SNR goes down at night

towel401

downstream only really, upstream sits around 15-17 always. usually downstream hangs around the 20-22 mark but during the night it goes down as low as 15 or 12 even. doesn't cause any problems just wonder why it does that

yayamark

dam i thought this was something erotic.

whats snr?

towel401

signal to noise ratio

yes it could be those lesbian vampire orgies but the SNR goes down even when those are not going on

Sponge Bob

as your neighbours stop using their BB the noise picked up reduces and your SNR improves ( goes down)

http://en.wikipedia.org/wiki/Crosstalk

Sad Professor

Sponge Bob wrote:

as your neighbours stop using their BB the noise picked up reduces and your SNR improves ( goes down)

I thought the higher the SNR the better? So wouldn't the low SNR at night mean there was more noise on the line?

Sponge Bob

snr ( attenuation) better if low , could be 1 in a lab .
snr (margin) needs to be 10 -12 minimum but as long as the margin is 12 it need not really go any higher.

different modems have different names for these key stats .I assume the OP is reporting atten not margin and his line is short ...500m max is it OP ??

towel401

i`m on about the margin. attenuation sits around 10/9 for upstream and downstream and is fairly constant. i`m about 250m from the exchange

Sponge Bob

So the margin drops close to danger territory at night , hmmmmmmm .

would it be street lights, can you see if there is a correlation between lights on and margin degredation and post back ????

towel401

could be.. but there aren't any lights on the roads from my house to the exchange. there are 2 little villages using that exchange i think maybe those are stealing my SNR

JNive

it could be a dodgy line that suffers from dampness when the sun goes down, check that :-)

lucernarian

There's probably no way of the modem logging the actual SNR throughout the day, but the times when it happens are important. See if there is a detailed pattern.

Does it stay like that at 4 am? If it is, then it would rule out the crosstalk issue. But I would imagine that a DSL line, if most of them are always-on, would generate the same amount of crosstalk no matter what time of day.

It would be handy to have a rough idea of when the time of this SNR drop finishes.

bushy...

To_be_confirmed wrote:

There's probably no way of the modem logging the actual SNR throughout the day, but the times when it happens are important. .

Most stuff like that does snmp , so it will return what you want if you ask it . Google for : make of router + OID + SNR and see .
Then you can get http://www.openxtra.co.uk/freestuff/mrtg-xtra.php (for windows) or mrtg for unixy stuff to draw graphs for you

lucernarian

Nice idea which would be good to try out. If I could get DSL. It will be interesting to see someone carrying it out.

towel401

To_be_confirmed wrote:

There's probably no way of the modem logging the actual SNR throughout the day, but the times when it happens are important. See if there is a detailed pattern.

Does it stay like that at 4 am? If it is, then it would rule out the crosstalk issue. But I would imagine that a DSL line, if most of them are always-on, would generate the same amount of crosstalk no matter what time of day.

It would be handy to have a rough idea of when the time of this SNR drop finishes.

yyea, at 4am it was hanging around the 14 mark, back up to 24 now. does the netopia router do this logging thing? i could write a script to poll the web interface or telnet but right now i don't even know how to get into the telnet thing [alwys says i don't have permission]

bushy...

Do it with mrtg , it'd be much easier , you give it the ip of the router and what you want to graph and its away

delos

Strange, my margin seems to be cut in half at night (Smart, Dillon's X Cork) starting from last night and continuing tonight. Its OK during the day and early evening.

lucernarian

It's bad at 4 am... that's what I was suspecting. I also suspect that if you tried it at 8 am that SNR would be better.

But there is actually a problem with that line. SNR should be nowhere near 12 dB for a 250 metre long line. It should be near 40dB if anything.

The sheer shortness of your line is making sure the line quality doesn't manifest itself. But so long as it stays connected, it won't matter what the SNR is like.

What package are you using? Does it ever suffer from disconnects? Are there any flourescent lights near the phone wiring? Do the phone sockets look tidy and well wired?

Xennon

We have found that the SNR varies on two separate exchanges dramatically between day and night and remains rock solid on a third that we monitor. The third one being my exchange which is out in the countryside. The other two are in build up areas, and seem to be powered from the local street light supply. We have found that the SNR variations coincide with daylight hours. We have been recording this for the past 6 months and using data from the met office for daylight hours, we can say that this has something to do with street lighting.

Watty has suggested that it may be the odd ballast used in the sodium lights that may be causing the interference on the lines as the phone lines run in close proximity to the street lights.

We have contacted Eircom about this, and worked with one of their lads to try and locate the cause of the problem, but he eventually gave up as he had more pressing issues, but in fairness to him he spent a couple of days entertaining a bunch of nerds.

One thing we do know is that both exchanges are powered from street light supplies. From what Watty and Sponge_Bob have told me it is unlikely that the actually supply is the problem as the exchanges run on a serious UPS setup, complete with filtering. The other possibility is induced noise as Watty suggests. However Im still not convinced one way or the other at the moment and hope to dig a little deeper into this before we can definitely say what the cause is.

The monitoring is done as bushy describes on snmp and mrtg graphing. For those of you on Windis there are packages out there that will do this for you. Google is your friend. Most routers have snmp compatability.

This only becomes an issue if you are on the limits of the DSL SNR limits. Some people will experience loss of sync as the SNR margin drops, and the only way around it is to move to a lower bandwidth package, which requires a lower SNR margin.

So interestinger and interestinger

Dave_W