Noise Margin - High good or bad?

Started by joe, Jun 30, 2010, 11:23:06

Previous topic - Next topic

0 Members and 2 Guests are viewing this topic.

joe

I am confused.  I previously thought that a low figure was desirable but at the w/e my Noise Margin (RouterStatsLite - 2Wire 2700HGV) dropped to 1.2dB from a regular 9.0dB over the precedding fortnight. The d'ld speed achieved was pathetic - it predicted 25hrs to d'ld a file of 699Mb (Ubuntu). Yesterday morning Noise Margin was up to 11.8/12dB the highest its been and the connection speed has dramatically improved back to 13000 from the lowly 9000 it has been recently. D'ld of Ubuntu now took just 10mins.

I then read some glossary which appeared to suggest that a high Noise Margin was desirable showing a big difference between siganl strength and noise but Rik's replies seem to suggest that a low figure is desirable.  Whish is right?

kinmel


The higher the SNR, the more stable the line and from that the fewer errors.  Every error packet has to be resent and so the very best line performance comes with the highest profile that has few errors.

The BT line management system automatically increases the SNR when large numbers of errors occur.

The best SNR on a good line is 6dB, it should only drop below that at night
Alan  ‹(•¿•)›

What is the date of the referendum for England to become an independent country ?

Bill

Quote from: kinmel on Jun 30, 2010, 11:28:43
The BT line management system automatically increases the SNR when large numbers of errors occur.

That's the trouble with it. Even if interleave is on and they're FEC errors (ie don't really matter) it still jacks the SNR up :mad:
Bill
BQMs-  IPv4  IPv6

Steve

Steve
------------
This post reflects my own views, opinions and experience, not those of IDNet.

Bill

Quote from: Steve on Jun 30, 2010, 11:51:23
Its basically just lazy then.

Well. whoever wrote the code was... and "lazy" isn't the adjective that immediately springs to mind :P
Bill
BQMs-  IPv4  IPv6

Bill

Quote from: joe on Jun 30, 2010, 11:23:06
I then read some glossary which appeared to suggest that a high Noise Margin was desirable showing a big difference between siganl strength and noise but Rik's replies seem to suggest that a low figure is desirable.  Whish is right?

They both are, depending on circumstances.

If your SNR is stable then a low one is preferable to get the extra speed.

If it's not then a higher one might be preferable for increased stability (ie less resyncs). I've seen mine vary by 8db at times, so a target of 9db means I don't get resyncs halfway through the download of a big file!
Bill
BQMs-  IPv4  IPv6