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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.

Line length / line attenuation correlation query.



 
 
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  #1  
Old November 10th 10, 02:00 AM posted to uk.telecom.broadband
Flyig u 210 +
external usenet poster
 
Posts: 45
Default Line length / line attenuation correlation query.

I've always thought that as the line length increases then so does the line
attenuation, but not necessarily linearly. However I don't understand why
it is that the upstream line attenuation should be so much less than the
downstream line attenuation since line length must be the same, indeed I
would have thought that the same cables were used for both. I know there
must be a simple explanation, but as I don't seem to be able to understand
this, could someone please explain it in simple terms.

Also, is there a way that I can find out what my actual line length is. I
know in the dim and distant past that a dialling a certain number would lead
to a test being carried out to tell you, but I believe that facility no
longer exists

In my case I believe that the line length is around 2.5 km and my downstream
attenuation is 44.1 dB but upstream attenuation is 23.6 dB. Currently on
ADSL2+ I am synching at 7667 kbps with an SNR that varies from around 9.8 dB
during the day but this drops to low values of around 4.5 dB overnight.
Strangely when connected to ADSL just over a month ago I was synching at
7617 kbps with similar values of line attenuation and SNR so don't appear to
have any benefit in speed for the change to ADSL2+ although my ISP estimated
that I should be getting around 13 Mbps. Does this seem to be as it should
be?
--
Heard melodies are sweet, but those Unheard are sweeter
FN 21 +, Mungo Brandybuck of Buckland


  #2  
Old November 10th 10, 02:35 AM posted to uk.telecom.broadband
Denis McMahon
external usenet poster
 
Posts: 50
Default Line length / line attenuation correlation query.

On 10/11/10 01:00, Flyig u 210 + wrote:

I've always thought that as the line length increases then so does the line
attenuation, but not necessarily linearly. However I don't understand why
it is that the upstream line attenuation should be so much less than the
downstream line attenuation since line length must be the same, indeed I
would have thought that the same cables were used for both.


Upstream users lower frequencies than downstream. The cable is more
efficient at carrying these lower frequencies. Hence less upstream
attenuation.

Rgds

Denis McMahon

  #3  
Old November 10th 10, 02:42 AM posted to uk.telecom.broadband
nospam
external usenet poster
 
Posts: 82
Default Line length / line attenuation correlation query.

"Flyig u 210 +" wrote:

I've always thought that as the line length increases then so does the line
attenuation, but not necessarily linearly. However I don't understand why
it is that the upstream line attenuation should be so much less than the
downstream line attenuation since line length must be the same


Attenuation due to line capacitance increases with frequency and the
upstream uses the lowest frequencies.

The reported attenuation is the average of the frequencies in use.
  #4  
Old November 10th 10, 04:39 AM posted to uk.telecom.broadband
Mike Tomlinson
external usenet poster
 
Posts: 285
Default Line length / line attenuation correlation query.

In article , Flyig u 210 +
writes

In my case I believe that the line length is around 2.5 km


About the same as mine.

and my downstream
attenuation is 44.1 dB but upstream attenuation is 23.6 dB.


D:23 U:14

Currently on
ADSL2+ I am synching at 7667 kbps with an SNR that varies from around 9.8 dB
during the day but this drops to low values of around 4.5 dB overnight.


Street lighting? Overhead drop from pole?

SNR here is pretty consistent at 9.9-10.0 dB. If I power cycle the
router it usually starts off at about 12 but settles down to 9.9/10.

Strangely when connected to ADSL just over a month ago I was synching at
7617 kbps with similar values of line attenuation and SNR


Think you were doing OK there. Did you try disconnecting any extension
wiring and connecting to the test socket?

so don't appear to
have any benefit in speed for the change to ADSL2+ although my ISP estimated
that I should be getting around 13 Mbps. Does this seem to be as it should
be?


Run DMT (http://dmt.mhilfe.de) on your router and put a screenshot up
somewhere so we can take a look at the SNR (dB per tone) graph. Do two,
one for when you have 9.8dB SNR and another for when it falls to 4.5.

What router are you using?

--
(\__/)
(='.'=)
(")_(")


  #5  
Old November 10th 10, 10:09 AM posted to uk.telecom.broadband
Peter Crosland
external usenet poster
 
Posts: 1,463
Default Line length / line attenuation correlation query.

"Flyig u 210 +" wrote in message
...
I've always thought that as the line length increases then so does the
line attenuation, but not necessarily linearly. However I don't
understand why it is that the upstream line attenuation should be so much
less than the downstream line attenuation since line length must be the
same, indeed I would have thought that the same cables were used for
both. I know there must be a simple explanation, but as I don't seem to
be able to understand this, could someone please explain it in simple
terms.

Also, is there a way that I can find out what my actual line length is.
I know in the dim and distant past that a dialling a certain number would
lead to a test being carried out to tell you, but I believe that facility
no longer exists

In my case I believe that the line length is around 2.5 km and my
downstream attenuation is 44.1 dB but upstream attenuation is 23.6 dB.
Currently on ADSL2+ I am synching at 7667 kbps with an SNR that varies
from around 9.8 dB during the day but this drops to low values of around
4.5 dB overnight. Strangely when connected to ADSL just over a month ago I
was synching at 7617 kbps with similar values of line attenuation and SNR
so don't appear to have any benefit in speed for the change to ADSL2+
although my ISP estimated that I should be getting around 13 Mbps. Does
this seem to be as it should be?


It looks like a straighforward mistake by Plusnet in the estitmation. The
actual line length is not very relevant other than to show an approximate
value for attenuation. The faclity did exist on an earler variant of 17070
but it is no longer available to the public. In any case it was, AFAIK,
always a calcutated value based on the attenuation. A check here

http://www.kitz.co.uk/adsl/max_speed_calc.php

shows that the figures you are getting are very close to the estimate. Given
the line attenuation and noise figures you are not going to get a
significantly higher figure whatever you do. Stop worrying about it!

Peter Crosland


  #6  
Old November 10th 10, 10:59 AM posted to uk.telecom.broadband
Flyig u 210 +
external usenet poster
 
Posts: 45
Default Line length / line attenuation correlation query.

Denis McMahon wrote:
On 10/11/10 01:00, Flyig u 210 + wrote:

I've always thought that as the line length increases then so does
the line attenuation, but not necessarily linearly. However I don't
understand why it is that the upstream line attenuation should be so
much less than the downstream line attenuation since line length
must be the same, indeed I would have thought that the same cables
were used for both.


Upstream users lower frequencies than downstream. The cable is more
efficient at carrying these lower frequencies. Hence less upstream
attenuation.

Rgds

Denis McMahon


Thank you Denis, what frequency range do they use then? High enough to
incur the skin effect we used to talk about in the old days I presume. I
suppose I should have thought of that.
--
Heard melodies are sweet, but those Unheard are sweeter
FN 21 +, Mungo Brandybuck of Buckland


  #7  
Old November 10th 10, 11:08 AM posted to uk.telecom.broadband
Andy Burns
external usenet poster
 
Posts: 486
Default Line length / line attenuation correlation query.

Flyig u 210 + wrote:

what frequency range do they use then?


Depends if you're ADSL, ADSL2 (nobody in the UK?) or ADSL2+

http://en.wikipedia.org/wiki/File:ADSL2_frequencies.png

  #8  
Old November 10th 10, 11:10 AM posted to uk.telecom.broadband
Flyig u 210 +
external usenet poster
 
Posts: 45
Default Line length / line attenuation correlation query.

Mike Tomlinson wrote:
In article , Flyig u 210 +
writes

In my case I believe that the line length is around 2.5 km


About the same as mine.

and my downstream
attenuation is 44.1 dB but upstream attenuation is 23.6 dB.


D:23 U:14

Currently on
ADSL2+ I am synching at 7667 kbps with an SNR that varies from
around 9.8 dB during the day but this drops to low values of around
4.5 dB overnight.


Street lighting? Overhead drop from pole?

And all the other interference around. Medium wave radio transmissions and
the like. The drop in SNR does star a considerable time before the street
lighting comes on so there are definitely other sources involved.

SNR here is pretty consistent at 9.9-10.0 dB. If I power cycle the
router it usually starts off at about 12 but settles down to 9.9/10.

When I poweer off my router then the SNR when I reboot it is around 6 dB so
overnight the drop is down to around 0 dB producing dropped connections and
a resetting of the SNR to around 6 dB at that time. This means that when
the daylight hours arrive the SNR ups to 10 dB or sometimes more.
. .
Strangely when connected to ADSL just over a month ago I was
synching at 7617 kbps with similar values of line attenuation and SNR


Think you were doing OK there. Did you try disconnecting any extension
wiring and connecting to the test socket?

Oh! Yes been through that many times before resulting in Openreach rewiring
my main socket and replacing all the outside cabling to our nearest
telegraph pole which is about 25 feet away. The street cabinet is about 100
feet away from that. I also now have a filtered face plate and the only
other connection is for the 'phone and Sky box. Disconnecting them makes no
difference as far as I can see.

so don't appear to
have any benefit in speed for the change to ADSL2+ although my ISP
estimated that I should be getting around 13 Mbps. Does this seem
to be as it should be?


Run DMT (http://dmt.mhilfe.de) on your router and put a screenshot up
somewhere so we can take a look at the SNR (dB per tone) graph. Do
two, one for when you have 9.8dB SNR and another for when it falls to
4.5.

Is that the bit loading graph?

What router are you using?


2wire-2700HGV
--
Heard melodies are sweet, but those Unheard are sweeter
FN 21 +, Mungo Brandybuck of Buckland


  #9  
Old November 10th 10, 11:13 AM posted to uk.telecom.broadband
Flyig u 210 +
external usenet poster
 
Posts: 45
Default Line length / line attenuation correlation query.

Peter Crosland wrote:
"Flyig u 210 +" wrote in message
...
I've always thought that as the line length increases then so does
the line attenuation, but not necessarily linearly. However I don't
understand why it is that the upstream line attenuation should be so
much less than the downstream line attenuation since line length
must be the same, indeed I would have thought that the same cables
were used for both. I know there must be a simple explanation, but
as I don't seem to be able to understand this, could someone please
explain it in simple terms.

Also, is there a way that I can find out what my actual line length
is. I know in the dim and distant past that a dialling a certain
number would lead to a test being carried out to tell you, but I
believe that facility no longer exists

In my case I believe that the line length is around 2.5 km and my
downstream attenuation is 44.1 dB but upstream attenuation is 23.6
dB. Currently on ADSL2+ I am synching at 7667 kbps with an SNR that
varies from around 9.8 dB during the day but this drops to low
values of around 4.5 dB overnight. Strangely when connected to ADSL just
over a month
ago I was synching at 7617 kbps with similar values of line
attenuation and SNR so don't appear to have any benefit in speed for
the change to ADSL2+ although my ISP estimated that I should be
getting around 13 Mbps. Does this seem to be as it should be?


It looks like a straighforward mistake by Plusnet in the estitmation.
The actual line length is not very relevant other than to show an
approximate value for attenuation. The faclity did exist on an earler
variant of 17070 but it is no longer available to the public. In any
case it was, AFAIK, always a calcutated value based on the
attenuation. A check here
http://www.kitz.co.uk/adsl/max_speed_calc.php

shows that the figures you are getting are very close to the
estimate. Given the line attenuation and noise figures you are not
going to get a significantly higher figure whatever you do. Stop
worrying about it!

Not worried about it Peter, just interested in understanding the workings
of it all, which involve answering little queries that I can't work out for
myself. Call it an enquiring mind. The more I ask, the more information I
get and that leads to a better understanding of it all.
--
Heard melodies are sweet, but those Unheard are sweeter
FN 21 +, Mungo Brandybuck of Buckland


  #10  
Old November 10th 10, 11:24 AM posted to uk.telecom.broadband
Mark
external usenet poster
 
Posts: 525
Default Line length / line attenuation correlation query.

On Wed, 10 Nov 2010 01:00:24 -0000, "Flyig u 210 +"
wrote:

Also, is there a way that I can find out what my actual line length is. I
know in the dim and distant past that a dialling a certain number would lead
to a test being carried out to tell you, but I believe that facility no
longer exists


BT used to tell you your line length but they won't any more.
Presumably to stop people saying "my line length is only X so I should
get better ADSL performance". I believe they only estimated the
length from the downstream attuation figure which you can do via sites
like kitz.
--
(\__/) M.
(='.'=) Due to the amount of spam posted via googlegroups and
(")_(") their inaction to the problem. I am blocking some articles
posted from there. If you wish your postings to be seen by
everyone you will need use a different method of posting.

 




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