Line stats

I was just wondering if anyone knew anything about line stats really...

I've always connected to the exchange at 8Mb, and the downstream attenuation used to be 14 db, with a noise margin (downstream) of between 14 and 16 (about 2 years ago).

I checked again for the first time in ages last night, and the attenuation had risen ever so slightly to 15 db, and the noise margin was around 13 / 14.

We had a powercut earlier today, and I thought I'd have another look at the stats. The atten. is now 14 again and the noise margin is about 12 / 13. Did the powercut cause the slight change, or was it coincidental?

Is it normal for noise margin to drop slightly over time? Will it stay at 12 / 13, or will it continue to drop over the years? And what is an acceptable noise margin for a line which synchs at 8Mb and has an attenuation in the mid-teens?

Thanks.

Edited by deleted (Tue 13-Oct-09 14:43:09)

These differences are not ever so slight. The scale is logarithmic not linear, so 3dB represents double for example.

As long as the SNR Margin is above 6dB at all times, then it is acceptable.

I wouldn't worry much about the odd dB here and there, if you have over 10 dB of margin there's plenty to keep it stable. I had an 11 dB line with a margin around 9 (from memory) so your's looks fine.

Thanks.

I guessed there's nothing wrong, but I was just curious about the figures as I don't really know much about them.

Why did both the atten and noise margin drop by 1 db after the brief powercut today? Did they really drop slightly, or is it just the router measuring them differently after it got reset due to the powercut?

the noise margin probably dropped because there was a bit more noise around when it resynced after the power cut.

Attenuation may have dropped because a different profile of frequencies were in use, less of the higher frequencies which have higher attenuation perhaps. If the thing shows you bits/tone across the frequency range it may become clear.

Thanks for explaining that.

Is there any explanation for why the noise margin is (on average) a couple of db lower than it was 2 years ago? I was just wondering if it'll continue to drop each year at the same rate!

Could be any one or a combination of reasons, I think your worrying too much, you never know in a couple of years you might have fibre to your local bt cabinet and a 50mb line

I am hoping - still on 2mb althought exchange is up to 24mb, nmind I chose to live miles away from it!

Here's a shot of the graph I got using RouterStats in the last few hours. It pretty much looks the same whatever the time of day is.

http://img106.imageshack.us/img106/96/captureij.jpg

The spikes between 12db and 14db obviously isn't a big deal, and I think it's something that's always happened. I've read that SNR margin normally drops at night, but mine doesn't. So I suppose it's better that it fluctuates during the day rather than dropping wildly at night lol.

I wonder if my router (Netgear DG834v3) is just not very good at reporting the stats accurately, after all its a router and not an instrument for measuring noise primarily lol.

P.S. I've always had my router connected to the mains via a rather long mains extension cable, I wonder if that might pick up some noise.