Inconsistent SNR

I live in rural Northumberland at the end of a long wire from the exchange. When things are going well my sync speed is in the range 1728 - 1792 kbps which gives me a profile of 1500 kbps. This is achieved with a noise attenuation of 58/59 Db and SNR of 15 for large parts of the day (although it drops single figures sometimes in the dark hours).

When things are going not so well, the sync comes in at 1532 to 1696 kbps which knocks my profile back to 1250 kbps. I then have to wait until I get another good connection and claw my way back to the 1500 profile.

I have routerstats set to reboot the router if the sync speed is 1696 or lower for 20 minutes and it will keep on re-booting every 20 minutes until I get to the 1728 sync threshhold.

My problem is that the SNR varies wildly after re-boot. I am currently connected at 1764 and the SNR has been pretty much solid at 14/15 Db for the last 27 hours - some spikes down to single figures but nothing below 6. This is an exceptionally good connection on my line and I daren't disconnect or I will lose it. Other times when I re-boot, at whatever sync speed I achieve the SNR is way down in the single figures and drops down to negative in the dark hours until the router drops out - so I have to keep re-booting till I get a good connection.

As nothing changes at my end or in the infrastructure as far as the exchange, what causes such changes in the SNR - a drop of 250kbps in the profile is not a lot for you city boys, but it cuts my download speed by 16%?

Gone Postal

Dell Inspiron 1501, XP SP3, Netgear DG834G (v3), Post Office Broadband.

what causes such changes in the SNR

If the Signal stays the same it has to be more Noise - AM radio propagation is stronger after sunset so there's more of that around, more folks at home with more appliances switched on too.

What router/chipset are you using?

I switched to a Broadcom chipset and it certainly helped my dropping SNR on a 51db line.

See the link in my signature below for more details...

Hi

have routerstats set to reboot the router if the sync speed is 1696 or lower for 20 minutes and it will keep on re-booting every 20 minutes until I get to the 1728 sync threshhold.

That explains the High target SNR . Rebbooting too often results in the dslam treating your line as unstable .
quote noise attenuation of 58/59 Db and SNR of 15 for large parts of the day (although it drops single figures sometimes in the dark hours).

You should be able to synch at about 2752Kbps with the default SNR of 6db . The high target SNR has cost you about 1000Kbps .

The SNR margin drop is showing that there is an increase in noise during that time .
These spikes are BAD news could be REIN causing loss of synch.
Regards Jeff

Are your line stats any better when the router is connected into the TEST socket within the BT master socket, assuming you have that type as shown in the link below:-
http://www.dslzoneuk.net/socket.php?type=html

Disconnecting the ring wire can make an improvement regarding noise pick up problems, but as mentioned already it's not a good idea to have the router rebooting that often as it just screws things up with the exchange equipment. Too many resyncs can make that equipment think the line is unstable and hence the target SNR in your line's case is cranked up to the known maximum.

My own line is too unstable for MAX so it was decided that the 2 Meg connection was the way to go, sync speed is fixed at 2272 kbps down and 288 kbps up.

In reply to a post by Anonymous:

That explains the High target SNR . Rebbooting too often results in the dslam treating your line as unstable .
quote noise attenuation of 58/59 Db and SNR of 15 for large parts of the day (although it drops single figures sometimes in the dark hours).

You should be able to synch at about 2752Kbps with the default SNR of 6db . The high target SNR has cost you about 1000Kbps .

The SNR margin drop is showing that there is an increase in noise during that time .
These spikes are BAD news could be REIN causing loss of synch.
Regards Jeff

Your opening paragraph may be right, may be wrong. The trigger figure was set originally at 10 times per hour and no-one has reported that being altered to 3 per hour.

That's by-the-by though.

I think you are incorrect to say "You should be able to synch at about 2752Kbps with the default SNR of 6db"

First, the poster said the noise margin drops from 15dB to single figures at night. That is a drop of at least 6dB therefore connection would be lost if the margin started at 6dB. Also many routers will lose connection as soon as the margin falls below 3dB, never mind reach zero. Though some will hold to -1 or even -2dB.

Second, on ADSL Max a change of target margin by 3dB alters the connection speed by between 500 and 750 kbps. So assuming the line could be stabilised by the noise source being removed he stands to gain 1500-2250kbps.

I don't think spikes were mentioned. Just wide variation.

Chaps/chappesses

Thanks for the comment - in answer to one of the questions, the bottom line of my original posting shows Netgear DG834G v3. In answer to other questions, I can't get at the master socket without a house dismantling job as the socket is behind a built-in bookcase - I can get at it but only by taking all the books and shelves out and pulling the back panel forward. I know that's not sensible, but it's the way it is. Finally, I know that continual rebooting will not allow the line to settle down at a sensible sync speed. As I said in my first posting I currently have a connection at a sync speed of 1760 kbps and SNR which is solid at 15Db for most of the 24 hours. My profile has now gone back to 1500 kbps. OBviously I am not re-booting while I have this connection.

All of the comments have been good stuff but none of them really address my question. The problem is that I can connect at a SNR of 15 and a sync speed of 1760kbps. I can then reboot and within the time it takes to re-boot connect at a SNR of 6 and a sync speed of less than 1600kbps. I was trying to get at the possible reasons for that variation in line quality.

Gone Postal

I was trying to get at the possible reasons for that variation in line quality.

may not be the line, need the test socket info to know and if that's not available it's a bit of a dead end,.

Phil

Thanks anyway. Next time she is spring-cleaning I might try and have a go.

Gone Postal

Try another router if you can get hold of one and see what happens with the line stats especially the SNR values.