SNR target margin query

Hi folks,

Ever since I've been with Xilo (about 2 years or so now) my rx sync has been between 10.5 and 11.5 (depending on the usual things.. time of day etc.). This seemed reasonable considering my stats:


Uptime: 0 days, 5:42:50
Modulation: G.992.5 Annex A
Bandwidth (Up/Down) [kbps/kbps]: 1,020 / 13,351
Data Transferred (Sent/Received) [MB/MB]: 24.68 / 193.90
Output Power (Up/Down) [dBm]: 12.5 / 0.0
Line Attenuation (Up/Down) [dB]: 17.5 / 37.0
SN Margin (Up/Down) [dB]: 8.0 / 3.0
Vendor ID (Local/Remote): TMMB / µ
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): 2,365 / 0
FEC Errors (Up/Down): 0 / 8,476,902
CRC Errors (Up/Down): 0 / 52,446
HEC Errors (Up/Down): 0 / 44,070

But my SN margin (down) has always been around 6dB. When there was a power cut this afternoon and the router re-sync'd, I see the SN margin is now 3dB!
Not like I'm complaining about getting a faster connection. Think BB speedtest is fastest I've ever seen.

Almost looks like my target SNR margin target has been reduced from 6dB to 3 dB (hence the higher sysnc).
Seems a little strange to me. I thought Xilo / Uno gave you a stock 6dB. Or am I misunderstanding what's happened?

Though the fec count does look a little high for only some 5+ hours connection time!

Any opinions on what appears to have happened?

Do you know if you are on a BT Wholesale connection, or is it LLU?

Some while back BT Wholesale altered their system so it will lower the target noise margin from 6dB to 3dB on stable lines. So if you are on one of theirs that could account for it.

Thanks for that.

I'm on partial LLU through xilo/uno (using TalkTalk kit I believe at the local exchange).

Edited by MrBeeline (Wed 10-Jun-15 23:09:04)

In which case it is very odd! But no doubt welcome .

O'well... it did not last. Not surprised with the number of errors it was logging.

Just re-sysnced and rx is around the usual 10.5 showing 6dB SN.

Think the old speedtouch router is maybe getting temperamental, as it doesn't hold the line as well as it used to. While the connection does appear to drop, all the correct lights on the router show fine (IE both DSL and internet connection lights are green). Router feels pretty hot at this point. Can't complain I suppose, as it's been running 24/7 for several years now..

Time to try one of the many other modem/routers that I've got in the cupboard. Just a hassle as there are so many devices these days that will need fettling to use a new router. God how did we manage without smart phones/tablet/laptops/sky/youview/kindle etc. etc. and it also means trying to remember how I set up that power line range extender. EEK....

As RobertoS has said, on a stable line it will "experiment" with a 3dB margin. However if that does not stand up and the error count is high it will revert to 6dB and may never try 3dB again, or at least for a while.

My old ADSL line sync'ed at 3dB and would not drop out or resync unless I forced it - my SNR could occasionally drop to 0dB or even negative occcasionally.