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uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

Large variations in Noise Margin?



 
 
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  #1  
Old March 5th 05, 01:41 PM posted to uk.telecom.broadband
Gareth
external usenet poster
 
Posts: 75
Default Large variations in Noise Margin?

Does a fluctuating variation in downstream Noise Margin, over a period of a
few hours, from 26 db to 14 db suggest a line fault?

Gareth.


  #2  
Old March 5th 05, 05:11 PM posted to uk.telecom.broadband
John Steele
external usenet poster
 
Posts: 62
Default Large variations in Noise Margin?

I have been noticing for many months that my attenuation (not so much my
SNR) has been varying. As there is a possibility of a speed enhancement (I
am with Plusnet) in the near future I decided to write some code to monitor
the situation. I had been thinking about this for a long time.

My attenuation has been varying from 53 to 58 db which is uncomfortably
close to the old limit of 60 dB. the SNR however is quite good. When I
developed the code (more later) and have been monitoring the situation the
attenuation suddenly dropped to 52.5 and (apart from one sample) has stayed
there ever since! I have now been running the sampling program since 28
February. I did have some earlier results from a few days before that but I
have discarded them as the format was not quite the same.

My sampling program depends on a Freeware package called Teraterm and is
customised for my SAR110 router. It should be relatively easy to customise
for any other router with a telnet interface. The results are displayed in
Internet Explorer (sorry it does not work for Firefox at the moment). The
data can be generated in CVS and/or XML format by simple configuration. The
IE display uses XML data islands.

For those of you interested here are the results to date sampled two to
three times a day. http://www.soroban.co.uk/routerstats/statistics.htm

A page describing the macro code and how to configure it is
http://www.soroban.co.uk/routerstats. This contains download links for
Teraterm and for the macro code and necessary HTML pages to display the
data.
http://www.soroban.co.uk/routerstats

I had been (possibly still am) interested to see if I could find any
correlation between my varying attenuation and the weather or any other
external factors. I will have to wait until it changes again however to do
that - the jump to 55 db was around the time I needed to reboot my router.

John Steele
jcs AT soroban DOT co DOT uk

"Brian Morrison" wrote in message
news
Gareth wrote:
Does a fluctuating variation in downstream Noise Margin, over a period of
a few hours, from 26 db to 14 db suggest a line fault?


Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes it
dips somewhat, I've seen values between 7 and 24dB at various times. THe
modem doesn't lose sync, in fact if I didn't monitor the stats I'd
probably not know it happens.

The low SNR periods are quite short, the longest I've seen was somewhere
around 15dB for a few hours but not static during that time.

I think it is probably interference that gets into a phone line pair in
the same cable and is related to a faulty household item somewhere in the
two villages served by the exchange.

--

Brian Morrison

please observe reply-to address



  #3  
Old March 5th 05, 06:42 PM posted to uk.telecom.broadband
Tony
external usenet poster
 
Posts: 57
Default Large variations in Noise Margin?

Brian Morrison wrote on Sat, 5 Mar 2005 at
15:19:57:
Gareth wrote:
Does a fluctuating variation in downstream Noise Margin, over a
period of a few hours, from 26 db to 14 db suggest a line fault?


Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes it
dips somewhat, I've seen values between 7 and 24dB at various times.
THe modem doesn't lose sync, in fact if I didn't monitor the stats I'd
probably not know it happens.

The low SNR periods are quite short, the longest I've seen was
somewhere around 15dB for a few hours but not static during that time.

I think it is probably interference that gets into a phone line pair in
the same cable and is related to a faulty household item somewhere in
the two villages served by the exchange.


Just to add another example of interference, I have an agricultural
electric fence running nearby. When a poor joint causes it to spark for
a while, my ADSL SNR drops from its usual 35 dB to 15 or 20 dB. The
attenuation stays constant, as expected in that scenario, at 42 dB.

--
Tony
  #4  
Old March 6th 05, 07:20 PM posted to uk.telecom.broadband
Gareth
external usenet poster
 
Posts: 75
Default Large variations in Noise Margin?


"Brian Morrison" wrote in message
news
Gareth wrote:
Does a fluctuating variation in downstream Noise Margin, over a period of
a few hours, from 26 db to 14 db suggest a line fault?


Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes it
dips somewhat, I've seen values between 7 and 24dB at various times. THe
modem doesn't lose sync, in fact if I didn't monitor the stats I'd
probably not know it happens.


Well, mine is fluctuating wildly (from anywhere between 12 to 26) polled
every 5 seconds.

I've also been having problems with voice calls as well as ADSL loss of
synch. 3 BT engineers in a few days have given their opinions. The first 2
explained that new cable would have to be laid (because of low insulation on
the existing cable) but as this would be an expensive job another engineer
may be asked to give an opinion. Sure enough he did and found another pair
of copper wires coming in to the house which he duly connected. This seems
to have solved the voice call problem but not the ADSL problem and the line
noise is now fluctuating wildly.

I've been having problems since November and, not seeing a solution, I'm on
the verge of writing ADSL off as a lost cause and moving to NTL instead.

Gareth.


  #5  
Old March 6th 05, 08:36 PM posted to uk.telecom.broadband
kraftee
external usenet poster
 
Posts: 1,069
Default Large variations in Noise Margin?

Brian Morrison wrote:
Gareth wrote:
"Brian Morrison" wrote in message
news
Gareth wrote:

Does a fluctuating variation in downstream Noise Margin, over a
period of a few hours, from 26 db to 14 db suggest a line fault?

Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes
it dips somewhat, I've seen values between 7 and 24dB at various
times. THe modem doesn't lose sync, in fact if I didn't monitor the
stats I'd probably not know it happens.



Well, mine is fluctuating wildly (from anywhere between 12 to 26)
polled every 5 seconds.


OK, that is a significant difference from what you posted previously,
it sounds like there is either a line fault or a continuous source of
impulsive noise.


I've also been having problems with voice calls as well as ADSL loss
of synch. 3 BT engineers in a few days have given their opinions.
The first 2 explained that new cable would have to be laid (because
of low insulation on the existing cable) but as this would be an
expensive job another engineer may be asked to give an opinion. Sure
enough he did and found another pair of copper wires coming in to
the house which he duly connected. This seems to have solved the
voice call problem but not the ADSL problem and the line noise is
now fluctuating wildly.


Right, so has the 3rd engineer simply changed the local drop cable
over? If so then the connection to the exchange from the nearest
junction cabinet may be the problem, hence the comments of the first
two engineers.


Which is completely the wrong practice as if the cable is going faulty it
_WILL_ affect all pairs, which (if I'm reading between the lines correctly)
is UG anyway (hence the costs in getting it changed).

Keep reporting the fault, it sounds like you've had 2 honest engineers & 1
FRS points chaser, can't help but wonder what the first 2 did about the
problem though...


  #6  
Old March 7th 05, 08:05 PM posted to uk.telecom.broadband
Gareth
external usenet poster
 
Posts: 75
Default Large variations in Noise Margin?


"kraftee" [email protected]& die.com wrote in message
...
Brian Morrison wrote:
Gareth wrote:
"Brian Morrison" wrote in message
news
Gareth wrote:

Does a fluctuating variation in downstream Noise Margin, over a
period of a few hours, from 26 db to 14 db suggest a line fault?

Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes
it dips somewhat, I've seen values between 7 and 24dB at various
times. THe modem doesn't lose sync, in fact if I didn't monitor the
stats I'd probably not know it happens.


Well, mine is fluctuating wildly (from anywhere between 12 to 26)
polled every 5 seconds.


OK, that is a significant difference from what you posted previously,
it sounds like there is either a line fault or a continuous source of
impulsive noise.


I've also been having problems with voice calls as well as ADSL loss
of synch. 3 BT engineers in a few days have given their opinions.
The first 2 explained that new cable would have to be laid (because
of low insulation on the existing cable) but as this would be an
expensive job another engineer may be asked to give an opinion. Sure
enough he did and found another pair of copper wires coming in to
the house which he duly connected. This seems to have solved the
voice call problem but not the ADSL problem and the line noise is
now fluctuating wildly.


Right, so has the 3rd engineer simply changed the local drop cable
over? If so then the connection to the exchange from the nearest
junction cabinet may be the problem, hence the comments of the first
two engineers.


Which is completely the wrong practice as if the cable is going faulty it
_WILL_ affect all pairs, which (if I'm reading between the lines
correctly) is UG anyway (hence the costs in getting it changed).

Keep reporting the fault, it sounds like you've had 2 honest engineers & 1
FRS points chaser, can't help but wonder what the first 2 did about the
problem though...


Thanks Brian and Kraftee.

Kraftee, you are spot on. Yes the cable is underground and all engineers
explained that the cost of having it replaced (including digging) would lead
to *all* other options being exhausted. The option that was chosen was to
use a spare pair coming in to the home from a box about 40 metres away (and
one that was presumably provided so that an extra line could be provided if
needed)

The second engineer even asked me to sign a form giving permission for
digging on a small area of grass outside the home so that the underground
cable could be replaced. The first engineer explained that there wasn't much
point swapping pairs because the cable itself was faulty. Because it was an
intermittent fault however even the first faulty tested pair wasn't always
showing a fault.

Now I'm buggered though: whilst the downstream attenuation has dropped by
2db the chaotic line noise margin is such that a 2Mbps service will be out
of the question (but it does seem to be supporting a 1Mbps service). Can't
complain too much I suppose.

Gareth.


  #7  
Old March 7th 05, 10:58 PM posted to uk.telecom.broadband
kraftee
external usenet poster
 
Posts: 1,069
Default Large variations in Noise Margin?

Gareth wrote:
"kraftee" [email protected]& die.com wrote in message
...
Brian Morrison wrote:
Gareth wrote:
"Brian Morrison" wrote in message
news
Gareth wrote:

Does a fluctuating variation in downstream Noise Margin, over a
period of a few hours, from 26 db to 14 db suggest a line fault?

Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However,
sometimes it dips somewhat, I've seen values between 7 and 24dB
at various times. THe modem doesn't lose sync, in fact if I
didn't monitor the stats I'd probably not know it happens.


Well, mine is fluctuating wildly (from anywhere between 12 to 26)
polled every 5 seconds.

OK, that is a significant difference from what you posted
previously, it sounds like there is either a line fault or a
continuous source of impulsive noise.


I've also been having problems with voice calls as well as ADSL
loss of synch. 3 BT engineers in a few days have given their
opinions. The first 2 explained that new cable would have to be
laid (because of low insulation on the existing cable) but as this
would be an expensive job another engineer may be asked to give an
opinion. Sure enough he did and found another pair of copper wires
coming in to the house which he duly connected. This seems to have
solved the voice call problem but not the ADSL problem and the
line noise is now fluctuating wildly.

Right, so has the 3rd engineer simply changed the local drop cable
over? If so then the connection to the exchange from the nearest
junction cabinet may be the problem, hence the comments of the first
two engineers.


Which is completely the wrong practice as if the cable is going
faulty it _WILL_ affect all pairs, which (if I'm reading between the
lines correctly) is UG anyway (hence the costs in getting it
changed). Keep reporting the fault, it sounds like you've had 2 honest
engineers & 1 FRS points chaser, can't help but wonder what the
first 2 did about the problem though...


Thanks Brian and Kraftee.

Kraftee, you are spot on. Yes the cable is underground and all
engineers explained that the cost of having it replaced (including
digging) would lead to *all* other options being exhausted. The
option that was chosen was to use a spare pair coming in to the home
from a box about 40 metres away (and one that was presumably provided
so that an extra line could be provided if needed)

The second engineer even asked me to sign a form giving permission for
digging on a small area of grass outside the home so that the
underground cable could be replaced. The first engineer explained
that there wasn't much point swapping pairs because the cable itself
was faulty. Because it was an intermittent fault however even the
first faulty tested pair wasn't always showing a fault.

Now I'm buggered though: whilst the downstream attenuation has
dropped by 2db the chaotic line noise margin is such that a 2Mbps
service will be out of the question (but it does seem to be
supporting a 1Mbps service). Can't complain too much I suppose.

Gareth.


Well you could if it was affecting your voice calls (lirttle hint for you
there)....


 




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