modem every few years but most of the time when Cox blames the modem they're just plain wrong.