SNR Margins

Could someone please explain to me, in a reasonably simple way, SNR margins. Some time ago I was having a problem with slow download speeds ( there's a surprise ) and Talk Talk Boy asked me to PM him my stats, which is what I did. He lowered my SNR download margin from about 25dB to about 6dB and this resulted in my download speed improving to about 4.500 Kbs which was great. Since then it has been almost consistantly the same figure until two weeks ago when it dropped to 1.800Kbs. I did a stats check and the SNR download margin was 22.5dB so I asked around and I got several conflicting pieces of information. I was told that the SNR margin should be as high as possible but this didn't seem to agree with what happened when TT Boy lowered it to about 6dB. I checked the SNR download margin one hour ago and it was 8.5dB giving me a download speed of 4.200Kbs. I am not very technically minded but I am not too thick either so can anyone help me on this one? I am on LLU exchange in the East Dorset region if that helps. Many thanks.

SNR is Signal to Noise Ratio. In its most basic sense it just means how much noise you have on the line in comparison to the actual broadband signal (the higher the SNR the louder your signal is in comparison to other noises/interference on your line). If the noise drowns out the broadband signal then the connection will drop and you have no broadband.

SNR is different from line to line and also changes depending on how fast the line connects at. Increasing the connection speed will drop the SNR, which can then make it more susceptible to disconnections/resyncs. Decreasing the connection speed will increase the SNR often making the line more stable.

When people say the higher your SNR the better they mean that having a high SNR is always better then having a low SNR at the same connection speed. Because it means that your line is usually going to be more stable at its current connection speed, and also that the line will be able to cope with even higher speeds if they become available.

In your case, previously when your router went to connect to the broadband service it was told not to connect at a speed which caused an SNR any lower then 25dB. TalkTalk Boy edited your connection profile to tell your router that it could now connect at any speed up to 6dB. Which inevitably allowed the router to connect at a much higher speed.

Edited by DonnieD (Fri 28-Mar-08 15:23:42)