Noise and attenuation

My connection shows
local line attenuation 63 dB
remote line attenuation 31.5dB
Local SNR Margin 7.5dB
Remote SNR 17dB

I live a long way from the exchange and BT only recently agreed to connect
me despite the long wire length to the exchange.
My question is that sometimes whewn I connect I get Local SNR Margin of 2
or 3 dB and sometimes 7 or 8.
How does this happen? Is it unusual to connect with 3dB and still get
braodband running. It works OK at the lower levels but drops out
occasionally.
Geoff

Geoff Venn wrote:
> My connection shows
> local line attenuation 63 dB
> remote line attenuation 31.5dB
> Local SNR Margin 7.5dB
> Remote SNR 17dB
>
> I live a long way from the exchange and BT only recently agreed to
> connect me despite the long wire length to the exchange.
> My question is that sometimes whewn I connect I get Local SNR
> Margin of 2 or 3 dB and sometimes 7 or 8.
> How does this happen? Is it unusual to connect with 3dB and still
> get braodband running. It works OK at the lower levels but drops
> out occasionally.
> Geoff

Anything below a SNR of 6db can cause you all sorts of problems, slow
speends, drop outs etc....

Have you tried disconnecting all extension wiring & pluging into the master
to see what your results are? If it does make an improvement there are a
few things you could try. Now if you're using the only telephone socket on
the line it becomes more problematic...

On Fri, 24 Sep 2004 20:11:14 +0100, Kráftéé wrote:

> Geoff Venn wrote:
>> My connection shows
Whats odd is that I can reboot the router, without touching anything in
the house, and get a "clean line" at 7 or 8dB. Is there an external
influence at work here?
Geoff

>> local line attenuation 63 dB
>> remote line attenuation 31.5dB
>> Local SNR Margin 7.5dB
>> Remote SNR 17dB
>>

>
> Anything below a SNR of 6db can cause you all sorts of problems, slow
> speends, drop outs etc....
>
> Have you tried disconnecting all extension wiring & pluging into the master
> to see what your results are? If it does make an improvement there are a
> few things you could try. Now if you're using the only telephone socket on
> the line it becomes more problematic...

On Fri, 24 Sep 2004 20:17:40 +0100, in article
<(E-Mail Removed)> Geoff Venn
<(E-Mail Removed)> wrote:

> Whats odd is that I can reboot the router, without touching anything in
> the house, and get a "clean line" at 7 or 8dB. Is there an external
> influence at work here?

The router trains the modem at the point where it starts the connection
process and once it has trained the allocation of the various 4kHz signal
'bins' is fixed until the modem is reset or the connection drops and it
has to restart itself.

What you're seeing is that the retraining deals with the noise that is
appearing by adjusting the frequency bin usage to minimise the effect of
that noise spectrum at that point in time. If the noise subsequently
changes its spectral characteristics, then the modem will see the SNR
decline and the error rate will increase. At some point this process leads
to a line drop and another retraining cycle.

--

Brian Morrison

please observe reply-to address

Geoff Venn wrote:

> My connection shows
> local line attenuation 63 dB
> remote line attenuation 31.5dB
> Local SNR Margin 7.5dB
> Remote SNR 17dB
>


Sorry to side track this, but could someone explain the relevance of
these figures please.

--
Regards


David G
(remove r u n)

On Sat, 25 Sep 2004 14:20:12 +0100, Brian Morrison wrote:

> On Fri, 24 Sep 2004 20:17:40 +0100, in article
> <(E-Mail Removed)> Geoff Venn
> <(E-Mail Removed)> wrote:
>
Thanks Brian, that explains it. I've noticed that using the phone can
cause changes in the SNR that can persist and which change if I reboot.
Geoff>
>
> What you're seeing is that the retraining deals with the noise that is
> appearing by adjusting the frequency bin usage to minimise the effect of
> that noise spectrum at that point in time. If the noise subsequently
> changes its spectral characteristics, then the modem will see the SNR
> decline and the error rate will increase. At some point this process
> leads to a line drop and another retraining cycle.

On Sat, 25 Sep 2004 17:02:12 +0100, David G <notreallyhere@sure>
wrote:

>Geoff Venn wrote:
>
>> My connection shows
>> local line attenuation 63 dB
>> remote line attenuation 31.5dB
>> Local SNR Margin 7.5dB
>> Remote SNR 17dB
>>
>
>
>Sorry to side track this, but could someone explain the relevance of
>these figures please.

Local means downstream (i.e. the figures relevant to data coming from
the internet to your PC), while remote means upstream (i.e. relevant
to data going from your PC to the internet).

Attenuation is the loss of signal, expressed in Decibels (dB). Until
the 6th, you generally could not get 512K ADSL if the downstream
attenuation was more than 60dB. The lower the figure, the stronger the
signal you are getting.

SNR is Signal-to-Noise Ratio, again expressed in dB. With this one,
the higher the value the better. I've seen suggestions that anything
under 10 is likely to cause problems, and anything under about 5 is
likely to be unworkable.

"David G" <notreallyhere@sure> wrote in message
news:(E-Mail Removed)...
> Geoff Venn wrote:
>
>> My connection shows local line attenuation 63 dB
>> remote line attenuation 31.5dB
>> Local SNR Margin 7.5dB
>> Remote SNR 17dB
>>
>
>
> Sorry to side track this, but could someone explain the relevance of these
> figures please.
>
> --
> Regards
>
>
> David G
> (remove r u n)

I would like to ask where you can obtain these readings my modem/router
(Netgear DG814) does appear to show them anywhere

Regards

Roy

Alex Heney wrote:
>
> Local means downstream (i.e. the figures relevant to data coming from
> the internet to your PC), while remote means upstream (i.e. relevant
> to data going from your PC to the internet).
>
> Attenuation is the loss of signal, expressed in Decibels (dB). Until
> the 6th, you generally could not get 512K ADSL if the downstream
> attenuation was more than 60dB. The lower the figure, the stronger the
> signal you are getting.
>
> SNR is Signal-to-Noise Ratio, again expressed in dB. With this one,
> the higher the value the better. I've seen suggestions that anything
> under 10 is likely to cause problems, and anything under about 5 is
> likely to be unworkable.

Thanks

--
Regards


David G
(remove r u n)

In message <cj4mgr$o5$(E-Mail Removed)>, RChick
<(E-Mail Removed)> writes
>I would like to ask where you can obtain these readings my modem/router
>(Netgear DG814) does appear to show them anywhere

Some ADSL equipment, including your DG814, doesn't give such
information.



David
--
David Wood
(E-Mail Removed)