What is SNR?

First question I have is what is SNR? also
My line was recently swapped due to a fault, my SNR is 15 is this normal?

Signal to Noise ratio. I believe its how much "louder" your signal is to the background noise on your line.

I THINK its the higher the number, the better

Edited by wrtpeeps (Sun 01-Oct-06 16:42:03)

SNR is 'signal to noise ratio' and is different to the 'noise margin' quoted by ADSL modems and routers.
The 15db you're seeing is a 'noise margin', and may be viewed as being the difference between the ADSL signal, and the background noise on the line.
In very rough terms, the background noise could increase by 15db before your router will lose the ADSL signal and get swamped by noise.

15db is a very high noise margin figure to have (the default is 6db for BT wholesale provided lines), and only occurs when the BT monitoring systems have decided your line is unstable at the old noise margin.
This can occur as a result of a line fault (in my case, a dodgy router and a series of thunderstorms). When the BT systems 'bump' up the noise margin, usually is steps of 3db, until they see a stable line.

Now you have your fault repaired, you're stuck with a 15db noise margin, which will be giving you a much lower sync (connection) speed.
You now face a battle with your ISP and BT wholesale (who you can't talk to - even though it may help), to get your margin reduced, or your line re-trained.
Best of luck! I've been at this stage for about three months, and have got nowhere (other than frustrated, and now holding the belief that BT is truly one of the most incompetent companies out there).

Edit: To clarify 'SNR'. It is a ratio between signal level and noise level (both being expressed in db). As it's a ratio, it has no unit.

Edited by adebov (Sun 01-Oct-06 16:59:13)

apologies, it appears i gave you the totally wrong info, thats adebov for the information

Or it could be that he's not on MAX.

But with limited info, and 15db margin being the common result of a dodgy line, it seemed the most logical suggestion.

I am getting the 15db reading from the DMT tool could I not reduce the Target Noise Margin in DMT or should I ask BT to retrain the line?

Sorry I didn

Info from home Hub


Uptime: 0 days, 0:12:12
Modulation: G.992.1 Annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 7,072
Data Transferred (Sent/Received) [KB/KB]: 131.00 / 407.00
Output Power (Up/Down) [dBm]: 12.0 / 19.5
Line Attenuation (Up/Down) [dB]: 10.5 / 23.0
SN Margin (Up/Down) [dB]: 24.0 / 15.5
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 0 / 0
FEC Errors (Up/Down): 0 / 91
CRC Errors (Up/Down): 0 / 0
HEC Errors (Up/Down): 0 / 0

What are the FEC Errors?

As you're so close to the maximum 8128kbps, you may be able to get there by tweaking the target margin using DMT (assuming the home hub will accept it).
Most margin tweaks only allow a maximum shift of around 5db, but lowering to 10db target should give you enough of a speed boost to get to the magical 8128kbps (you may not get all the way, as it appears you've got "interleaving" turned on).
Interleaving assists the router with error correction, when a line is a bit flaky or noisy. This is where the FEC errors come into it. They are corrected errors and nothing much to worry about.

Whether to get your ISP to turn off interleaving, or not, is down to how you use the internet. As you'll probably only get an extra couple of hundred kbps by having it turned off, unless you do a lot of online gaming (where ping times are important), you may as well leave alone.
As I said, it aids error correction in your router, and although it results in a slightly lower sync (meaning, if you sort out your margin, you won't be able to sync at 8128kbps with interleaving), giving you a 7Mbps maximum speed profile instead of 7.15Mbps. Hardly anything worth worrying about, and you'll still get a maximum speed of around 6700kbps (of course, it's highly unlikely you'll get that speed at all times, or maybe never).

If you do manage to tweak your router, you may have to keep an eye on it. AFAIK only the Speedtouch routers can save the tweaked settings, other tweakable routers return to pre-tweaked settings following a reboot or power cycle.
Trust me, it's easier to tweak the router yourself, than to get BT to reduce the margin at their end (because that will NEVER happen).