SN/R line variation

CurlyWhirly · 26 Apr 2006 at 11:57

After monitoring my line stats for a number of weeks, I can see a pattern emerging which is that in the morning and afternoon my SN/R rises to 29.5 dB but in the evening falls down to 24.5 dB

This happens on a daily basis but is it normal and also the variation is around 5 dB which seems quite high!
I wonder if this could be because in the evenings (when some people get home from work) and log on that this 'activity' can cause general SN/R margins to drop?

Also does this mean that when I am on Max DSL, I am likely to see speed variations throughout the day depending on what my SN/R margin is at that particular moment in time?

Finally with Max DSL, how often does RAMBO analyse your line stats to determine your speed so as to avoid you getting disconnected if your SN/R margin falls too low say to below 6 dB?

Skilldibop · 26 Apr 2006 at 12:11

SNR can increase and decrease daily for many reasons, but it's quite common if your line passes a device that is routinely activated and deactivated.
The bad news being there's around about nothing you can do about it.

Other users SHOULDN'T cause SNR deteriation as the voltages are very low. shouln't go more than 5V ish. This would only happen if there is dodgy cable that isn't properly twisted pair. This is highly unlikely as BT are pretty good at wiring things up.

tolien · 26 Apr 2006 at 12:23

Skilldibop said:
Other users SHOULDN'T cause SNR deteriation as the voltages are very low.

Back in the real world, crosstalk's a very real issue.

Finally with Max DSL, how often does RAMBO analyse your line stats to determine your speed so as to avoid you getting disconnected if your SN/R margin falls too low say to below 6 dB?

As often as you get disconnected.

It means if your SNR margin drops far enough, you'll lose sync (and probably resync at a lower speed). The SNR margin should then go back up, but you shouldn't get kicked off.

Skilldibop · 26 Apr 2006 at 12:34

tolien said:
Back in the real world, crosstalk's a very real issue.

It happens but not badly enough to make a 5dB drop in SNR, unless it's near end crosstalk, which it won't be unless your line is crap which wouldn't change much on a daliy basis.

Causes are academic anywy as there's naff all you can do about it other than ask BT to move you to a new exchange. Which they won't, and there's no gurantee that the interference is happening beyond your green box.

CurlyWhirly · 26 Apr 2006 at 16:54

tolien said:
It means if your SNR margin drops far enough, you'll lose sync (and probably resync at a lower speed). The SNR margin should then go back up, but you shouldn't get kicked off.

Thanks that explains what will happen to me when I'm on Max DSL

Incidentally after a bit of research I found out that crosstalk can make a slight difference to SN/R levels and also that your line speed is determined dynamically every time it syncs to the exchange so Max DSL is a 'dynamic' system!