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Standard User WilliamGrimsley
(committed) Fri 10-Mar-17 15:19:10
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Line Attenuation Changing


[link to this post]
 
Hi guys,

Any ideas what could be going on here? My line attenuation figure keeps moving around, recently it was 26.3 but after restarting my router it's now 23.8 dB (I did this to remove the downstream CRC's, ES' and SES' after a DLM resync which changed my downstream SNR margin from 4 to 5 dB). Surely that means my line is now significantly shorter? FEC's seem to be increasing but not CRC's, quiet line test seems to be ok (slight continuous noise).

Thanks for your help.

William

Edited by WilliamGrimsley (Fri 10-Mar-17 15:25:43)

Standard User WelshWArrior
(fountain of knowledge) Fri 10-Mar-17 15:24:15
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Re: Line Attenuation Changing


[re: WilliamGrimsley] [link to this post]
 
My line is usually around 18.5 but often jumps up to 28+ - I've never gotten to the bottom of it . Be interesting if you find a cause.

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Standard User WilliamGrimsley
(committed) Fri 10-Mar-17 15:26:26
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Re: Line Attenuation Changing


[re: WelshWArrior] [link to this post]
 
Yeah, no idea. Can only think it's a line issue...


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Standard User RobertoS
(elder) Fri 10-Mar-17 15:44:21
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Re: Line Attenuation Changing


[re: WilliamGrimsley] [link to this post]
 
Dunno, but the fact, (assuming both the SNRM figures you give at immediately post-sync as no other comparison is valid), that DLM will only have increased the margin because it feels the line is unstable, is your own restarting of the router could easily have started it considering if it needs to go back up to 6dB.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
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Standard User WilliamGrimsley
(committed) Fri 10-Mar-17 15:50:24
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Re: Line Attenuation Changing


[re: RobertoS] [link to this post]
 
No, the restarting of the router wouldn't have made any change, I simply do that to get a fresh connection after resync. No idea why it did do that as there were no errors... Must've been the 26000000 FEC's in nearly 2 days that did it. Yes, 26 million!

Edited by WilliamGrimsley (Fri 10-Mar-17 15:53:11)

Standard User WilliamGrimsley
(committed) Fri 10-Mar-17 15:58:42
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Re: Line Attenuation Changing


[re: WilliamGrimsley] [link to this post]
 
Is this of any help?

> adsl info --pbParams
adsl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 8497 Kbps, Downstream rate = 43376 Kbps
Bearer: 0, Upstream rate = 8497 Kbps, Downstream rate = 42767 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Discovery Phase (Initial) Band Plan
US: (7,32) (871,1205) (1972,2782)
DS: (33,859) (1216,1961) (2793,3959)
Medley Phase (Final) Band Plan
US: (7,32) (871,1205)
DS: (33,859) (1216,1961)
VDSL Port Details Upstream Downstream
Attainable Net Data Rate: 8497 kbps 43376 kbps
Actual Aggregate Tx Power: 5.5 dBm 12.1 dBm
====================================================================================
VDSL Band Status U0 U1 U2 U3 U4
D1 D2 D3
Line Attenuation(dB): 10.7 48.7 N/A N/A N/A 21.0 58.5 N/A
Signal Attenuation(dB): 10.7 48.2 N/A N/A N/A 32.4 58.1 N/A
SNR Margin(dB): 6.4 6.4 N/A N/A N/A 5.2 5.2 N/A
TX Power(dBm): -5.8 5.2 N/A N/A N/A 10.1 7.8 N/A
Administrator MrSaffron
(staff) Fri 10-Mar-17 16:02:00
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Re: Line Attenuation Changing


[re: WilliamGrimsley] [link to this post]
 
Maybe a band was used for a while and dropped again, thus affecting the aggregate attenuation

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User WilliamGrimsley
(committed) Fri 10-Mar-17 16:06:50
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Re: Line Attenuation Changing


[re: MrSaffron] [link to this post]
 
Yes, I thought it may be to do with that. The difference between D1 and D2 seems quite large though.
Administrator MrSaffron
(staff) Fri 10-Mar-17 19:00:11
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Re: Line Attenuation Changing


[re: WilliamGrimsley] [link to this post]
 
Have not looked up, but you might want to look at the frequencies each band occupies as this influences the attenuation, i.e. higher frequency gives higher attenuation

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User WWWombat
(knowledge is power) Sat 11-Mar-17 13:02:09
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Re: Line Attenuation Changing


[re: MrSaffron] [link to this post]
 
I've seen the aggregate power change when extra bands get added or removed, but not the attenuation value. In general, the attenuation shouldn't change - if it does, then my experience is the line is faulty, and it will play havoc with DSL.

However, when something goes wrong with the attenuation, the value tends to increase, not decrease. So I remain open to believing this is a problem with internal modem calculations rather than the line itself, as much as it being vice-versa.

On MDWS, it is obvious that the recent batch of results have lost D2 from the downstream "line attenuation" figures. It was always missing from the downstream "signal attenuation" figures, and a look at the historic "bits/tone" graphs confirms that D2 was never used.

The attenuation value ought to be connected to the results seen in the HLog graph, so it is worth looking there too.

On MDWS, the basic shape of Hlog, up to tone 1960, seems to be unchanged. The only real difference is that older graphs show a smattering of results up around tones 2800-3000. There are still a few reading up there, but considerably fewer.

Because the main, usable, part of Hlog (up to tone 1960) is unchanged, I'd say that there hasn't been a change to the line in a way that affects service. It might just be a pointer to watch out for the future, though.

As confirmation, the main SNR/tone graph doesn't seem to have changed much either. No change to service.
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