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Author Topic: Downstream line attenuation difference on modem routers  (Read 989 times)

Alex Atkin UK

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Re: Downstream line attenuation difference on modem routers
« Reply #15 on: November 13, 2020, 08:36:32 PM »

The physical line characteristics haven't changed - it's still the same length. Just that the Hub One is generally not a good modem (from experience). Attenuation readings can be ignored for the most part, as long as the line is performing as it should. Only worry would be if one modem was showing a very high reading, or if all were. But nothing to see here. Just put one of the modems on and leave it alone.

I'm not sure its fair to say the Hub One in generally not a good modem.  Its not a good router, but the modem depends entirely on your line.

Certainly with OpenWRT on the right line, I think the uptime speaks for itself. (well this is my HH5a but basically the same)

Code: [Select]
Chipset: Lantiq™ XWAY™ VRX268
Firmware Version: 5.8.1.8.1.6
API Version: 4.17.18.6
MEI Version: 1.5.17.6
Power Management Mode: L0 - Synchronized
Line State: UP [0x801: showtime_tc_sync]

Line Uptime: 71d 1h 17m 6s

Attain Data Rate: 79.396 Mb/s / 24.529 Mb/s
Actual Data Rate: 67.000 Mb/s / 20.000 Mb/s
Impulse Noise Prot: 0.0 sym / 0.0 sym
Interleave Delay: 0.0 ms / 0.0 ms
NFEC: 255 / 255
RFEC: 16 / 16
LSYMB: 17979 / 5410
Interleave Depth: 1 / 1
Interleave Block: 255 / 255
LPATH: 0 / 0
Line Attenuation: 12.9dB / 15.9dB
Signal Attenuation: 12.9dB / 15.7dB
Noise Margin: 5.7dB / 7.8dB
Transmit power: 13.7dBm / 5.3dBm
FECS: 7842198 / 59521
ES: 3838 / 60207
SES: 0 / 18
LOSS: 5 / 0
UAS: 2147 / 2147
HEC: 0 / 0
CRC_P: 0 / 0
CRCP_P: 0 / 0
15m Code Violations: 0 / 1
15m FEC Errors: 2071 / 2
1d Code Violations: 51 / 90
1d FEC Errors: 173847 / 458
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Weaver

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Re: Downstream line attenuation difference on modem routers
« Reply #16 on: November 13, 2020, 09:05:41 PM »

I am assuming that the attenuation calculation depends on the bins’ usage pattern; that is, if some higher tones are in use then calculated attenuation will be ‘worse’ because those poor attenuation figures for those tone, because of their high frequency, will bring the total down. Is that correct?

If this is so, then attenuation is not really attenuation of the line, which may or may not be what we want, but attenuation of the signal. In any case asking for the “attenuation of the line” is meaningless anyway as you have to say “at what frequency?”. Over the years, using various modems and improved settings with lower downstream SNRM I have noticed that reported attenuation figures for downstream have crept up with every speed improvement. Twelve years ago d/s attn was reported as 60.5 dB and now albeit with a different modem it’s 64.5 dB and I attribute this to the usage of additional higher tones. My changing to G.992.3 (ADSL2) rather than G.992.1 (original ‘ADSL1’ spec) is one factor, because higher tones are now in use since ADSL2 supports 1-bit tones and old ADSL1 doesn’t iirc, thus putting additional weakest tones into service.

I don’t know enough about differences between models. If you are testing by switching between models then you are bound to get different downstream sync speeds unpredictably because of DLM and because of changes in line conditions as well as differences in the capabilities of the modems. If the sync speed is different that could mean that the bit-loading spectrum has changed. In that is the case then the basis for the attenuation calculation may have changed too if additional tones have come into use, or the reverse. So as always switching between models has to be done with care because of the ‘noise’ that the very act of switching produces in the results.

Is it the case that the details of the attenuation calculation are in the standards specs somewhere?
« Last Edit: November 13, 2020, 09:08:05 PM by Weaver »
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burakkucat

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Re: Downstream line attenuation difference on modem routers
« Reply #17 on: November 13, 2020, 10:23:27 PM »

Is it the case that the details of the attenuation calculation are in the standards specs somewhere?

If it is, then I'm sure one of us (where "us" is defined as the Kitz community) would have found it and publicised the relevant URL . . .
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adslmax

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Re: Downstream line attenuation difference on modem routers
« Reply #18 on: November 14, 2020, 10:29:29 PM »

I have tested two modem & router now as it seem TP Link are much better with higher SNR and higher data rate with 0.50m dsl cable as the Openreach Modem has the lower data rate

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adslmax

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Re: Downstream line attenuation difference on modem routers
« Reply #19 on: November 14, 2020, 10:37:00 PM »

Three telephone sockets (bedroom unknown tel number, living room unknown tel number and hallway current on FTTC)

The photo at the top seem better cable from the telephone exchange rather than hallway thinner cable from the telephone exchange (this is master socket current on FTTC bottom photo)
« Last Edit: November 14, 2020, 10:42:56 PM by adslmax »
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adslmax

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Re: Downstream line attenuation difference on modem routers
« Reply #20 on: November 14, 2020, 10:48:27 PM »

The bin cupboard BT junction box showing no cable for the bedroom socket? The thick best cable but I can't find where it come from outside cable?
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Alex Atkin UK

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Re: Downstream line attenuation difference on modem routers
« Reply #21 on: November 15, 2020, 03:05:11 AM »

I would expect them all to be extensions of the same line.

Also looks to me like aluminium coming into that BT junction box, possibly why the line speeds have been rated down?
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adslmax

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Re: Downstream line attenuation difference on modem routers
« Reply #22 on: November 15, 2020, 03:37:34 AM »

Also looks to me like aluminium coming into that BT junction box, possibly why the line speeds have been rated down?

Maybe I ask PN to sent out Openreach engineer to see if the aluminum cable can be replaced a new one! I don't mind a one off charge £130
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re0

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Re: Downstream line attenuation difference on modem routers
« Reply #23 on: November 15, 2020, 04:46:45 AM »

Maybe I ask PN to sent out Openreach engineer to see if the aluminum cable can be replaced a new one! I don't mind a one off charge £130
For what purpose, may I ask? So your attainable rates can be higher? So that your G.fast estimated speeds can be higher even though you'll never order it? I don't know, but I doubt they would raise it to OR since there is no fault. Sure, you could say there is a fault and accept the one-off charge, but I think we both know they aren't going to replace your drop - and if they did, what difference is 10-15m going to make? And they're definitely not going to lay a new cable from the cabinet.

Try to stop thinking about it. Do you have anything else you can do at the moment to take your mind off this? It's not worth the time or money, and it's definitely not worth worrying about.
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tubaman

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Re: Downstream line attenuation difference on modem routers
« Reply #24 on: November 15, 2020, 09:18:10 AM »

Maybe I ask PN to sent out Openreach engineer to see if the aluminum cable can be replaced a new one! I don't mind a one off charge £130

Don't waste your time doing this as it's very unlikely to happen. Unless there is a definite fault they won't change the cable and you'll be throwing away £130.
 :)
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BT FTTC 80/20 Huawei Cab - Zyxel VMG8924-B10A
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