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Author Topic: Variable Downstream Attenuation  (Read 2357 times)

mywifeshusband

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Variable Downstream Attenuation
« on: September 28, 2007, 05:21:05 PM »

Hello Folks Me again. Just a diffeent forum!
Still the same problem with BT and I need to be quite sure of my facts.  I belive from what I have read that, given the same router and the same conection configuration that the day to day & hour to hour Downstream attenuation should not change. At least if there is no fault, or shall we say 'anomoly' on the line: both of which are clearly BT's responsibility to sort out and fix.

If this is the case then I must have proved the impossible:-

Please See here:-
 27/9/2007 @ 07:50 also at 15:15 the same afternoon.

Local Tx. Power(dB)  : 11.95               Remote Tx.Power(dB)   : 15.13
Local Line Atten(dB) : 48.5  :)               Remote Line Atten(dB) : 31.5
Local SNR Margin(dB) : 7.0                 Remote SNR Margin(dB) : 24.0
Up SValue            : 1                   Down SValue           : 1
Up DValue            : 1                   Down DValue           : 1

           UpIntrlvd UpFast DownIntrlvd DownFast
AS0(kbps): -         -      0           1152
AS1(kbps): -         -      0           0
LS0(kbps): 0         288  ::)   -           -
LS1(kbps): 0         0      -           -
RValue   : 0         0      0           0

and here;
6/8/07 @ 15:35


Local Tx. Power(dB)  : 11.95               Remote Tx.Power(dB)   : 15.30
Local Line Atten(dB) : 60.5   >:(              Remote Line Atten(dB) : 31.5
Local SNR Margin(dB) : 9.5                 Remote SNR Margin(dB) : 18.0
Up SValue            : 1                   Down SValue           : 1
Up DValue            : 1                   Down DValue           : 1

           UpIntrlvd UpFast DownIntrlvd DownFast
AS0(kbps): -         -      0           1280
AS1(kbps): -         -      0           0
LS0(kbps): 0         448   ???  -           -
LS1(kbps): 0         0      -           -
RValue   : 0         0      0           0

Sorry about the length of this post but I'm now putting my case to Othelo having given up any hope of getting anywhere with BT off shore, BT UK, and BT High level Helpdesks. I've been promised a solution, and a wireless hub router that works, so many times, neither of which have  happened, since being Maxed on 1/6/07. In fact I think I have now been de maxed if such a process is possible. See 'attenuated' upline Attenuation rates!
My downline Attenuation is different every time I check the parameters: somewhere between 48.5dB to 60.5 dB using the most reliable router I have, (my pre max) Voyager 205 on a 20 ft extension cable. BT Wireless routers vary between 60 & 63dB on my line even when plugged into the main socket. 
I think I'm right in saying that given my 3.05 Km crow flies distance from the Exchange BT should be able to give me something closer to the faster service of up to 2Mbps they said, (pre max,) was available for my phone number.
My contention is that if my Downstream Attenuation was steady at around 50dB rather than wandering about all over the place as it does, then we would not have a problem.
Please tell me I'm not barking up the wrong tree.
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roseway

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Re: Variable Downstream Attenuation
« Reply #1 on: September 28, 2007, 07:00:07 PM »

You're right to say that attenuation shouldn't change significantly. There will be small changes resulting from changes in the frequency spectrum of the connection, and different routers can report slightly different figures, but a 12 dB variation is way out of normal. If you're still seeing that much variation, then you must have a line fault (probably a high resistance fault) and BT have to fix it. The easiest option for you would be if there is audible crackling or hiss on the line. If there is then you can report it as a voice fault (dial 150) and they will pay attention quickly.

Your present figures certainly imply that you're on a fixed 1 Mbps connection and not ADSL Max. The previous figures were appropriate for Max on a high attenuation (60 dB) line. I suggest that you get the line fault fixed first, then push BT to re-max your connection.
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  Eric

mywifeshusband

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Re: Variable Downstream Attenuation
« Reply #2 on: October 01, 2007, 07:51:51 AM »

Thanks Roseway. Just as I  thought! As no one else has posted a reply and my posting has been up for a few days now, and presumably has been seen by BT too, I think I can take it that the concensus of telecoms technical expert opinion is of the same mind.

I have done a 17070 quiet line test and can hear nothing, but at my age, aural acuity of higher frequency sounds is probably not as good as once it was. :cry2: Do BT really think that this is an adequate test for line noise?
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roseway

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Re: Variable Downstream Attenuation
« Reply #3 on: October 01, 2007, 08:08:02 AM »

I'm not sure that you can assume that anyone from BT has seen your posting, but I don't think there's much doubt about the diagnosis. But the problem appears to be intermittent, and faults of this nature are commonly affected by the weather, so your line might crackle at some times and not at others. I think you're going to have to give this some time; monitor the router stats periodically and see if the high attenuation situation recurs, then try the quiet line test.

By the way, BT do have their own more sensitive equipment for measuring noise, but the quiet line test is just a quick and easy test which can be carried out at any time with no equipment being needed.
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  Eric

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Re: Variable Downstream Attenuation
« Reply #4 on: October 15, 2007, 05:37:07 PM »

Quote
You're right to say that attenuation shouldn't change significantly.

On 8Mbps ADSL I'd agree. On ADSL2+ then it varies significantly depending on where your ISP measures it. Remember that ADSL2+ uses frequencies above 2MHz so the attenuation figure (BT measure/measured at 300kHz but Be have test signals way above that which seem to be set according to the region you live in) is pretty much meaningless.

Its a guide sure but its a pretty poor guide. Line capacitance and local electrical noise rule all. Local noise is the killer if you have decent wiring and I can personally assure you that a 5 metre "Argos-type" telephone extension is quite capable of knocking 5Mbps off an ADSL2+ connection.

My connection stats for your perusal (I need stability above all else, hence me increasing the SNR) :

Link Information
         
Uptime:   14 days, 18:20:23
Modulation:   G.992.5 Annex A
Bandwidth (Up/Down) [kbps/kbps]:   1,351 / 18,857
Data Transferred (Sent/Received) [MB/GB]:   382.09 / 4.37
Output Power (Up/Down) [dBm]:   12.0 / 17.5
Line Attenuation (Up/Down) [dB]:   10.5 / 23.5
SN Margin (Up/Down) [dB]:   7.5 / 8.0
Vendor ID (Local/Remote):   TMMB / µ
Loss of Framing (Local/Remote):   0 / 0
Loss of Signal (Local/Remote):   0 / 0
Loss of Power (Local/Remote):   0 / 0
Loss of Link (Remote):   0
Error Seconds (Local/Remote):   2,244 / 0
FEC Errors (Up/Down):   0 / 0
CRC Errors (Up/Down):   9,717 / 3,501
HEC Errors (Up/Down):   11,480 / 1,865

I have a "gap" at about 2.1MHz due to interference from a defence contractors site, but the line is capable of running at 24Mbps with a 1.5dB margin for 22 hours/day (there will be two disconnections in the other two hours). ADSL2+ is a lot of fun if you know how to use the DMT Tool sensibly but I can see crosstalk and impulse noise becoming support nightmares as BT roll out 21CN.

Error seconds are directly related to CRC Errors (Down) as the line has Be's "fastpath" set (it is still interleaved (4)).
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