Forum Discussion

Diagnosis4995's avatar
Diagnosis4995
Joining in
14 hours ago

Hub 5 Stats and Levels - potential issues?

I’m looking for some advice and, if it warrants, an engineer visit, as my Hub 5 stats suggest an ongoing downstream DOCSIS 3.1 issue.

Background

I moved into this property about a year ago and brought my Virgin Media service with me from my previous house.

During renovation work, my builder offered to run some NX100 coax that I had previously used to extend Sky Q cabling. This was run under the floor and terminated with compression connectors, so I could locate my Hub 5 in an under-stairs cupboard. At the time, I didn’t think much of it.

My setup

  • Hub 5 in modem mode
  • OPNsense router with VLAN separation
  • 24 port managed switch
  • Ceiling mounted AP upstairs

Over time, I’ve had repeated issues with Sky Stream boxes, including slow channel loading and general instability, which led to multiple replacement boxes. That made me start looking more closely at the Virgin Media connection rather than the Sky hardware.

After checking the web and forums, I realised that extending the internal coax like this isn’t officially supported, as Virgin use specific cable and connectors to maintain signal quality and could be the reason for my sky issues.

Current cabling layout

The Virgin feed into the house is split externally.

  • One leg goes into the living room (this is the run that was extended internally using the NX100 cable).
  • Another leg runs around the front, side, and back of the house, then splits again to feed the two rear bedrooms.

To rule out the internal extension, I’ve now moved the Hub 5 upstairs and connected it directly to the original outlet there. I’m using Cat6a throughout the house, so router location isn’t an issue.

Since doing this, the connection does feel more stable. This might be placebo, but I’m seeing fewer post RS errors than when the hub was downstairs. That said, the downstream DOCSIS 3.1 channel still appears to be struggling, and upstream power levels are on the high side.

Hub details

Hub 5
Uptime: ~4.5 days

Issue observed

The DOCSIS 3.1 downstream OFDM channel is showing extremely high uncorrectable error counts over a relatively short uptime. DOCSIS 3.0 channels look broadly healthy by comparison.

Correct me if I'm wrong but from what I understand, this OFDM channel carries most of the traffic on a 500 Mb service, so this would explain intermittent performance issues even when speed tests sometimes look acceptable.

I’ve now removed the non-standard internal coax run from the equation, but the error rate suggests there may still be a signal or noise issue either on the external cabling, splitter configuration, or at the cabinet.

I’ve pasted my full downstream and upstream stats below.

Modem stats

3.0 Downstream channels

Channel  Frequency (Hz)  Power (dBmV)  SNR (dB)  Modulation  Channel ID
1   515000000  -5.4  38  QAM 256  48
2   139000000   0.6  39  QAM 256   1
3   163000000   0.8  38  QAM 256   4
4   171000000  -2.2  39  QAM 256   5
5   195000000  -3.2  39  QAM 256   8
6   203000000  -2.2  39  QAM 256   9
7   227000000  -2.9  39  QAM 256  12
8   235000000  -3.5  39  QAM 256  13
9   259000000  -3.9  39  QAM 256  16
10  267000000  -3.8  39  QAM 256  17
11  275000000  -3.1  39  QAM 256  18
12  283000000  -3.0  39  QAM 256  19
13  307000000  -3.2  39  QAM 256  22
14  315000000  -3.7  39  QAM 256  23
15  339000000  -4.2  39  QAM 256  26
16  347000000  -3.4  39  QAM 256  27
17  371000000  -3.6  39  QAM 256  30
18  379000000  -4.7  39  QAM 256  31
19  403000000  -5.3  38  QAM 256  34
20  411000000  -5.3  38  QAM 256  35
21  419000000  -4.7  38  QAM 256  36
22  427000000  -5.6  38  QAM 256  37
23  435000000  -5.6  38  QAM 256  38
24  443000000  -4.7  38  QAM 256  39
25  451000000  -5.7  38  QAM 256  40
26  459000000  -5.8  38  QAM 256  41
27  467000000  -5.2  38  QAM 256  42
28  475000000  -5.8  38  QAM 256  43
29  483000000  -5.6  38  QAM 256  44
30  491000000  -5.3  38  QAM 256  45
31  499000000  -5.9  38  QAM 256  46
32  507000000  -6.0  38  QAM 256  47
Channel  Locked  RxMER  Pre RS Errors  Post RS Errors
1   Locked  38  152336   216
2   Locked  39  1984722  246752
3   Locked  38  1503549  36867
4   Locked  39  2511397  309765
5   Locked  39  29896    3641
6   Locked  39  13719    1521
7   Locked  39  11052    1702
8   Locked  39  11813    914
9   Locked  39  7555     1156
10  Locked  39  7360     1034
11  Locked  39  9674     862
12  Locked  39  15196    1574
13  Locked  39  21596    2291
14  Locked  39  7633     848
15  Locked  39  2701     219
16  Locked  39  2544     350
17  Locked  39  4043     693
18  Locked  39  5688     240
19  Locked  38  22827    429
20  Locked  38  28284    544
21  Locked  38  34259    279
22  Locked  38  33851    217
23  Locked  38  33658    157
24  Locked  38  40376    430
25  Locked  38  47853    417
26  Locked  38  59408    344
27  Locked  38  72374    159
28  Locked  38  76705    249
29  Locked  38  89224    356
30  Locked  38  92496    342
31  Locked  38  100102   57
32  Locked  38  129376   111

3.1 Downstream channels

Channel  Width (MHz)  FFT  Active Subcarriers  Modulation  First Subcarrier (Hz)
159  94  4K  1840  QAM 4096  1108
Channel  Locked  RxMER  PLC Power (dBmV)  Corrected Errors  Uncorrectable Errors
159  Locked  0  -11.9  72588512  1870611403

3.0 Upstream channels

Channel  Frequency (Hz)  Power (dBmV)  Symbol Rate  Modulation  Channel ID
0  49600000  51.3  5120  QAM 64   9
1  43100000  50.0  5120  QAM 64  10
2  36600000  52.0  5120  QAM 64  11
3  30100000  51.0  5120  QAM 64  12
4  23600000  50.3  5120  QAM 64  13

3.1 Upstream channels

Channel  Width (MHz)  Power (dBmV)  FFT  Modulation
14  10  44.7  2K  QAM 256

I’d appreciate someone from Virgin Media taking a look and, if needed, arranging an engineer visit to properly check signal levels, splitters, and the DOCSIS 3.1 downstream path.

Broadband
Help
speed

9 Replies

  • Roger_Gooner's avatar
    Roger_Gooner
    Alessandro Volta
    5 hours ago

    You need a tech visit regardless of what's posted here. If you've removed the non-standard coax then there must be a splitter inside the omni box which should be replaced by a barrel connector. Any other splitters which are unused or have just one port in use need to be sorted out as well. Once the tech has dealt with your splitters and cleaned up your cabling by replacing your custom cables with official ones he can do his signal checks inside the house and, if necessary, at the cabinet. 

    • Diagnosis4995's avatar
      Diagnosis4995
      Joining in
      3 hours ago

      Ah cool thanks. Yes like i mentioned, there's definatly a two way splitter in the grey box outside, and then another two way splitter  is hidden under the floorboards upstairs somewhere which is feeding the two rooms upstairs. 

      With regards to a tech vist, do i need to call up is that something that will be picked up on this thread?

    • Diagnosis4995's avatar
      Diagnosis4995
      Joining in
      8 hours ago

      I don't have any long enough vm cables to test with as the wall box is quite far away from where all the ethernet cables in the house terminate under the stairs. I could plug the modem back in downstairs and send the stats if that helps?

      • Diagnosis4995's avatar
        Diagnosis4995
        Joining in
        8 hours ago

        so having plugged the modem back in understairs with the custom cable, these are the stats

        3.0 Downstream channels
        Channel    Frequency (Hz)    Power (dBmV)    SNR (dB)    Modulation    Channel ID
        1    515000000    1.2    40    QAM 256    48
        2    139000000    4.9    39    QAM 256    1
        3    163000000    4.3    39    QAM 256    4
        4    171000000    4.3    39    QAM 256    5
        5    195000000    4.1    40    QAM 256    8
        6    203000000    3.8    40    QAM 256    9
        7    227000000    3.4    40    QAM 256    12
        8    235000000    3.1    40    QAM 256    13
        9    259000000    2.4    40    QAM 256    16
        10    267000000    2.8    40    QAM 256    17
        11    275000000    2.8    40    QAM 256    18
        12    283000000    3.1    40    QAM 256    19
        13    307000000    3.3    40    QAM 256    22
        14    315000000    3.4    40    QAM 256    23
        15    339000000    3    40    QAM 256    26
        16    347000000    2.8    40    QAM 256    27
        17    371000000    2.5    40    QAM 256    30
        18    379000000    2.3    40    QAM 256    31
        19    403000000    1.5    40    QAM 256    34
        20    411000000    1.5    39    QAM 256    35
        21    419000000    1.4    40    QAM 256    36
        22    427000000    1.4    39    QAM 256    37
        23    435000000    1.5    40    QAM 256    38
        24    443000000    1.4    40    QAM 256    39
        25    451000000    1.5    40    QAM 256    40
        26    459000000    1.4    40    QAM 256    41
        27    467000000    1.2    40    QAM 256    42
        28    475000000    1.4    40    QAM 256    43
        29    483000000    1.3    40    QAM 256    44
        30    491000000    1.5    40    QAM 256    45
        31    499000000    1.4    40    QAM 256    46
        32    507000000    1.3    40    QAM 256    47

        3.0 Downstream channels
        Channel    Locked Status    RxMER (dB)    Pre RS Errors    Post RS Errors
        1    Locked    40    55    0
        2    Locked    39    0    0
        3    Locked    39    0    0
        4    Locked    39    0    0
        5    Locked    40    0    0
        6    Locked    40    0    0
        7    Locked    40    0    0
        8    Locked    40    0    0
        9    Locked    40    0    0
        10    Locked    40    0    0
        11    Locked    40    0    0
        12    Locked    40    0    0
        13    Locked    40    0    0
        14    Locked    40    1    0
        15    Locked    40    0    0
        16    Locked    40    0    0
        17    Locked    40    0    0
        18    Locked    40    0    0
        19    Locked    40    3    0
        20    Locked    39    6    0
        21    Locked    40    5    0
        22    Locked    39    8    0
        23    Locked    40    9    0
        24    Locked    40    12    0
        25    Locked    40    11    0
        26    Locked    40    23    0
        27    Locked    40    27    0
        28    Locked    40    16    0
        29    Locked    40    25    0
        30    Locked    40    26    0
        31    Locked    40    36    0
        32    Locked    40    40    0

        3.1 Downstream channels
        Channel    Channel Width (MHz)    FFT Type    Number of Active Subcarriers    Modulation (Active Profile)    First Active Subcarrier (Hz)
        159    94    4K    1840    QAM 4096    1108

        3.1 Downstream channels
        Channel ID    Locked Status    RxMER Data (dB)    PLC Power (dBmV)    Corrected errors (Active Profile)    Uncorrectable errors (Active Profile)
        159    Locked    0    -4.3    3502492    0


        3.0 Upstream channels
        Channel    Frequency (Hz)    Power (dBmV)    Symbol Rate (ksps)    Modulation    Channel ID
        0    49600000    45    5120    QAM 64    9
        1    43100000    44.5    5120    QAM 64    10
        2    36600000    44    5120    QAM 64    11
        3    30100000    44    5120    QAM 64    12
        4    23600000    43.5    5120    QAM 64    13

        3.0 Upstream channels
        Channel    Channel Type    T1 Timeouts    T2 Timeouts    T3 Timeouts    T4 Timeouts
        0    ATDMA    0    0    0    0
        1    ATDMA    0    0    0    0
        2    ATDMA    0    0    0    0
        3    ATDMA    0    0    0    0
        4    ATDMA    0    0    0    0

        3.1 Upstream channels
        Channel    Channel Width (MHz)    Power (dBmV)    FFT Type    Modulation
        14    10    39.0    2K    QAM 256

        3.1 Upstream channels
        Channel    Channel Type    Number of Active Subcarriers    First Active Subcarrier (Hz)    T3 Timeouts    T4 Timeouts
        14    OFDMA    200    74000000    0    0

        Hub 5 device information

        The information below shows current status of this Hub 5.
        Standard specification compliant
        :
        DOCSIS 3.1
        Hardware version
        :
        1.2
        Software version
        :
        LG-RDK_11.6.2-2410.1
        System up time
        :
        0day(s)0h:4m:47s
        Network access
        :
        Allowed

  • Client62's avatar
    Client62
    Alessandro Volta
    10 hours ago

    3.0 Downstream are just in the acceptable range but the spread of power levels is +0.6 to -6.0,
    that is a wide spread.  For us the 3.0 channels are within 1 dB & close to a power level of 0 dBmV.

    3.1. Downstream has a power level of -11.9 dBmV, this does need an engineer it is well below the preferred range of -7 to +7 dBmV, the low signal level is very likely the cause of the high number of Uncorrectable Errors.

    • Tudor's avatar
      Tudor
      Very Insightful Person
      9 hours ago

      Yep, those channel power needs to be rectified. From your description the upstairs cable contains two splitters. Now splitters, all of them, impose at lease 3dBm attenuation to the signal and that not good for you. How far are you from the street cabinet? You may need to be moved on a different tap in the cabinet. Any way you definitely need a technician’s visit.

      • Diagnosis4995's avatar
        Diagnosis4995
        Joining in
        9 hours ago

        There are 2 splitters yes, there's one in the grey box at the front of the house where the main cable comes in, as there's the cable coming into the living room termintating in a telewest broadband wall box, and then, there's the cable that goes around the house to back which then goes into, hidden somewhere upstairs, as i can't see it, another splitter which is feeding the 2 rooms. 

        If i remember correctly, when i did have the modem connected into the nx100 cable under the stairs, the signal levels where a lot higher, between 2db & 5db on the 3.0 downstream channels and between 43 & 45db on the upstream so the loss i would suspect is down to the old wiring, splitters and possibly the isolator in the upstairs bedrooms.