Lies, damn lies and router noise margin statistics

[Didn't intend it to but this turned into a bit of an opus. So, summary:

Don't believe what your modem tells you. Two different makes can't even get
close to agreeing what the noise margin is for a given line]


For the last ten months I've been using a 3Com 3CRWE754G72-A ADSL modem
router. For an average of two hours a day, the noise margin drops low enough
that I'm disconnected - see www.mason.sh/3com.gif for a graph of the last
four months, sampled every ten minutes, showing the noise margin reported by
the 3Com.

The drop outs are almost exclusively between the hours of 10pm and 1am.

Given that I don't expect to get too far with Pipex or BT when I ask for
a engineer to visit at 10.30pm to check out a line that's 6.6km from the
exchange as the wire goes, in an area where the neighbours are being turned
down for ADSL left, right and centre and when the line was previously
delivered via TPON, I've been prepared to put up with it and revert to
dialup when needed.

However, reading recent posts on here about the ability of Vigor and Zyxel
kit to better handle poor line conditions, I thought I'd give them a try.

So with the help of ebay and for the grand sum of twelve quid delivered, I'm
now the proud owner of a Zyxel 645R ADSL router. Plug it in yesterday, get
it
all configured (telnet only, cool....) and bingo, I'm connected. Spend ten
minutes on Google trying to find out how to get some line stats out of it
and with the help of the Italian equivalent of utb, I find out 'wan adsl
line near' is the required syntax:

relative capacity occupation: 29%
noise margin downstream: 19.5 db
output power upstream: 12.0 dbm
attenuation downstream: 66.5 db

Hmmm. Two minutes ago when I disconnected the 3Com, it was claiming 13dB and
given I've *never* seen it higher than 15.5dB, where does 19.5dB come from?

Also points towards the 3Com not being able to handle integers higher than
63 for
attenuation - I'm so used to looking at "-63dB" it's interesting to see what
it really is.

Change back to the 3Com and it really does think that 13dB is what it's
hearing.

Skipping forward to 10.15pm last night and the line goes dead - 3Com reckons
4dB
is all I've got. Swap over to the Zyxel and.........

9dB and a working connection.

Zyxel keeps the line up for another 30 minutes before it reckoned the line
was below 6dB at which point it dropped the line too.

Now, just need to get hold of a Vigor for twelve quid as well :-)

On Monday, in article
<(E-Mail Removed)> (E-Mail Removed)
"Grant" wrote:

> [Didn't intend it to but this turned into a bit of an opus. So, summary:
>
> Don't believe what your modem tells you. Two different makes can't even get
> close to agreeing what the noise margin is for a given line]

[snippage]

> So with the help of ebay and for the grand sum of twelve quid delivered, I'm
> now the proud owner of a Zyxel 645R ADSL router. Plug it in yesterday, get
> it
> all configured (telnet only, cool....) and bingo, I'm connected. Spend ten
> minutes on Google trying to find out how to get some line stats out of it
> and with the help of the Italian equivalent of utb, I find out 'wan adsl
> line near' is the required syntax:
>
> relative capacity occupation: 29%
> noise margin downstream: 19.5 db
> output power upstream: 12.0 dbm
> attenuation downstream: 66.5 db
>
> Hmmm. Two minutes ago when I disconnected the 3Com, it was claiming 13dB and
> given I've *never* seen it higher than 15.5dB, where does 19.5dB come from?

The obvious question is whether you were using the same lead between
modem and wall-socket. And, even if you were, my own experience with
other stuff would have me wondering if there was something about the
physical connectors. (And the damaged lead I had recently didn't look
obviously damaged.)

Doesn't sound quite right for a long-term problem...

--
David G. Bell -- SF Fan, Filker, and Punslinger.

"I am Number Two," said Penfold. "You are Number Six."

On Mon, 4 Jul 2005 16:09:51 +0100, "Grant" <(E-Mail Removed)> wrote:

>Hmmm. Two minutes ago when I disconnected the 3Com, it was claiming 13dB and
>given I've *never* seen it higher than 15.5dB, where does 19.5dB come from?

there are 256 frequency bands in an ADSL connection. A modem with a
different connecting strategy might use more of them with less bits
carried on each, that would potentially give a higher margin.

3com kit has let people down before on dodgy lines eg guy with useless
connection on 3com buys Zoom X3 and achieves reliable connection.

http://www.yarwell.demon.co.uk/plot.html and
http://www.yarwell.demon.co.uk/ADSL%20Status.htm illustrate the point
about strategy. I don't even know if all kit reports the same thing -
is the margin an average, the worst value, at a particular frequency
or what ?

The hard bit is pinning down what is due to the line and what to the
kit !

Phil

On Mon, 4 Jul 2005 16:09:51 +0100, Grant wrote:

>see www.mason.sh/3com.gif for a graph

How did you do that?


--
Nigel M

"Nigel Molesworth" (E-Mail Removed) wrote in message
news:(E-Mail Removed)
> On Mon, 4 Jul 2005 16:09:51 +0100, Grant wrote:
>
>> see www.mason.sh/3com.gif for a graph
>
> How did you do that?

Scheduled Perl script that logs in to the router admin page, grabs the noise
margin figure and sticks it in a text file as well as HH:MM:YYYY:MMD.

Excel macro sucks text file in and voila.

""David G. Bell"" (E-Mail Removed) wrote in message
news:(E-Mail Removed)
>
> The obvious question is whether you were using the same lead between
> modem and wall-socket.

Yep. Unplugged from the 3Com, moved 1" up and plugged into the Zyxel.

> And, even if you were, my own experience with
> other stuff would have me wondering if there was something about the
> physical connectors.

BT digital face plate supplied and fitted by the engineer who replaced my HH
with BB. Standard 1m RJ11<>RJ11 lead goes into data socket, nothing at all
plugged into 'voice' socket - I use my other line for voice.

"Grant" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> [Didn't intend it to but this turned into a bit of an opus. So, summary:
>
> Don't believe what your modem tells you. Two different makes can't even
get
> close to agreeing what the noise margin is for a given line]
>
>
> For the last ten months I've been using a 3Com 3CRWE754G72-A ADSL modem
> router. For an average of two hours a day, the noise margin drops low
enough
> that I'm disconnected - see www.mason.sh/3com.gif for a graph of the last
> four months, sampled every ten minutes, showing the noise margin reported
by
> the 3Com.
>
> The drop outs are almost exclusively between the hours of 10pm and 1am.
>
> Given that I don't expect to get too far with Pipex or BT when I ask for
> a engineer to visit at 10.30pm to check out a line that's 6.6km from the
> exchange as the wire goes, in an area where the neighbours are being
turned
> down for ADSL left, right and centre and when the line was previously
> delivered via TPON, I've been prepared to put up with it and revert to
> dialup when needed.
>
> However, reading recent posts on here about the ability of Vigor and Zyxel
> kit to better handle poor line conditions, I thought I'd give them a try.
>
> So with the help of ebay and for the grand sum of twelve quid delivered,
I'm
> now the proud owner of a Zyxel 645R ADSL router. Plug it in yesterday, get
> it
> all configured (telnet only, cool....) and bingo, I'm connected. Spend ten
> minutes on Google trying to find out how to get some line stats out of it
> and with the help of the Italian equivalent of utb, I find out 'wan adsl
> line near' is the required syntax:
>
> relative capacity occupation: 29%
> noise margin downstream: 19.5 db
> output power upstream: 12.0 dbm
> attenuation downstream: 66.5 db
>
> Hmmm. Two minutes ago when I disconnected the 3Com, it was claiming 13dB
and
> given I've *never* seen it higher than 15.5dB, where does 19.5dB come
from?
>
> Also points towards the 3Com not being able to handle integers higher than
> 63 for
> attenuation - I'm so used to looking at "-63dB" it's interesting to see
what
> it really is.
>
> Change back to the 3Com and it really does think that 13dB is what it's
> hearing.
>
> Skipping forward to 10.15pm last night and the line goes dead - 3Com
reckons
> 4dB
> is all I've got. Swap over to the Zyxel and.........
>
> 9dB and a working connection.
>
> Zyxel keeps the line up for another 30 minutes before it reckoned the line
> was below 6dB at which point it dropped the line too.
>
> Now, just need to get hold of a Vigor for twelve quid as well :-)

I have just upgraded to different firmware version on my DSL-504 router and
get very different s/n ratio 12dB on one firmware and 25 dB on the other.
All same hardware just different firmware. Looking in the include files
which comprise the compiled firmware load, there are entries such as TX gain
RX gain and other settings. If the default gain settings are different
which they more than likely would be with different makes of router then you
will definitely get different s/n ration figures reported.

Grant wrote:
>
>
> relative capacity occupation: 29%
> noise margin downstream: 19.5 db
> output power upstream: 12.0 dbm
> attenuation downstream: 66.5 db
>
> Hmmm. Two minutes ago when I disconnected the 3Com, it was claiming 13dB and
> given I've *never* seen it higher than 15.5dB, where does 19.5dB come from?
>


The 3com has 4 times as much noise in its' front end ? Does not move to
cleaner bands in the same way ?

Bill

"Alt Beer" (E-Mail Removed) wrote in message
news:yXhye.15341$(E-Mail Removed)
>
> I have just upgraded to different firmware version on my DSL-504
> router and get very different s/n ratio 12dB on one firmware and 25
> dB on the other.

Was that the router that needed a firmware upgrade because they had the SNR
and attenuation figures reversed?

On Mon, 4 Jul 2005 23:01:26 +0100, "Grant" <(E-Mail Removed)> wrote:

>Was that the router that needed a firmware upgrade because they had the SNR
>and attenuation figures reversed?

Dlink, yes.

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.