Noise margin deteriorates over time

Hi guys,

Wondered if you have any thoughts on a little problem I'm having with my
downstream ADSL noise margins.

This is how things stand at the moment:
ADSL Link Downstream Upstream
Connection Speed 2272 kbps 288 kbps
Line Attenuation 44 db 23 db
Noise Margin 26 db 31 db

However, that is after I removed the phone connection from my phone socket
and plugged it back in. Before that, my Downstream Noise Margin was a
pathetic 5db. Upstream stays pretty much constant as it is now.

My ISP is Force 9, my ADSL router is a Netgear DG834G (the 1st one) and
plugged into the only socket in the house I have the following: directly
into the socket is my ADSL filter. Plugged into that is my router and a
socket splitter to allow my Sky+ and cordless phones to be plugged in.

Any thoughts? I can't believe the downstream can fluctuate by as much as
20db or so (it's dropped by 5db while writing this email), when the upstream
stays rock solid as it is. I've yet to notice any degradation in speeds,
but it doesn't bode well for ever getting 4 or 8mbps in the future.

Cheers,
Stephen

"Stephen Webber" <(E-Mail Removed)> wrote in
message news:42924a76$0$579$(E-Mail Removed)...
> Hi guys,
>
> Wondered if you have any thoughts on a little problem I'm having with my
> downstream ADSL noise margins.
>
> This is how things stand at the moment:
> ADSL Link Downstream Upstream
> Connection Speed 2272 kbps 288 kbps
> Line Attenuation 44 db 23 db
> Noise Margin 26 db 31 db
>
> However, that is after I removed the phone connection from my phone socket
> and plugged it back in. Before that, my Downstream Noise Margin was a
> pathetic 5db. Upstream stays pretty much constant as it is now.
>
> My ISP is Force 9, my ADSL router is a Netgear DG834G (the 1st one) and
> plugged into the only socket in the house I have the following: directly
> into the socket is my ADSL filter. Plugged into that is my router and a
> socket splitter to allow my Sky+ and cordless phones to be plugged in.
>
> Any thoughts? I can't believe the downstream can fluctuate by as much as
> 20db or so (it's dropped by 5db while writing this email), when the
> upstream stays rock solid as it is. I've yet to notice any degradation in
> speeds, but it doesn't bode well for ever getting 4 or 8mbps in the
> future.

What symptoms do you get when the noise margin starts to decrease?

I live about 100 metres from my local exchange and I'd be surprised if the
length of the wires was more than about 200 metres. It's new copper,
installed in the last 5 years. And yet on a 2 Mbps line using a Netgear
DG834GT router, I consistently get

ADSL Link Downstream Upstream
Connection Speed 2272 kbps 288 kbps
Line Attenuation 30 db 29 db
Noise Margin 6 db 6 db

If people are getting 20-30dB, my noise margin is rather low. I've checked
the results with the router plugged into my master socket as opposed to my
BT-installed extension, and there's no difference. In parallel with the BT
extension there are also three sockets on wiring that was installed by the
builder and which I presume (because it's wired into the back of the master
socket) I'm not allowed to disconnect temporarily to see if it makes any
difference.

And yet I can get almost 2 Mbps at times: using Force 9's speed test just
now, I've got 1.8 and 1.9 Mbps on two consecutive runs. The speed does vary
from time to time (the worst I've had is 0.9 Mbps; typically it's 1.5-1.8)
but I imagine that this is due to varying amounts of contention.


What factors affect noise margin? As well as the condition of the line
between my house and the exchange, is it also affected by any wiring
connected to my master socket?

On Mon, 23 May 2005 22:26:20 +0100, "Stephen Webber"
<(E-Mail Removed)> wrote:

>Wondered if you have any thoughts on a little problem I'm having with my
>downstream ADSL noise margins.

the reported SNR of some Netgear kit appears to drift down with time,
according to user reports. One idea would be to flash it up to the
latest firmware

http://kbserver.netgear.com/products/DG834G.asp

If you do a disconnect/reconnect or a reboot from the web interface it
should go back to its original value if this hypothesis is correct.

If you're worried about the line quality borrow or Ebay a BT Voyager
105 USB modem as a piece of test kit.

Phil
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