SNR Problems

[Realist]

Not so long ago this was a fairly rare event. However, since the recent bulk speed upgrades, many users have found themselves on a faster connection, but they get frequent loss of sync to the exchange.
This FAQ should be read in conjunction with my page on Line Stats which explains attenuation and SNR.
~ Why does this happen?
The most common problem on longer lines is that your SNR is too low to maintain a steady connection. For each upgrade between the speeds you can expect to lose on average 6dB. Therefore if you upgraded from 512kbps to 2Mbps then your SNR is likely to have dropped in the region of 12dB.
Once your SNR starts to drop below 10dB then you are likely to have problems.

~ So what is happening?
SNR can vary on an hour to hour basis, not is it affected by the speed of your connection but there are other things may reduce your SNR. Hot weather can cause a long line to expand. Wet weather on a connection somewhere could cause dampness and deteriorate the signal. Even street lighting and flashing xmas tree lights have been known to affect SNR.
Your router or modem can either hear the signal from the exchange or it cant. If it cant "hear".. or to put it correctly cant sync with the exchange, then your adsl connection is lost and you are said to have "lost sync".

~ What are the symptoms?
Obviously the first thing you will likely notice is that you wont be able to surf etc. If you look at your router/modem the green adsl light will be flashing rapidly, rather than a steady green light you get when your modem syncs to the exchange.
Some routers provide logs that tell you when you have lost sync - my router would show as follows:-
Date/time : MAJOR ALARM : ATM Interface Down : Interface - atm-0
Date/time : MAJOR ALARM : DSL Interface Down
Other symptoms are lots of HEC and CRC errors in your router log.
Disconnects can be very random, you may get several all at once, you may get them just in the evenings, you may go through a bout of d/cs and then go days/weeks before you get anymore.
It all depends upon the severity of your problem.

~ Are there any tests I can do?
You can check your line stats from your router/modem to find out your SNR Margin.
Details how to get your line stats for common routers/modems.
Interpreting your line stats.
Its also very worth while checking and comparing your SNR to an SNR taken from the test socket behind the master telephone socket.
Simply remove the 2 screws from the faceplate and you will see a test socket on the lower RH side.
If you get a better SNR reading from the test socket then you should definitely think about purchasing a NTE5 adsl faceplate.
When checking from the test socket it is important that you only remove the faceplate and do not tamper with any of BT's wiring.

BT test socket.
photo adapted from Clarity - Main Entrance - Clarity UK

~ Can I do anything about low SNR?
Depending upon the severity there are different things you can try:-
- Routers are known to provide a more stable connection than usb modems and the purchase of an adsl router has done the trick for some.
The Netgear DG834 and Westell 6100 are 2 routers that have been known to maintain a more stable connection on a low SNR line. The D-Link DSL-G604T has also been reported* to successfully stabilise a low SNR line which was about to be declared as incapable of supporting adsl.
- Fit good quality adsl filters.. or even better....
- Fit a NTE5 master socket adsl faceplate, which is proved to have the best success rate.

~ What is an NTE5 adsl faceplate?
The NTE5 faceplate for the master socket is something that you can purchase and fit yourself.
It splits your voice and adsl data at the point of entry to your property and provides the most effective form of filtering available.
Fitting an adsl faceplate negates the need for separate filters in your home.
* Note although it is legal to fit a new NTE5 faceplate, you are not allowed to fit a complete NTE5 box, or tamper with the wiring on the BT side of things.

~ How do I install a NTE5 master socket faceplate?
Clarity do an excellent guide here.

~ Where can I purchase a NTE5 faceplate?
www.clarity.it
www.solwise.co.uk

~ How can I re-wire user side internal telephone cabling with Category5e/6 cable?
Re-wiring your internal telephone cabling with Cat 5-e cable may help reduce interferance caused between the point of your master socket and extension. You may find this useful only if you get a good stable reading from the master socket but need to connect from an extension socket.
There is a good guide on how to do this by readman here.
How ever there is something else you could try which has proved beneficial for others.........
~ One last trick - remove the ringwire.
A few guys on adslguide have recently had success by disconnecting the ring wire, which can improve your SNR Margin. This trick is particularly useful if you have an older style star (or spur) wired telephone system and you cant fit a NTE5 faceplate.

The "orange" ring wire can act as an antennae and introducing additional noise on the line. Adsl filters have their own capacitor, therefore taking the ringwire out of the loop still means that your phones will ring.

Phil (better known as Yarwell on adslguide), has already written an excellent article about removing the ring wire, therefore I see no point in replicating his hard work and instead refer you to his page here.


ADDED: This tutorial was originally posted at:
::. Kitz - Low SNR Margin & problems .::