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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.

DB losses and speeds...



 
 
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  #1  
Old April 4th 06, 11:20 AM posted to uk.telecom.broadband
Doz
external usenet poster
 
Posts: 75
Default DB losses and speeds...

Hi all,

Is there a list of db losses and speeds possible with those losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?
  #2  
Old April 4th 06, 05:49 PM posted to uk.telecom.broadband
kraftee
external usenet poster
 
Posts: 1,069
Default DB losses and speeds...

Doz wrote:
Hi all,

Is there a list of db losses and speeds possible with those losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?


Rather late in the game aren't you, when/if ADSLMAX rolls out on your
line it will test your line for what it can handle which could be
completely different to someone else's with the same loss


  #3  
Old April 4th 06, 11:19 PM posted to uk.telecom.broadband
Doz
external usenet poster
 
Posts: 75
Default DB losses and speeds...

On Tue, 4 Apr 2006 17:49:41 +0100, kráftéé wrote:

Doz wrote:
Hi all,

Is there a list of db losses and speeds possible with those losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?


Rather late in the game aren't you, when/if ADSLMAX rolls out on your
line it will test your line for what it can handle which could be
completely different to someone else's with the same loss


what kind of ****ed up answer is that ?
  #4  
Old April 4th 06, 11:55 PM posted to uk.telecom.broadband
kraftee
external usenet poster
 
Posts: 1,069
Default DB losses and speeds...

Doz wrote:
On Tue, 4 Apr 2006 17:49:41 +0100, kráftéé wrote:

Doz wrote:
Hi all,

Is there a list of db losses and speeds possible with those
losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?


Rather late in the game aren't you, when/if ADSLMAX rolls out on
your line it will test your line for what it can handle which
could be completely different to someone else's with the same loss


what kind of ****ed up answer is that ?


Exactly what it says, there is no list of dB losses & speeds, each
line will be taken on it's on merits & the monitoring equipment will
automatically come to a conclusion about what speed it will allow &
whether the service will be interleaved or not. Still trying to get
my head around how they are going to change the SNR from the equipment
end but the breifing I received today stated that it is possible
(probably by dropping the speed but we shall see in the fulness of
time, which will be around 10days or so)...


  #5  
Old April 5th 06, 08:28 AM posted to uk.telecom.broadband
Doz
external usenet poster
 
Posts: 75
Default DB losses and speeds...

On Tue, 4 Apr 2006 23:55:35 +0100, kráftéé wrote:

Doz wrote:
On Tue, 4 Apr 2006 17:49:41 +0100, kráftéé wrote:

Doz wrote:
Hi all,

Is there a list of db losses and speeds possible with those
losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?

Rather late in the game aren't you, when/if ADSLMAX rolls out on
your line it will test your line for what it can handle which
could be completely different to someone else's with the same loss


what kind of ****ed up answer is that ?


Exactly what it says, there is no list of dB losses & speeds, each
line will be taken on it's on merits & the monitoring equipment will
automatically come to a conclusion about what speed it will allow &
whether the service will be interleaved or not. Still trying to get
my head around how they are going to change the SNR from the equipment
end but the breifing I received today stated that it is possible
(probably by dropping the speed but we shall see in the fulness of
time, which will be around 10days or so)...


Yes.. but...

What is taken into account when deciding the line speed ? Surely it's just loss
and noise ? Essentially the SNR.

What else could be taken into consideration ? Line length is not an issue as
this affects the SNR. Copper or Alu.. same again.. SNR.

Currently, BT use a SNR to speed ratio type of thing... certain SNR will run a
certain speed. So having a very lossy line (same as being a long way from exch)
would be reduced speed. And this would also be true if you had a ****ty
aluminium line and were right next to the exchange... the SNR would suck.

Any ideas what leel of snr will be acceptable to run a certain speed ?
  #6  
Old April 5th 06, 09:59 AM posted to uk.telecom.broadband
poster
external usenet poster
 
Posts: 1,542
Default DB losses and speeds...

On Wed, 5 Apr 2006 08:28:39 +0100, Doz wrote:

Yes.. but...

What is taken into account when deciding the line speed ? Surely it's just loss
and noise ? Essentially the SNR.


Go back and look at some posts over the last month/two from Alan Flavell,
where he explains what happened when he was on the DSL Max trial (he's in
Glasgow on one of the exchanges which was updated early). He said only in
the last 24 hours that the exchange tried to provide 7 Mbps but that wasn't
stable and it caused disconnectsion/re-sync until it settled at a speed just
below 6 Mbps. So error rates and so on can be part of the criteria. So the
simple attenuation / SNR figures are not "magic numbers" which equate to any
specific speed, just a range (the BT Broadband checker suggests my line will
be capable of "5.5Mbps up to 8Mbps" but also says "potential" so they're not
guaranteeing anything more than a chance of that range of speeds (and given
the speed mentioned by Alan, with a loss of around 33db, mine at ~35db may
easily be below his speed...

A friend on Bulldog is getting data at 6.5+ Mbps with sync speed of around
7.2 Mbps but he lives much closer (will guess at 5 minutes walk (and that's
because there's no direct route to walk - about 3-400 metres), compared with
a 20+ minute walk from my area into the centre of town. Peter M.

--
A few GB a month (at up to 8000 kbps) for 14.99 ? Yes!
See http://tinyurl.com/5jpa4 I'm happy to save cash!
  #7  
Old April 5th 06, 07:44 PM posted to uk.telecom.broadband
kraftee
external usenet poster
 
Posts: 1,069
Default DB losses and speeds...

Doz wrote:
On Tue, 4 Apr 2006 23:55:35 +0100, kráftéé wrote:

Doz wrote:
On Tue, 4 Apr 2006 17:49:41 +0100, kráftéé wrote:

Doz wrote:
Hi all,

Is there a list of db losses and speeds possible with those
losses ?

Would be very handy to have that sort of info...

eg: a certain loss "could" support a certain speed... ?

Rather late in the game aren't you, when/if ADSLMAX rolls out on
your line it will test your line for what it can handle which
could be completely different to someone else's with the same
loss

what kind of ****ed up answer is that ?


Exactly what it says, there is no list of dB losses & speeds, each
line will be taken on it's on merits & the monitoring equipment
will automatically come to a conclusion about what speed it will
allow & whether the service will be interleaved or not. Still
trying to get my head around how they are going to change the SNR
from the equipment end but the breifing I received today stated
that it is possible (probably by dropping the speed but we shall
see in the fulness of time, which will be around 10days or so)...


Yes.. but...

What is taken into account when deciding the line speed ? Surely
it's just loss and noise ? Essentially the SNR.

What else could be taken into consideration ? Line length is not an
issue as this affects the SNR. Copper or Alu.. same again.. SNR.

Currently, BT use a SNR to speed ratio type of thing... certain
SNR will run a certain speed. So having a very lossy line (same as
being a long way from exch) would be reduced speed. And this would
also be true if you had a ****ty aluminium line and were right next
to the exchange... the SNR would suck.


You are getting your terminology wrong what you are talking about is
loop loss not SNR.

Any ideas what leel of snr will be acceptable to run a certain
speed ?


NO SNR does not equate to speed levels it's primarily loop loss which
does, but as of the begining of the week all the old tables/guess work
etc has been thrown to the wind as it will be done by machine, on a
line by line basis, taking into consideration both loss, SNR and also
interleaving as well. There will be no guessing as the machine will
monitor the line to see the lowest stable connection speed, over a
period of 10 days, & then make up it's mind what it is going to give
you & there won't be anything you can do, other than find an ISP which
isn't going to use MaxDSL.

If you want the old tables, it was below 43dB loss for 2Mb, below 60dB
for 1Mb & above 60dB for 512 or 256, anything in double figures or
high single figures for the SNR was ok.

See there isn't a corelation between SNR & speeds & BT have never done
so.


  #8  
Old April 6th 06, 12:31 PM posted to uk.telecom.broadband
Alan J. Flavell
external usenet poster
 
Posts: 126
Default DB losses and speeds...

On Wed, 5 Apr 2006, poster wrote:

Go back and look at some posts over the last month/two from Alan
Flavell, where he explains what happened when he was on the DSL Max
trial (he's in Glasgow on one of the exchanges which was updated
early). He said only in the last 24 hours that the exchange tried
to provide 7 Mbps but that wasn't stable and it caused
disconnectsion/re-sync until it settled at a speed just below 6
Mbps.


Just to clarify this, in case anyone mis-interprets what you wrote -
yes, I *said* it "in the last 24 hours" of your posting, *but* I was
referring to the period of 10 days following the upgrading to Max.

Once that period was over, it's been pretty stable, with only small
adjustments being observed to the line speed (I don't watch it
continuously, so I've no idea how often it's getting twiddled, I just
note slightly different values when I look at it). Maybe I'll
implement SNMP logging (the router seems to offer it), and then maybe
it would tell me about such changes, but I'm not really that fussed
about it.

So error rates and so on can be part of the criteria. So the simple
attenuation / SNR figures are not "magic numbers" which equate to
any specific speed, just a range


Fair comment, but see http://212.23.23.177/calc.htm

As a matter of interest, I tried feeding some pre-Max values into the
calculator and comparing its estimate with my actual post-Max results.

The calculator refers to "Downstream" attenuation and noise margin
figures: my router refers to "Local" and "Remote" values instead. I
presume that the values I needed to use were the "Local" ones?

Feeding in some pre-Max values of 2M, attenuation of 31.5, and SNR
margin of 20, the calculator got an estimate of 6619k.

Which is slightly optimistic, but close enough to what I'm getting
for it to be a useful prediction.

(Those numbers were just one snapshot - you might see me quoting
slightly different snapshot figures in other postings.)

(and given the speed mentioned by Alan, with a loss of around 33db,
mine at ~35db may easily be below his speed...


It depends also on your noise margin. As indeed that cited calculator
takes into account.

The other difference is that, previously, BT would make a conservative
choice of one fixed speed (2M, 1M, 512k...) which they considered to
be "safe" based on a set of readings. Now, the Max engine is
adjusting the speed in much smaller increments, to optimise what it
can get out of the line. It stands to reason that the results are
likely to be faster in the majority of cases - but they should also
adapt better to changing line quality, for those who suffer from such
effects.

h t h
  #9  
Old April 6th 06, 01:27 PM posted to uk.telecom.broadband
poster
external usenet poster
 
Posts: 1,542
Default DB losses and speeds...

On 6 Apr 2006 12:31 "Alan J. Flavell" wrote:

Just to clarify this, in case anyone mis-interprets what you wrote -
yes, I *said* it "in the last 24 hours" of your posting, *but* I was
referring to the period of 10 days following the upgrading to Max.


yes I could have phrased that less ambiguously - "he posted within the
last 24 hours about his regrade some time ago"... perhaps.


Fair comment, but see http://212.23.23.177/calc.htm


No thanks. I'm happy enough to wait and see.


--
A few GB a month (at up to 8000 kbps) for 14.99 ? Yes!
See http://tinyurl.com/5jpa4 I'm happy to save cash!
  #10  
Old April 6th 06, 04:32 PM posted to uk.telecom.broadband
Alan J. Flavell
external usenet poster
 
Posts: 126
Default DB losses and speeds...

On Wed, 5 Apr 2006, kráftéé and MISSINGkrafteeTERMINATOR wrote:

[...]
If you want the old tables, it was below 43dB loss for 2Mb, below
60dB for 1Mb & above 60dB for 512 or 256, anything in double figures
or high single figures for the SNR was ok.

See there isn't a corelation between SNR & speeds & BT have never
done so.


You may very well be correct in saying BT didn't *use* the SNR figure
in making their estimate of the speed that they were willing to try on
a line. Pre-Max, they would have to make their estimate based on
figures which they could read-off without having an ADSL router at the
far end, after all; so presumably the loop loss was something that
could be measured from their end without needing anything at the sub's
end.

But the speed and the SNR most certainly -are- related to each other:
as the speed is raised, on an otherwise given line, the SNR goes down,
until, beyond about 5 - 7 dB SNR, the line becomes unusable, and that
sets the max speed.

For example, before Max-ing, I had 20 - 22dB local SNR at 2Mbit,
whereas I've now got a bit short of 6Mbit with 5 - 7 dB SNR remaining.

Quite what basis the Max engine uses for deciding on the optimum
speed, I don't know (maybe your briefings have covered that, and you
can tell us?), but, as I say, when it's reached its target, it seems
that the local SNR reading on the ADSL router is around 5 - 7dB.

regards
 




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