what SNR/SNR Margin at 0.5Mbps for reliable operation at 1 Mbps

OK, Now we've got the topic of what we mean by SNR and SNR margin well
staked out in its coffin...

Now to the question I really wanted to ask :-)

I have a 512kbps system working reliably at a downstream attenuation of
say 55 to 65 db.

What SNR/SNR Margin do I need to be seeing at 512kps to make it
worthwhile trying to upgrade to 1Mbps...? (see notes)

Bob

(Instruction to candidates
1) Credit will be given for clear, (or indeed any), reasoning
2) You should assume that the reliability required is that for normal
small business use (95/95 confidence limit??)
3) Do not write on both sides of the paper at once.)

--
robert w hall

robert w hall wrote:
> OK, Now we've got the topic of what we mean by SNR and SNR margin
> well staked out in its coffin...
>
> Now to the question I really wanted to ask :-)
>
> I have a 512kbps system working reliably at a downstream
> attenuation of say 55 to 65 db.
>
> What SNR/SNR Margin do I need to be seeing at 512kps to make it
> worthwhile trying to upgrade to 1Mbps...? (see notes)
>
> Bob
>
> (Instruction to candidates
> 1) Credit will be given for clear, (or indeed any), reasoning
> 2) You should assume that the reliability required is that for
> normal small business use (95/95 confidence limit??)
> 3) Do not write on both sides of the paper at once.)

Well at 65db line loss you can't get it, simple as that...

In article <412f7261$0$5888$(E-Mail Removed)>,
Kráftéé <(E-Mail Removed)> writes
>robert w hall wrote:
>> OK, Now we've got the topic of what we mean by SNR and SNR margin
>> well staked out in its coffin...
>>
>> Now to the question I really wanted to ask :-)
>>
>> I have a 512kbps system working reliably at a downstream
>> attenuation of say 55 to 65 db.
>>
>> What SNR/SNR Margin do I need to be seeing at 512kps to make it
>> worthwhile trying to upgrade to 1Mbps...? (see notes)
snip
>>Well at 65db line loss you can't get it, simple as that...

why? (or do you just mean 'won't')

I'd suspect the real limit is in SNR (*).
Bob

*I can think of a couple of hand-waving arguments, suggesting you could
need 6db of margin at 512, ie an SNR of about 12db; if so some of the
512kbps 60db setups I've seen quoted may be stretching it to get to
1Mbps.
But I am NOT SQEP in this area :-)
>
>

--
robert w hall

"robert w hall" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> OK, Now we've got the topic of what we mean by SNR and SNR margin well
> staked out in its coffin...
>
> Now to the question I really wanted to ask :-)
>
> I have a 512kbps system working reliably at a downstream attenuation of
> say 55 to 65 db.
>
Only half meg is going "no limits" but for one meg the new limit will
be -60dB. -60.1dB or higher will not be provided. The new limit for two meg
is -43dB.
Your SNR figure needs to be as high as posible, anything under 12dB SNR
(approx) may have some problems. You should be able to improve SNR by
disconnecting old or poor extension wiring. Fitting of a SSFP or NTE2000 at
the BT master socket is the best way to raise the SNR figure. Look on the
Clarity.it website.

Phill.

P H wrote:
> Only half meg is going "no limits" but for one meg the new limit will
> be -60dB. -60.1dB or higher will not be provided. The new limit for
> two meg is -43dB.
>
> Phill.

Ahhh, another one with the 'Extended reach CD'

--
reply to news at nytoo dot co dot uk

On Sat, 28 Aug 2004 11:56:11 +0100, in article
<(E-Mail Removed)> robert w hall
<(E-Mail Removed)> wrote:

> why? (or do you just mean 'won't')

Won't because even from 6th September BT's attenuation limits are:

1Mbit 60dB

2Mbit 41dB

I think they allow a dB or 3 leeway, so 65dB for 1Mbit is still not
allowed unless there happens to be a small reduction in loss on the day it
is tested or the estimated loss is less than the real loss.

--

Brian Morrison

please observe reply-to address

Brian Morrison wrote:
> On Sat, 28 Aug 2004 11:56:11 +0100, in article
> <(E-Mail Removed)> robert w hall
> <(E-Mail Removed)> wrote:
>
>> why? (or do you just mean 'won't')
>
> Won't because even from 6th September BT's attenuation limits are:
>
> 1Mbit 60dB

Correct

> 2Mbit 41dB

Wrong. It's going to be 43dB

--
reply to news at nytoo dot co dot uk

In article <4130f8cc$0$5888$(E-Mail Removed)>, P H
<(E-Mail Removed)> writes
>
>Your SNR figure needs to be as high as posible, anything under 12dB SNR
>(approx) may have some problems.

Ah - this is the sort of answer I'm after (and 12db confirms my
suspicions/prejudices) -- but

where does your estimate come from (MK trials, calculation, Ouija
board...)

>
>
>

--
robert w hall

On Sun, 29 Aug 2004 11:49:00 +0100, in article <(E-Mail Removed)>
"Nick" <postmaster@127.0.0.1> wrote:

>> 2Mbit 41dB
>
> Wrong. It's going to be 43dB

I refer you to:

http://www.adslguide.org.uk/newsarchive.asp?item=1814

that states that the attenuation limit for 2Mbps will remain at 41dB for
the time being.

But I believe that BT allow a margin of uncertainty on this in cases where
an actual measurement is deemed necessary.

--

Brian Morrison

please observe reply-to address

robert w hall wrote:
> In article <4130f8cc$0$5888$(E-Mail Removed)>, P H
> <(E-Mail Removed)> writes
>
>>Your SNR figure needs to be as high as posible, anything under 12dB SNR
>>(approx) may have some problems.
>
>
> Ah - this is the sort of answer I'm after (and 12db confirms my
> suspicions/prejudices) -- but
>
> where does your estimate come from (MK trials, calculation, Ouija
> board...)
>
>
>>
>>
>


My sig/noise at 1/2Mb is quite happy at 5.5dB, line length of 6.5km,
with a downstream attn of 67dB. Its been 100% for best part of a year
using a good D-Link 504 router.

My old house was further with worse (expected) figures, but they still
gave me the service. Used to drop out in the winter nights though.

A few months ago both my figures were well outside what BT said was
technically possible. I'm pretty sure that 1Mb would be well pushing it
for me but its strange to see how the criteria changes over the months.