Possible Problem : Excessive Downstream/Upstream Power Levels

[EducatedPork]

Hi,

Around a month ago the area I live in was subjected to massive lightning strikes that took out some equipment in the cabinet near to my home and also a load of equipment in my home (and many others). Anyway, the engineer changed which bit of equipment I was connected to in the cabinet pending repair/replacement of the stuff that had been fried in the cabinet. During this I was also migrated to a Hub 5 as part of a move to 1Gbit broadband.

In the last few weeks I’ve noticed a few stalls in my internet access - i checked the logs/levels for the Hub 5 to see if anything stood out. I’m concerned that the power levels may be too high and as such contributing to the entries I’m seeing in the logs.. so I thought I’d post up my details here in the hope someone (from VM?) could comment on them.

I’m located around 15-20 metres from the cabinet, and as I mentioned I’ve a Hub 5. There’s a powered splitter (amplifier?) of some kind on the cable coming into the house, with one of the splitter outputs going to the Hub 5 and the other going to my TV 360 box. Maybe that amplification isn’t needed anymore if I’ve been moved to another connection in the cabinet with different attenuation properties? 

Thanks,
Dean

3.0 Downstream channels

Channel Frequency (Hz) Power (dBmV) SNR (dB) Modulation Channel ID

1 331000000 15.6 42 QAM 256 25

2 147000000 13.4 40 QAM 256 2

3 155000000 13.2 39 QAM 256 3

4 163000000 13.1 40 QAM 256 4

5 171000000 13.1 41 QAM 256 5

6 179000000 13.2 41 QAM 256 6

7 187000000 13.4 41 QAM 256 7

8 195000000 14 41 QAM 256 8

9 203000000 14 41 QAM 256 9

10 211000000 14.2 42 QAM 256 10

11 219000000 14.2 41 QAM 256 11

12 227000000 14.2 42 QAM 256 12

13 235000000 14.4 42 QAM 256 13

14 243000000 14.5 42 QAM 256 14

15 251000000 14.3 42 QAM 256 15

16 259000000 14.4 42 QAM 256 16

17 267000000 14.4 42 QAM 256 17

18 275000000 14.3 42 QAM 256 18

19 283000000 14.3 42 QAM 256 19

20 291000000 14.1 42 QAM 256 20

21 299000000 13.9 42 QAM 256 21

22 307000000 14.3 42 QAM 256 22

23 315000000 14.8 42 QAM 256 23

24 323000000 15.3 42 QAM 256 24

25 339000000 15.9 42 QAM 256 26

26 347000000 16.2 43 QAM 256 27

27 355000000 16.4 43 QAM 256 28

28 363000000 16.6 43 QAM 256 29

29 371000000 16.8 43 QAM 256 30

30 379000000 16.8 43 QAM 256 31

31 387000000 17 43 QAM 256 32

3.0 Downstream channels

Channel Locked Status RxMER (dB) Pre RS Errors Post RS Errors

1 Locked 42 20 0

2 Locked 40 82 0

3 Locked 39 76 0

4 Locked 40 91 0

5 Locked 41 51 0

6 Locked 41 43 0

7 Locked 41 40 0

8 Locked 41 24 0

9 Locked 41 30 0

10 Locked 42 20 0

11 Locked 41 23 0

12 Locked 42 29 0

13 Locked 42 22 0

14 Locked 42 25 0

15 Locked 42 24 0

16 Locked 42 23 0

17 Locked 42 39 0

18 Locked 42 24 0

19 Locked 42 33 0

20 Locked 42 50 0

21 Locked 42 63 0

22 Locked 42 57 0

23 Locked 42 39 0

24 Locked 42 19 0

25 Locked 42 28 0

26 Locked 43 9 0

27 Locked 43 15 0

28 Locked 43 13 0

29 Locked 43 13 0

30 Locked 43 11 0

31 Locked 43 16 0

3.1 Downstream channels

Channel ID Locked Status RxMER Data (dB) PLC Power (dBmV) Corrected errors (Active Profile) Uncorrectable errors (Active Profile)

33 Locked 39 18.2 502735537 779414

3.0 Upstream channels

Channel Frequency (Hz) Power (dBmV) Symbol Rate (ksps) Modulation Channel ID

0 49600000 47.3 5120 QAM 64 1

1 43100000 47 5120 QAM 64 2

2 36600000 47 5120 QAM 64 3

3 30100000 47 5120 QAM 64 4

4 23600000 47.3 5120 QAM 64 5

3.1 Upstream channels

Channel Channel Width (MHz) Power (dBmV) FFT Type Modulation

6 10.4 43.0 2K QAM 256

Network Log

Time	Priority	Description
10-05-2024 15:58:24	notice	US profile assignment change. US Chan ID: 6; Previous Profile: 11 13; New Profile: 12 13.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
10-05-2024 15:58:20	notice	US profile assignment change. US Chan ID: 6; Previous Profile: 12 13; New Profile: 11 13.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
10-05-2024 15:53:17	notice	US profile assignment change. US Chan ID: 6; Previous Profile: 11 13; New Profile: 12 13.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;
10-05-2024 15:52:33	notice	US profile assignment change. US Chan ID: 6; Previous Profile: 12 13; New Profile: 11 13.;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.1;

[RT123]

Forum team replies can take a few days but I can confirm that the downstream power levels are high (should be less than 10dBmV) so it does need investigating by Virgin

[jpeg1]

Upstream is OK, but a 10dB forward path attenuator would be a good idea. 

[Sephiroth]

The "powered splitter" thing is a passive splitter with no amplification; on the contrary, it knocks some of the power off what reaches the Hub. You can't do without it if you want both TV and Hub to work.

In ordinary circumstances, being so close to the cabinet, your circuit would be placed on a tap point with high attenuation (https://community.virginmedia.com/t5/Networking-and-WiFi/POWER-LEVELS-amp-SNR-A-TECHNICAL-PRIMER-upd...) but clearly this hasn't occurred.  The tech, when he/she comes, needs to deal with that.

Your high Docsis 3.1 downstream channel power, at 18.9 dBmv is the likely cause of the data corruption on that channel such that important keep-alive traffic can't be read and thus cannot be responded to.

Btw, it seems odd to me that the upstream power is at 44 dbMv; I would have expected it to be around 32 dBmv; it could be the post-lightning state of other components in the cabinet that would account for the power level.

Looks to me that VM have made a temporary kludge.

[Joseph_B]

Hey @EducatedPork,

Welcome back to the Community Forums and thanks for the post.

Sorry to see you have been having this issue with your Hub, looking into this you would benefit from having a technician sent so that we can look into fixing this through for you, for me to raise this through I will need to confirm some information from you via private message.

Joe

[IPFreely]

Sounds a lot like said splitter is indeed powered. 

If I recall they install a Technetix HDU-200.

https://emea.technetix.com/product/premises-amplifier-2-outputs-unity-gain/

Supposed to amplify in both directions but seems far more keen on downstream. There's a model that only amplifies downstream, too. Older version which might explain things. 

[Sephiroth]

Ah yes - I’d forgotten about that possibility. 

[EducatedPork]

Hi,

Just as a follow-up on this, Joseph_B sorted out an engineer visit for me - he fitted a 15db attenuator to the cable at the point that it goes into the powered splitter.

3.0 Downstream power levels are now between -1.7 and 1.5dBmv, with SNR of between 39 and 42 - which looks a lot more reasonable.

3.1 Downstream power level is 2.9dBmV

Upstream power level remains around 43dBmv. He said that was well within the acceptable range (it certainly seems in the range described in Sephiroth's "power levels & SNR" technical posts here).

Everything still seems to be working - so thanks to everyone for the help here!

Cheers,
Dean

[Gareth_L · Accepted solution]

Hello Dean.

Thanks for your update.

Glad to hear the service is now working as it should be.

We're always here if you need anything else.

Have a good day.

Gareth_L