SNR Margin changed from 6dB to 12dB on ADSL Max

Hi,

I have had Max for about 4 months, been working very well, I could hold
around 6Mb/s sync with SNR margin down to 5 or 6 dB at times. The
attenuation is 45dB and constant as it should be. Download speed was
just over 5 Mb/s, all was going well.

The problem now is my SNR Margin has jumped to at least 12dB when I
reconnect (it used to be 6dB) and this has killed my sync speed and as a
result of that also my download speed.

I assume that it's the exchange equipment that has done this, as I have
tried a different router and it's the same high SNR Margin (12dB).

Prior to this problem I did have some random tripping of my house RCCB
for a week or so (now fixed), would that have made the exchange think I
have a bad connection as my router is not on my UPS (as I have moved it
to the master socket)?

If that is the problem will it improve and be changed back to the lower
SNR Margin automatically now my connection is not dropping due to power
cuts. Or could the problem be something else?

Many thanks for any thoughts,
--
Paul

Paul wrote:

> I have had Max for about 4 months, been working very well, I could hold
> around 6Mb/s sync with SNR margin down to 5 or 6 dB at times. The
> attenuation is 45dB and constant as it should be. Download speed was
> just over 5 Mb/s, all was going well.

What was the attenuation? Has it changed recently?

> The problem now is my SNR Margin has jumped to at least 12dB when I
> reconnect (it used to be 6dB) and this has killed my sync speed and as a
> result of that also my download speed.

The margin is the difference between the minimum signal level you need
for a given sync speed, and what you currently have. So the bigger the
difference, the better. [lightbulb goes on in alexd's head] So I expect
what has happened is that you've been dropped to a lower sync speed, in
an attempt by the DSLAM to get you a more reliable connection. So, the
minimum signal you need for the speed you are currently on is lower
than the previous speed you were on, but the actual signal strength
hasn't changed. Hence, your margin doubles, and you have a slower but
theoretically more reliable connection. All makes sense when you think
about it.

> I assume that it's the exchange equipment that has done this, as I have
> tried a different router and it's the same high SNR Margin (12dB).

Yep.

> Prior to this problem I did have some random tripping of my house RCCB
> for a week or so (now fixed), would that have made the exchange think I
> have a bad connection as my router is not on my UPS (as I have moved it
> to the master socket)?
>
> If that is the problem will it improve and be changed back to the lower
> SNR Margin automatically now my connection is not dropping due to power
> cuts.

Hopefully.

> Or could the problem be something else?

The problem could be something else. Unplugged that ancient fax machine
that was injecting horrific quantities RF noise into the line, from
it's faulty switched-mode PSU?


A sidenote: Some people question the veracity of any of the noise- and
signal-related figures given by economically-made routers from the Far
East, citing lack of calibration and whatnot; the suggestion is often
made that only data from properly calibrated E-side kit can be taken
with any degree of seriousity. If that's the case, it would be nice to
be able for the consumer to see live data from the DSLAM [or wherever
the stats come from] they're connected to. Perhaps any port 80 HTTP
requests to the IP address of my-line-stats.bt.net could be intercepted
by exchange equipment, with the requisite info delivered on an HTML
page. Of course, it would only be of any interest to geeks like me, so
it's not likely it's ever going to happen. Oh well, life goes on.

alexd

Paul <me@[127.0.0.1]> wrote:

>I assume that it's the exchange equipment that has done this, as I have
>tried a different router and it's the same high SNR Margin (12dB).

>Prior to this problem I did have some random tripping of my house RCCB
>for a week or so (now fixed), would that have made the exchange think I
>have a bad connection as my router is not on my UPS (as I have moved it
>to the master socket)?

If the exchange sees your connection drop frequently (I remember reading
something about 10 times in an hour but I don't know what the actual
threshold and rules are) it assumes you have a unstable connection and will
increase the SNR margin it tells your modem to sync with by 3db. If it
continues to think the connection is unstable it will do it again.

>If that is the problem will it improve and be changed back to the lower
>SNR Margin automatically now my connection is not dropping due to power
>cuts.

I read it is quite difficult to get BT to lower an SNR margin which has
been increased. All you can do is ask your ISP to ask BT to do it - explain
the situation. I also read an increased SNR margin will be decreased by 3db
automatically after 14 days of uninterrupted connection. I have also read
than after no connection for 14 days (got a holiday coming up?) the
exchange will start from again scratch with a 10 day training period like
when you first got the ADSL Max service.

I don't know for sure any of the above is true.
--

In message <(E-Mail Removed). com>,
ale.cx <(E-Mail Removed)> writes
>
>Paul wrote:
>
>> I have had Max for about 4 months, been working very well, I could hold
>> around 6Mb/s sync with SNR margin down to 5 or 6 dB at times. The
>> attenuation is 45dB and constant as it should be. Download speed was
>> just over 5 Mb/s, all was going well.
>
>What was the attenuation? Has it changed recently?

No still the same.
>
>> The problem now is my SNR Margin has jumped to at least 12dB when I
>> reconnect (it used to be 6dB) and this has killed my sync speed and as a
>> result of that also my download speed.
>
>The margin is the difference between the minimum signal level you need
>for a given sync speed, and what you currently have. So the bigger the
>difference, the better. [lightbulb goes on in alexd's head] So I expect
>what has happened is that you've been dropped to a lower sync speed, in
>an attempt by the DSLAM to get you a more reliable connection. So, the
>minimum signal you need for the speed you are currently on is lower
>than the previous speed you were on, but the actual signal strength
>hasn't changed. Hence, your margin doubles, and you have a slower but
>theoretically more reliable connection. All makes sense when you think
>about it.

I see how that works, though my connection seemed OK before, download
speed at 5Mb/s and online gaming no problems, (low ping no packet loss).
>
>> I assume that it's the exchange equipment that has done this, as I have
>> tried a different router and it's the same high SNR Margin (12dB).
>
>Yep.
>
>> Prior to this problem I did have some random tripping of my house RCCB
>> for a week or so (now fixed), would that have made the exchange think I
>> have a bad connection as my router is not on my UPS (as I have moved it
>> to the master socket)?
>>
>> If that is the problem will it improve and be changed back to the lower
>> SNR Margin automatically now my connection is not dropping due to power
>> cuts.
>
>Hopefully.

Here's hoping then
>
>> Or could the problem be something else?
>
>The problem could be something else. Unplugged that ancient fax machine
>that was injecting horrific quantities RF noise into the line, from
>it's faulty switched-mode PSU?

Good point I will have to have a listen and check that out, off to find
MW radio and HF receiver.
>
>
>A sidenote: Some people question the veracity of any of the noise- and
>signal-related figures given by economically-made routers from the Far
>East, citing lack of calibration and whatnot; the suggestion is often
>made that only data from properly calibrated E-side kit can be taken
>with any degree of seriousity. If that's the case, it would be nice to
>be able for the consumer to see live data from the DSLAM [or wherever
>the stats come from] they're connected to. Perhaps any port 80 HTTP
>requests to the IP address of my-line-stats.bt.net could be intercepted
>by exchange equipment, with the requisite info delivered on an HTML
>page. Of course, it would only be of any interest to geeks like me, so
>it's not likely it's ever going to happen. Oh well, life goes on.

That would be very useful for fault finding, certainly more accurate
than the router. My router by the way is a Netgear 834pn and have been
plotting the stats with the RouterStats program.
>
>alexd
>
Cheers thanks for the reply
--
Paul

In message <(E-Mail Removed)>, nospam
<(E-Mail Removed)> writes
>Paul <me@[127.0.0.1]> wrote:
>
>>I assume that it's the exchange equipment that has done this, as I have
>>tried a different router and it's the same high SNR Margin (12dB).
>
>>Prior to this problem I did have some random tripping of my house RCCB
>>for a week or so (now fixed), would that have made the exchange think I
>>have a bad connection as my router is not on my UPS (as I have moved it
>>to the master socket)?
>
>If the exchange sees your connection drop frequently (I remember reading
>something about 10 times in an hour but I don't know what the actual
>threshold and rules are) it assumes you have a unstable connection and will
>increase the SNR margin it tells your modem to sync with by 3db. If it
>continues to think the connection is unstable it will do it again.
>
It didn't drop that many times in an hour so maybe it was something else
that caused it and it seemed to jump from 6dB to 12dB but it was over
the new year period so don't know if I noticed it straight away.

>>If that is the problem will it improve and be changed back to the lower
>>SNR Margin automatically now my connection is not dropping due to power
>>cuts.
>
>I read it is quite difficult to get BT to lower an SNR margin which has
>been increased. All you can do is ask your ISP to ask BT to do it - explain
>the situation. I also read an increased SNR margin will be decreased by 3db
>automatically after 14 days of uninterrupted connection. I have also read
>than after no connection for 14 days (got a holiday coming up?) the
>exchange will start from again scratch with a 10 day training period like
>when you first got the ADSL Max service.
>
>I don't know for sure any of the above is true.

I hope it improves after 14 days then, I have about a week left to see
if that's true. Here's hoping, though I suppose I could try and get my
ISP to have the BRAS profile reset (if that's what it's called)
Cheers,
--
Paul

Paul <me@[127.0.0.1]> wrote:

>I hope it improves after 14 days then, I have about a week left to see
>if that's true.

It has to be 14 days continuous which is quite a tall order. My ADSL has
never gone more than 5 days without re-sync but that's probably a modem
issue.

Also you won't know it has changed without disconnecting and seeing if it
syncs with less SNR.

>Here's hoping, though I suppose I could try and get my
>ISP to have the BRAS profile reset (if that's what it's called)

The target SNR set by the exchange is nothing to do with BRAS profiles.
--

ale.cx wrote:

> A sidenote: Some people question the veracity of any of the noise- and
> signal-related figures given by economically-made routers from the Far
> East, citing lack of calibration and whatnot; the suggestion is often
> made that only data from properly calibrated E-side kit can be taken
> with any degree of seriousity. If that's the case, it would be nice to
> be able for the consumer to see live data from the DSLAM [or wherever
> the stats come from] they're connected to. Perhaps any port 80 HTTP
> requests to the IP address of my-line-stats.bt.net could be intercepted
> by exchange equipment, with the requisite info delivered on an HTML
> page. Of course, it would only be of any interest to geeks like me, so
> it's not likely it's ever going to happen. Oh well, life goes on.

I don't think the dslam can measure anything at your end as such.

In the case of upstream margin/errors it already does communicate them
to you, just as your kit may communicate your near errors/margin to it.

Modems/dslams can change the number of bits per channel (same total
bits) without resyncing in response to changing noise.

Andy.

Paul wrote:

> I hope it improves after 14 days then, I have about a week left to see
> if that's true. Here's hoping, though I suppose I could try and get my
> ISP to have the BRAS profile reset (if that's what it's called)

The BRAS is the maximum data speed that will be sent to your line from
the ISP - ensuring that there's not too much congestion at the DSLAM by
everyone getting too much data from the ISPs which the lines cannot cope
with.

(At least, that's how I understand it.)

Anyway, if you ask them to lower the SNR rating back to 6dB they should
know what you're talking about.

Geoff