ADSL Router - reported Noise query

[Scoob]

Hi,

I live a long way from the exchange, really, right near the limit by all accounts. However, I've always gotten what I considered reasonably good speeds, usually just over 4mbps, giving me around 400 or so kBps download speeds. I was happy with that, living right out int he sticks as I do.

My ADSL Router, and older Netgear DG834G v3, reports my Line Attenuation as ~51db and my Noise Margin of around 6 - 9db for this connection speed.

Some time ago I was having NIGHTMARE broadband issues, my Attenuation went as high as 60+db while my Noise Margin went up to 15+db. I'd get a 300kbps connection at best, that'd last 5 minutes if I was lucky.

Now the various faults have been address, numerous places were rewired outside the property and they fitted an RF filter and an updated ADSL 2.0 master socket (I had the original ADSL 1.0 socket before), my Attenuation is back to 51db and my Noise Margin is usally between 4 and 6db.

Since this was done I get the best connection speeds I've ever had, usually at least 4500kbps and as high as 4800kbps, this gives me between 470 and 505kBps download speeds. Very nice.

However, I've been told that a LOWER Noise Margin value is BAD and it should be higher - totally contrary to what successive BT Engineers told me. Indeed, at one point during the faults being resolved, I was back at my normal 51db line Attenuation, but my Noise Margin was still in the teens and my connection was crap. Only when the numbers fell back to 6db and below on the Noise Margin and stay there did my speed improve.

So, can anyone explain things to me please? I'm guessing it's just my old router reporting things slightly differently to some of the modern, more advanced stuff.

Basically, for a given Line Attenuation - which is usually 51db for me - I always see better connection and speeds with a LOWER reported Noise Margin. As my line improved during the fault resolution process I saw my Noice Margin slowly drop, which fit in perfectly with what the BT engineers were telling me.

Just a bit of a puzzler for me, the conflicting information and all - I thought I knew a reasonable amount about this stuff, however when various "authorities" on the subject directly contradict each other, and my own results appear contrary to the accepted norm, well, I though I'd ask here

Cheers,

Scoob.

 

[insomnarium]

Noise Margin (AKA Signal to Noise Margin or Signal to Noise Ratio)
Relative strength of the DSL signal to Noise ratio. The higher the number the better for this measurement. In some instances interleaving can help raise the noise margin to an acceptable level.

6dB or below is bad and will experience no synch or intermittent synch problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with little or no synch problems* (but see note below)
20dB-28dB is excellent
29dB or above is outstanding

* Note that there may be short term bursts of noise that may drop the margin, but due to the sampling time of the management utility in your modem, will not show up in the figures.

Line Attenuation
Measure of how much the signal has degraded between the DSLAM and the modem. This is largely a function of the distance from the exchange. The lower the dB the better for this measurement.

20dB and below is outstanding
20dB-30dB is excellent
30dB-40dB is very good
40dB-50dB is good
50dB-60dB is poor and may experience connectivity issues
60dB or above is bad and will experience connectivity issues

I hope this helps

Cheers!

P.S. No matter how old your Netgear router is, problems with signal are usually caused by bad lines (copper pairs which oxidate by time, etc) from your house to your ISP.

 

[Scoob]

Hi insomnarium,

Thanks for your reply.

The information you've posted is what I've read elsewhere, yet does not tie in with what I'm experiencing now.

Just over the last few days my BB has been a little odd. My Line Attenuation went up to 54db from 51/52db - but nothing really changed. However when my Noise Margin went from 6db to 8-9db my connection went from 4,800 to 4,100kB/s.

Now my Noise Margin has dropped back to 6db, my connection is back up to 4,700kB/s - this behaviour is consistant, which simply doesn't make sense, as a WORSE Noise Margin should equal a worse connection BUT the lower that number for me the consistantly better my connection, actual speed and stability are. It's darn odd!

Scoob.