Noise Margin Changes

I have been messing around with a problem prone connection. Basically,
the house it about 500M away from the exchange, the speeds were under
2mbps at the start. After some calls, sky sent out their second
Netgear router. This increased the speed to 4-5mbps, but the Netgear
v1 would now connect at 3mbps but no 4mbps.

The only difference would be the V2 router would stuggle to get an IP.
Anyway after a bit of reflashing I changed the SNR margin to rock
bottom. The actually SNR value was at 1%. This brought up the Sync
rate.

Here is the issue, the router did a sync at 4.5mbps, with a noise
margin of 1.5db. As soon as the sync is done, 1 sec later the Noise
margin jumps to 8db, but the router has not resync'ed or nothing. Do a
manual re-sync does not increase the speed but the same thing just
happens again and again. As soon as the sync is completed and waiting
for the IP, the noise margin increase. Its the same at the test
socket.

What exactly I am supposed to report here, to have it fixed.

Another note is that it seem that there is high noise, using DMT it is
clear that every tone up to 1Mhz is coming through onto the line but
the attenuation is still 55db.

The physical line is a little old in terms of installation. The Drop
wire is black, but it feeds into a Junction box of some type which
then another cable to a NTE5 . The junction box is outside of the
property on the Soffit's. There is no noise/crackling on the line, so
can rule out moisture surely. No Idea on the materials in the junction
box, its a little hard to reach.

Just to add, it wa the V1 Router that was re-flashed and the speed
increased from 3mbps to 4.5mbps

On 4 Aug, 17:12, ato_...@hotmail.com wrote:
> > Another note is that it seem that there is high noise, using DMT it is
> > clear that every tone up to 1Mhz is coming through onto the line but
> > the attenuation is still 55db.
>
> Thee 55db attenuation when you are 500M from the exchange
> might account for your speed problem.
>
> > Here is the issue, the router did a sync at 4.5mbps, with a noise
> > margin of 1.5db. As soon as the sync is done, 1 sec later the Noise
> > margin jumps to 8db,
>
> You are trying to force the line to run at 1.5db and it can't, so
> it immediately jumps to 8db, and a slower speed.

False, in theory it should do that, but it does not. That is what is
baffling me. It connects at 1.5db, then it maintains the speed of
4.5mbps, but the noise margin has changed to 8db at the same speed,
with no re-sync, and then it gets the IP.

> At 1.5db the error rate is probably high and why there is
> a delay getting an IP address until the SNR goes to 8db.

Thats what I thought, though it only happens on the V2 router, the V1
gets the IP immediately, possibly just because of the difference in
hardware.

> I'd suspect that if in fact your cable run is as you quote
> 500M, there is a cable problem, possibly waterlogged
> cable, or a dry joint, but the latter usually shows up
> as a voice problem as well.

Solution? There are no problems at all with phone line, totally
silent.


> You need a decent ISP who can get it investigated,
> Sky are not noted for this.
> There are hand held test sets like-------
> Ideal for ADSL2+ link installation and maintenance, the
> EXD-350 Advanced ADSL2+ Tester allows technicians
> to test copper loop quality, verify ADSL2+ performance
> and validate Internet connectivity.
> They also cover plain ADSL.
> Openreach should have similar equipment.
> Keep leaning on Sky to fix it or migrate with your
> wallet.

On Mon, 4 Aug 2008 08:21:03 -0700 (PDT), naza wrote:
> I have been messing around with a problem prone connection. Basically,
> the house it about 500M away from the exchange, the speeds were under
> 2mbps at the start. After some calls, sky sent out their second
> Netgear router. This increased the speed to 4-5mbps, but the Netgear
> v1 would now connect at 3mbps but no 4mbps.
>
> The only difference would be the V2 router would stuggle to get an IP.
> Anyway after a bit of reflashing I changed the SNR margin to rock
> bottom. The actually SNR value was at 1%. This brought up the Sync
> rate.
>
> Here is the issue, the router did a sync at 4.5mbps, with a noise
> margin of 1.5db. As soon as the sync is done, 1 sec later the Noise
> margin jumps to 8db, but the router has not resync'ed or nothing. Do a
> manual re-sync does not increase the speed but the same thing just
> happens again and again. As soon as the sync is completed and waiting
> for the IP, the noise margin increase. Its the same at the test
> socket.
>
> What exactly I am supposed to report here, to have it fixed.
>
When you do find a fault report that actually gets Sky to do something
useful/relevant/effective could you let me know as well, please?
Ever since my line was DLM'd the speed and noise margins have been
all over the place. I started monitoring it and have come to the
conclusion that the DG834GT starts off with a high ADSL speed (~14MBit/s)
until the connection gets used. As soon as there's any significant traffic
the noise margin drops by about 6dB and the modem re-trains down to 3MBit/s.
(Yes, I know a 6dB drop should only halve the line speed).

After that it may, or may not re-train back up to 14Mbit/s with a restored
SNR. Each time it decides to change it's speed, I lose ADSL for a couple
of minutes.
In the past week my "Max" connection has spent about 1/3rd of it's time
at 3-4MBit/s and I'm seeing a total uptime of about 99%.
The only response I got from Sky when I emailed in a fault report was
an automated survey asking me about which lights were flashing on the modem.
I sent it back with a 10,000 line log of the past week's activity - so far
they've had it for over a week with no reply.
Bah!


--
.. Pete Lynch I have learned from my mistakes and
.. Marlow ... I am sure I can repeat them exactly
.. www.pete-lynch.com --- Peter Cooke.

On Mon, 4 Aug 2008 19:27:53 GMT, (E-Mail Removed) wrote:
>
>> The only response I got from Sky when I emailed in a fault report was
>> an automated survey asking me about which lights were flashing on the
>> modem.
>
> Next comes reformat your drive and reinstall your OS.

Followed no doubt by a fault closure notice. Obviously since I
responded to their automated email my ADSL must be working.
Therefore the incident can now be closed - chalk up another
satisfied customer.

--
.. Pete Lynch I have learned from my mistakes and
.. Marlow ... I am sure I can repeat them exactly
.. www.pete-lynch.com --- Peter Cooke.