IS BT deliberately setting high noise margins to reduce exchangestress?

I ask, because having switched from line A with ISP A, gaily synching at
6dB margin and achieving >4000 synch rates, despite having noise margin
reset LINE B with ISP B, is now on 12dB margin synching reliably at
just over 3000Kbps..This is at the same premises.


The ISP claiming that BT cant, or wont, hardwire my noise margin.

I am wondering if indeed they simply cant supply adequate bandwidth to
the exchange..and this is policy, not technical..

Because the switchback always occurs at precisely 9:30 a.m. Whereas I
would have thought a noise margin reset would have been more or less
when an arbitrary counter gets to a value..

On Sat, 07 Nov 2009 16:18:39 +0000, Dave {Reply Address In.Sig} wrote:

>The Natural Philosopher wrote:
>
>> I ask, because having switched from line A with ISP A, gaily synching at
>> 6dB margin and achieving >4000 synch rates, despite having noise margin
>> reset LINE B with ISP B, is now on 12dB margin synching reliably at
>> just over 3000Kbps..This is at the same premises.
>>
>> The ISP claiming that BT cant, or wont, hardwire my noise margin.
>>
>> I am wondering if indeed they simply cant supply adequate bandwidth to
>> the exchange..and this is policy, not technical..
>>
>> Because the switchback always occurs at precisely 9:30 a.m. Whereas I
>> would have thought a noise margin reset would have been more or less
>> when an arbitrary counter gets to a value..
>
>I always thought the noise margin is a measured value at the receiving end
>and is determined by the line quality. Your line B sounds as though it might
>be locked to 3000Kbps because it could go faster with a reduced noise
>margin. You're not asking the correct question.

The margin is what the value is at the time you look. It may be that it
goes down to 6dB at night and that gives the upper limit of 3000Kbps
but in the daytime the noise decreases. This makes it look as though
the line could do better whereas the speed is set by the worst case
noise so that it's stable.

Mine has varied between 7.5 and 10.5 over the last 24 hours but I have
a constant sync of 8128.

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk

In article <(E-Mail Removed) ohitsystems
..ltd.uk>, Rodney Pont <(E-Mail Removed)> writes

>Mine has varied between 7.5 and 10.5 over the last 24 hours but I have
>a constant sync of 8128.

Can I check whether I have this right? A higher margin is desirable
because it ensures data quality at the expense of sync speed, yes/no?

It doesn't matter whether I set the margin to 1dB or 10dB, I always get
a sync of 8032kbps. So I just set the margin slider at 100%, which gets
me a pretty constant reported margin of 10-11dB.

Netgear DG834GT with DGTeam firmware.

--
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(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
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In article <qgjJm.130730$(E-Mail Removed)2>, Ato_Zee
<(E-Mail Removed)> writes

> chaining
>a couple of filters in series on the phone side,

What does that do?

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(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(") http://imgs.xkcd.com/comics/windows_7.png

Ato_Zee wrote:
>>>> I am wondering if indeed they simply cant supply adequate bandwidth to
>>>> the exchange..and this is policy, not technical..
>
> With a compatible router and DMT Tool you can set a lower
> SNR margin, and the line does indeed go faster.
> Unfortunately if you do it during the day or when
> noise is low, and the noise increases, your
> lower DMT Tool set SNR, will be reset back by BT.

This is esentially what is happening.

> The DSLAM looks at the reported figures from
> the customers modem and adjusts the SNR to
> reduce the error rate.
> Some routers perform better than others and give
> better speeds, and above all it pays to put your
> router next to the master socket.
> My sync speed was 2528kbps, has been as
> high as 5920kbps, and is at the moment 5408kbps.
> Most of the improvemet came from moving the
> router to alongside the master socket, chaining
> a couple of filters in series on the phone side,
> and finding a better modem.

done all that.

> Ask here for opinions on the best modem/router,
> if you want to start a long thread, followed by a
> flame war tagged on the end of the thread.

don't want to change. The router is perfectly capable of synching much
higher: Bt keeps increasing target noise margin so it wont. Why?


> It's not a BT conspiracy.
> Your sync speed is the size of the pipe, whether
> your ISP can fill it, well that is another story.

Why is it so hard to understand the point that:

My router synchs and holds happily at 4K or more and reported SNR of
7-11dB (presumably 9dB margin target). then BT decides it will run to a
12dB target. At 9:30 a.m. precisely, the router resynchs at 12dB or more
SNR, and the speed drops concomitantly.


I've already GOT the gain turned fully up. Packet loss and errors are
not that high. total noise is no worse than before.

i.e. is BT using a mechanism that is supposed to negotiate down to a
reliable speed for *your ADSL line*, to negotiate down to a reliable
speed their backhaul can cover?

By artificially increasing the target noise margin when there is no real
need to do so?

I had two lines here: I have moved ISP and a new router to a different
line. The performance noise wise is no worse that the old one was, the
only difference is that BT are setting a far higher target noise in this
one than they did on the last one and strangling its performance

Mike Tomlinson wrote:
> In article <qgjJm.130730$(E-Mail Removed)2>, Ato_Zee
> <(E-Mail Removed)> writes
>
>> chaining
>> a couple of filters in series on the phone side,
>
> What does that do?
>
reduces RF into the phone side of things a bit more.

But its still hissy.

The Natural Philosopher wrote:
> Mike Tomlinson wrote:
>> In article <qgjJm.130730$(E-Mail Removed)2>, Ato_Zee
>> <(E-Mail Removed)> writes
>>
>>> chaining
>>> a couple of filters in series on the phone side,
>>
>> What does that do?
>>
> reduces RF into the phone side of things a bit more.
>
> But its still hissy.

If you're hearing hiss, with or without filters in line with the phone,
it's because there is something causing intermodulation on the line.
That is - a non-linearity is causing a mixing of the frequencies in the
DSL signal, and is generating ADDITIONAL components down in the audible
range. The most likely cause is a high resistance connection. Oxidation
on the contact surfaces forms a diode, which will act as a pretty good
mixer.

The Natural Philosopher wrote:

> My router synchs and holds happily at 4K or more and reported SNR of
> 7-11dB (presumably 9dB margin target). then BT decides it will run to a
> 12dB target. At 9:30 a.m. precisely, the router resynchs at 12dB or more
> SNR, and the speed drops concomitantly.

No idea why 9:30am should be the time the DSLAM decides it knows best,
but my experience is that a high target SNR takes about 3 weeks of VERY
stable line conditions before it will drop to a lower value. In my case,
I tweaked the modem coding to give an artifically low sync speed (you
can do this with a Draytek). I let it run for 3 weeks (NO resyncs !),
and reset the coding. DSLAM then resync'd at a target SNR of 6dB.

(It doesn't take much in the way of repeated noise bursts to push the
Target SNR back up again - such as happens in the summer during
lightning storms).

Yes is the answer.

"The Natural Philosopher" <(E-Mail Removed)> wrote in message
news:hd3j4h$8vt$(E-Mail Removed)...
>I ask, because having switched from line A with ISP A, gaily synching at
>6dB margin and achieving >4000 synch rates, despite having noise margin
>reset LINE B with ISP B, is now on 12dB margin synching reliably at just
>over 3000Kbps..This is at the same premises.
>
>
> The ISP claiming that BT cant, or wont, hardwire my noise margin.
>
> I am wondering if indeed they simply cant supply adequate bandwidth to the
> exchange..and this is policy, not technical..
>
> Because the switchback always occurs at precisely 9:30 a.m. Whereas I
> would have thought a noise margin reset would have been more or less when
> an arbitrary counter gets to a value..

On Sun, 8 Nov 2009 13:05:35 +0000, Mike Tomlinson wrote:

>In article <(E-Mail Removed) ohitsystems
>..ltd.uk>, Rodney Pont <(E-Mail Removed)> writes
>
>>Mine has varied between 7.5 and 10.5 over the last 24 hours but I have
>>a constant sync of 8128.
>
>Can I check whether I have this right? A higher margin is desirable
>because it ensures data quality at the expense of sync speed, yes/no?

A higher margin is desirable but only up to a limit. You don't really
want to push the margin up above 6dB if it pushes your sync speed down.
You also want the margin high enough so that it doesn't go to 0 at the
worst time of the day.

My 8128 sync speed is the maximum for ADSL so a higher margin won't
help me. When the exchange is upgraded and I'm on ADSL2+ it should help
me but I know I won't get the full 24meg.

>It doesn't matter whether I set the margin to 1dB or 10dB, I always get
>a sync of 8032kbps. So I just set the margin slider at 100%, which gets
>me a pretty constant reported margin of 10-11dB.
>
>Netgear DG834GT with DGTeam firmware.

I've never seen 8032 as a sync speed. Is that the maximum the DGTeam
firmware runs at on ADSL?

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk