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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.

ADSL Max target SNR oddities



 
 
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  #1  
Old November 17th 08, 12:11 PM posted to uk.telecom.broadband
John Livingston
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Posts: 31
Default ADSL Max target SNR oddities

Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here.
Dead stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs
(rather than a noise/error threshold failure). Or is it my router which
is requesting the high SNR target ? (Draytek 2800VG).

John
  #2  
Old November 17th 08, 12:52 PM posted to uk.telecom.broadband
Peter Crosland
external usenet poster
 
Posts: 1,463
Default ADSL Max target SNR oddities

Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here. Dead
stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs (rather
than a noise/error threshold failure). Or is it my router which is
requesting the high SNR target ? (Draytek 2800VG).



I have had similar problems with the Draytek range. It seems that Draytek
have skewed their algorithm quite a lot in favour of stability rather than
speed. Having favoured Draytek for years I have given them up and switched
to 2Wire 2700HGs that are badged as BT Business hubs and are often available
on eBay for less than 20. Unless you need some of the more esoteric
facilities of the Draytek then the win hands down in stability and speed.

Peter Crosland


  #3  
Old November 17th 08, 12:53 PM posted to uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 1,000
Default ADSL Max target SNR oddities

John Livingston wrote:
Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here.
Dead stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs
(rather than a noise/error threshold failure). Or is it my router which
is requesting the high SNR target ? (Draytek 2800VG).

John

Seriously dunno..

Any idea what your BRAS is?

  #4  
Old November 17th 08, 01:48 PM posted to uk.telecom.broadband
John Livingston
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Posts: 31
Default ADSL Max target SNR oddities

The Natural Philosopher wrote:

Seriously dunno..

Any idea what your BRAS is?

Steady at 2Mb.

John
  #5  
Old November 17th 08, 02:17 PM posted to uk.telecom.broadband
Graham J
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Posts: 389
Default ADSL Max target SNR oddities


"Peter Crosland" wrote in message
et...
Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here.
Dead stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs
(rather than a noise/error threshold failure). Or is it my router which
is requesting the high SNR target ? (Draytek 2800VG).



I have had similar problems with the Draytek range. It seems that Draytek
have skewed their algorithm quite a lot in favour of stability rather than
speed. Having favoured Draytek for years I have given them up and switched
to 2Wire 2700HGs that are badged as BT Business hubs and are often
available on eBay for less than 20. Unless you need some of the more
esoteric facilities of the Draytek then the win hands down in stability
and speed.


Certainly the older Vigor routers (2600 etc) give better performance on poor
or long lines.

As a compromise I use a Vigor ethernet router (a 2910) configured for PPPoE
connected to a cheap Edimax router configured in bridge mode (i.e. as an
ethernet modem) This gives the functionality I require (multiple LAN-LAN
VPNs) together with good sync speed and nominal 6dB SNR margin. I also have
two separate phone lines, each with an ADSL service, therefore two Edimax
routers and the Vigor configured for load balancing.

--
Graham J


  #6  
Old November 17th 08, 02:44 PM posted to uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 1,000
Default ADSL Max target SNR oddities

John Livingston wrote:
The Natural Philosopher wrote:

Seriously dunno..

Any idea what your BRAS is?

Steady at 2Mb.

John

Well in which case, its not going to gain you anything by getting a
better synch rate.

Unless you can force it to consistently synch 2.5Mbps.

You may be able to tweak the router to go for better speeds.
  #7  
Old November 17th 08, 03:22 PM posted to uk.telecom.broadband
Ato_Zee
external usenet poster
 
Posts: 343
Default ADSL Max target SNR oddities


Certainly the older Vigor routers (2600 etc) give better performance on
poor
or long lines.


That was my experience with the Vigor (non-wireless) 2600.
The long line flash seemed to lift the high frequency gain,
it said attenuation was lower, which it can't be, it was
because the higher gain gave more signal, which it interpreted
as a lower loss. It was ADSL only.
Found a BT Voyager 240 (non-wireless) for a tenner on eBay
(local no postage) it is ADSL+. Faster than the Vigor 2600,
and importantly DMT tool compatible. Setting a lower
target SNR made it much faster.
For a similar figure got a (wireless) WAG54GS and, with a
bit of arm twisting, got the DMT tool compatible flash.
With lower target SNR performs a bit faster than the
Voyager 240.
I've gone from 2.528Mbps to 4.768Mbps (stable no
resyncs) can push it a bit faster by lowering the target
SNR, but, though it syncs faster it falls back during the
next day to 4.768, so I guess that's as good as I'll get.
What I've deduced from experimenting is:-
Default target SNR is around 12db
Too many loss of carrier and restarts are interpreted
as an unstable line and penalised, taking 2 weeks
(or more) to come back up to speed.
Assuming no loss of carrier the DSLAM algorithm
tracks CRC errors, if they stay consistently low
for several days it will cautiously lower the target
SNR of its own accord. If a reduction of target
SNR is immenent the DSLAM responds to DMT
tools attempt to lower the target SNR.
Keep using DMT tool too often to lower SNR margin
is interpreted as an unstable line and penalised.
Used cautiously DMT tool will get the best you can
out of the line you've got, tell you a lot about
you short and long term CRC's, as well a plot
your SNR (useful if you have bursts of noise,
you can see them).
  #8  
Old November 17th 08, 09:39 PM posted to uk.telecom.broadband
Eeyore
external usenet poster
 
Posts: 3,222
Default ADSL Max target SNR oddities



John Livingston wrote:

Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here.
Dead stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs
(rather than a noise/error threshold failure). Or is it my router which
is requesting the high SNR target ? (Draytek 2800VG).


Do you have a decent ISP that has people who speak competent English and
understand what you're talking about ? Get them to check with BT. They CAN
fiddle with this stuff.

Graham

  #9  
Old November 17th 08, 09:40 PM posted to uk.telecom.broadband
Eeyore
external usenet poster
 
Posts: 3,222
Default ADSL Max target SNR oddities



Peter Crosland wrote:

Could someone try this and confirm what I have been seeing ?

Normal target SNR on resync - 10dB (has been for ages).
Stable line - resyncs once or twice a week. Speeds around 2.5-2.8Mb

OK - here we go. Switch off router for a couple of minutes.
Switch on again.
Resyncs at target SNR of 14dB(!!). This is consistent - not a one-off.
Speed is of course WAY down. If I don't intervene, it will stay here. Dead
stable, but slow.

Force a resync from the router command line - resyncs at normal 10dB.

It looks a bit like BT Wholesale has set the DSLAM to resync at a much
higher target SNR than usual when a complete loss of signal occurs (rather
than a noise/error threshold failure). Or is it my router which is
requesting the high SNR target ? (Draytek 2800VG).


I have had similar problems with the Draytek range. It seems that Draytek
have skewed their algorithm quite a lot in favour of stability rather than
speed. Having favoured Draytek for years I have given them up and switched
to 2Wire 2700HGs that are badged as BT Business hubs and are often available
on eBay for less than 20. Unless you need some of the more esoteric
facilities of the Draytek then the win hands down in stability and speed.


My Origo router holds the line with under 4 dB SNR margin !

Graham

  #10  
Old November 17th 08, 09:42 PM posted to uk.telecom.broadband
Eeyore
external usenet poster
 
Posts: 3,222
Default ADSL Max target SNR oddities



Graham J wrote:

I also have two separate phone lines, each with an ADSL service, therefore two
Edimax
routers and the Vigor configured for load balancing.


Interesting. How easy is that to set up ?

Graham

 




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