Accuracy of BB line checker and DACS

Quick question: ....

Does having a DACS line cause a false positive or incorrect results on the
BB availability checker? The reason I ask is that I've recently had a new BT
line installed, which is only capable of supporting 512k according to the
checker.
According to the checker, my next-door neighbours and houses around mine
/should/ support up to 2Mbits/sec, but these lines are all DACS'ed. I seem
to remember reading somewhere that a DACS line can be better than a standard
analogue line as you have a digital pair from the exchange all the way up to
the pole or your house.... correct? My new line is a true pair (i.e. no
DACS) as I ordered it specifically for BB and told them DACS wasn't allowed


I still intend placing a manual order for 2Mbit, and will see how that goes.
All I know at this stage is that the line is 3.8kms.

Any comments gratefully received.

G


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On Thu, 8 Jul 2004 14:43:18 +0100, Gari P <(E-Mail Removed)> wrote:

> Quick question: ....
>
> Does having a DACS line cause a false positive or incorrect results on
> the
> BB availability checker? The reason I ask is that I've recently had a
> new BT
> line installed, which is only capable of supporting 512k according to the
> checker.
> According to the checker, my next-door neighbours and houses around mine
> /should/ support up to 2Mbits/sec, but these lines are all DACS'ed. I
> seem
> to remember reading somewhere that a DACS line can be better than a
> standard
> analogue line as you have a digital pair from the exchange all the way
> up to
> the pole or your house.... correct? My new line is a true pair (i.e. no
> DACS) as I ordered it specifically for BB and told them DACS wasn't
> allowed
>
>
> I still intend placing a manual order for 2Mbit, and will see how that
> goes.
> All I know at this stage is that the line is 3.8kms.
>
> Any comments gratefully received.
>
> G
>
>
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> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
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>
>

Hi,

It might be the 3.8km distance that is causing the checker to say that you
can only get 512kbps as the distance limit is 3.5km. It's possible that
your neighbour's line takes a different (shorter) route back to the
exchange hence why it says 2Mbps may be possible.
The initial line check is based on historical data and so cannot be 100%
accurate, a DACS on the line generally doesn't make any difference to the
availability checker.
Without placing an order on the line there's no way of being 100% certain
either way. If you did place an order on a line with a DACS then (subject
to cost limits) the DACS would be removed as part of the ADSL activation.

--
Regards,

| Dave Tomlinson Broadband Solutions For
| Technical Support for Home & Business
| PlusNet plc @ http://www.plus.net
+ ----- My Referrals - It pays to recommend PlusNet -----

"PlusNet Support Team" <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...

Thanks for the reply ........

> It might be the 3.8km distance that is causing the checker to say that you
> can only get 512kbps as the distance limit is 3.5km. It's possible that
> your neighbour's line takes a different (shorter) route back to the
> exchange hence why it says 2Mbps may be possible.

Sorry, I forgot to mention the line is in a semi-rural village and all the
lines from the exchange are fed overhead from two large feeder cables (2x 50
pair perhaps?) It is easy to trace the neighbours / surrounding houses cable
routes, and they are all fed from the same DP as my house, and all go down
to the exchange on the large cables. I found it strange that lines further
away from mine were able to receive 2Mbit, yet my new line is 512k only ....
and the presence of DACS on the capable lines. I thought the checker now
measured your line loss / attenuation, not your actual line length?

> The initial line check is based on historical data and so cannot be 100%
> accurate, <snip>

I'm glad you say that, because I've said that for a long time. On my other
line (different house) I have 1Mbit, yet the BT code for this line is AAEA
..
> Without placing an order on the line there's no way of being 100% certain
> either way. If you did place an order on a line with a DACS then (subject
> to cost limits) the DACS would be removed as part of the ADSL activation.

Luckily I don't have DACS on my line (I was insistent to BT about that) ...
but I've known all along I'm borderline for >512k services. The line
currently has a status of RGEZ. I will give it a shot though ....

Cheers,
G


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On Thu, 8 Jul 2004 16:08:01 +0100, Gari P <(E-Mail Removed)> wrote:

> "PlusNet Support Team" <(E-Mail Removed)> wrote in message
> news(E-Mail Removed)...
>
> Thanks for the reply ........

No problem.

>> It might be the 3.8km distance that is causing the checker to say that
>> you
>> can only get 512kbps as the distance limit is 3.5km. It's possible that
>> your neighbour's line takes a different (shorter) route back to the
>> exchange hence why it says 2Mbps may be possible.
>
> Sorry, I forgot to mention the line is in a semi-rural village and all
> the
> lines from the exchange are fed overhead from two large feeder cables
> (2x 50
> pair perhaps?) It is easy to trace the neighbours / surrounding houses
> cable
> routes, and they are all fed from the same DP as my house, and all go
> down
> to the exchange on the large cables. I found it strange that lines
> further
> away from mine were able to receive 2Mbit, yet my new line is 512k only
> ....
> and the presence of DACS on the capable lines. I thought the checker now
> measured your line loss / attenuation, not your actual line length?

It depends when the reading was taken as to what it actually looks at. As
the data is of a historical rather than it doing a live test when you use
the checker it could be based on either a line loss or line length result.
If your neighbour's line takes the same route as your's then you would
have thought they would likely be able to support the same ADSL services
(not always the case but generally right) but if for your line the checker
used line length (3.8km as you said) but your neighbour's it used line
loss (maybe less than 45dB) then that would explain the difference.


<snip>

>
> Luckily I don't have DACS on my line (I was insistent to BT about that)
> ...
> but I've known all along I'm borderline for >512k services. The line
> currently has a status of RGEZ. I will give it a shot though ....
>
> Cheers,
> G

There's no harm in giving it a try, if it does happen to fail it won't
cost anything. Good luck.



--
Regards,

| Dave Tomlinson Broadband Solutions For
| Technical Support for Home & Business
| PlusNet plc @ http://www.plus.net
+ ----- My Referrals - It pays to recommend PlusNet -----

On Thu, 8 Jul 2004 16:08:01 +0100, "Gari P" <(E-Mail Removed)>
wrote:

>yet the BT code for this line is AAEA


AA means "we have no clue"

Phil
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On Thu, 08 Jul 2004 20:28:21 +0100, Phil Thompson
<(E-Mail Removed)> wrote:

>On Thu, 8 Jul 2004 16:08:01 +0100, "Gari P" <(E-Mail Removed)>
>wrote:
>
>>yet the BT code for this line is AAEA
>
>
>AA means "we have no clue"

I thought that was BT.

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In article <(E-Mail Removed)>
Gari P <(E-Mail Removed)> wrote:

>Quick question: ....

>Does having a DACS line cause a false positive or incorrect results on the
>BB availability checker?

No more than usual.

>The reason I ask is that I've recently had a new BT line installed,
>which is only capable of supporting 512k according to the checker.

New lines aren't "tested" for a while after installation, usually 24-48
hours. You may be seeing the result for the previous line with which
your number was associated. Does the SDSL checker have a record for your
number? If not, then you're quite possibly looking at stale data.

>According to the checker, my next-door neighbours and houses around mine
>/should/ support up to 2Mbits/sec, but these lines are all DACS'ed. I seem
>to remember reading somewhere that a DACS line can be better than a standard
>analogue line as you have a digital pair from the exchange all the way up to
>the pole or your house.... correct?

No. With a DACS line there are two analogue connections to the remote
unit, one for each subscriber. There are also two analogue connections
from the exchange unit to the respective line cards. The exchange and
remote units are connected using a single line (the trunk) on which 2B1Q
encoding at 160 kbps is used.

Only trunk between the remote unit near you and the exchange unit near
the line cards is 'digital'. The lines presented to the line card and
your premises are still analogue. Besides regenerating correct line
voltage and ring cadences at the remote end and providing test bus
passthrough, DACS is not much other than two sets of speakers and
microphones at each end that allows two subscribers to use a single pair
back to the exchange without knowing about it.

BT's DSL qualification databases doesn't take account of what service is
being provided on the pair when evaluating its potential suitability for
a DSL service: an line with basic rate ISDN in service on it can still
be indicated as being suitable for DSL providing that the ISDN is
ceased. DACS is an incompatible service, but if you order ADSL, BT will
try to cease it for you. If there are no spare pairs or other people to
DACS when you come to order, you won't be able to have ADSL.

The method used to qualify lines is records-based: the length is used
together with cable diameter and type along with past insertion loss
tests performed in the area to arrive at a result. Needless to say, this
is not always accurate: if no records exist, and the line length can't
be measured, you get the "can't be sure" result.

If you want the 512K service, order now, and you should be successful.

If you want anything faster or a capacity-based charging service, you
need to ascertain whether your line qualification data is stale: if it's
not, get the ISP to place a manual order to ensure that your ADSL
service is provided with the highest possible data rate, so you can flex
up to it later if you want to.

--
James MacDonald

"James MacDonald" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In article <(E-Mail Removed)>
> Gari P <(E-Mail Removed)> wrote:
>
> >Quick question: ....
>
> >Does having a DACS line cause a false positive or incorrect results on
the
> >BB availability checker?
>
> No more than usual.

Good, I was hoping this was the case.

> >The reason I ask is that I've recently had a new BT line installed,
> >which is only capable of supporting 512k according to the checker.
>
> New lines aren't "tested" for a while after installation, usually 24-48
> hours. You may be seeing the result for the previous line with which
> your number was associated.

Ahh .... I've had my line approx 2 months.

>Does the SDSL checker have a record for your
> number? If not, then you're quite possibly looking at stale data.

Yes, it shows the same as the ADSL checker; green for 512k, red for 1 -2
Mbit. All the surrounding lines show amber for 1Mbit and red for 2Mbit SDSL.

<snipped>

Thanks for all the interesting info, I will read over this and take it all
in. Much appreciated.

G


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