What things affect ADSL noise margins?

Question

Recently my ADSL line has started having problems. While it has some problems during the day, it become almost unusable at night. with due to frequent disconnects/loss of sync. I looked at the line attenuation and noise margins to try and find the source of the problem. The line attenuation are are good at 11-18 on the down stream and 6-7 db on the upstream. However, the noise margin is awful. The upstream SNR (signal to noise ratio... aka noise margin) is fairly steady at 6-7 db. However, the downstream varies widely and very frequently. My modem updates the stats every 5 seconds and the numbers will vary greatly with every update. It may be at 3.7 db at one point and 18 db 5 seconds later.... then 30 seconds later it is at 30.2 db, before it drops back down. What can cause such wild variations? The noise margin will still vary during the day, but the fluctuations are often much more drastic (and often much lower) at night. So could you tell me what things, both inside and outside the house, can affect the SNR so much? I know things outside the house usually fall under the phone company's domain... but I would still like to know, so the phone company can't just try and pin everything on 'inside the house' issues. I have filters on all devices connected to the phone lines... but any other recommendations are welcome.

Thank you, in advance.

Answer 1

There are many specific reasons why this may be occurring, however all of them come back to a physical problem of some sort on the line. Whether this is at your home or somewhere closers to the central office, is another matter entirely.



If you have changed anything in your home which connects to the phone line (new cordless phone, fax, alarm system, answering machinte...). I would try unplugging the new device and see if your connection improves, if not, then try taking the dsl modem and a laptop out to where the phone line comes into your house and unplugging the service disconnect in the phone box on your house. then plug the dsl modem in it's place (you'll need a phone cord with the dsl modem to do this, as well as power and an ethernet cord). Plug the whole assembly together, if the problem persists, it is on the phone company's side, if the problem goes away it's inside your house.



If it is on the phone company's side, call them and explain that you are having trouble with your dsl service and explain the troubleshooting you've already done. Then request that they test the line (they may even offer before you request). They can usually do this remotely without having to dispatch anyone out to the site. If the test determines that there is a trouble on the line, they will dispatch to resolve the issue.

Answer 2

Adsl Noise Margin

Answer 3

There are three common causes of this problem. But only two are likely given that the problem is recent:



1) The lines are flooding underground. If this is the problem, your noise margin will be worse about 4-8 hours after it starts raining. When it's dry for several days, your noise margins will be good.



2) You have changed something in your house wiring. Perhaps you added an alarm system, moved a cordless phone, or added a satellite TV receiver. This change was made either without using a DSL filter or using a broken or sub-standard DSL filter.

Answer 4

The noise margin you HAVE depends on the distance between the internet connection and your local exchange and the quality of the cabling used

(if you put the internet connection in some far corner of your house and there a loads of extra cabling or extension sockets between it and where it enters your house then this will make it a lot worse)



The noise margin you NEED depends on the connection speed. The higher the speed then the better the noise margin you need for it to work reliably



If you lower the connection speed as supplied by your ISP then you will need a lower noise margin (its possible that halving your connection speed will give you a 100% reliable connection)



(I had the problem the other way around - I had a very good connection, but my ISP without notifying me doubled my connection speed (a freebee) and my connnection suddenly became unusable

It was only when my phone supplier came to check the line that we found out that the ISP had doubled the connection speed. . Returning the speed to as before the problem disappeared)

Answer 5

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