Billion UK Forum

The SNR margin on my ADSL2+ has been capped by BT @ 30db resulting in very low downstream sync rate (3072kbps). This happened within minutes of me trying a TP-LINK modem on the line. After 4 days it's still being capped by BT @ 30db. Before I tried the TP-LINK modem the SNR was a constant 6db, without tweaks.

Is it possible to set the Billion 7800 to reduce the SNR from 30db to 6db? I have seen a lot of tables with possible values but only for reducing from a max of 18db.

BT are refusing to do an SNR reset for another 4 days so I'm hoping the 7800 can override their settings.

You can try and adjust your settings on hidden SNR page http://192.168.1.254/snr.html, but if BT have cappped your profile, I think the BT cap with over ride the SNR tweak on the 7800N.

You can try and start with 50 and keep dropping it by 5 until you reach your desired SNR value. After you have tweaked the SNR, the first time, and if there is no SNR change showing on the ADSL status page, this means the BT profile has over rided the 7800N tweak, it is then best to leave the device connected for required days, (try not to drop the ADSL during this time) and ask BT adjust the profile after the 4 days.

I set the SNR to 65400 (lower by 15db) and it resync'ed with pretty much the same noise margin:

DSP Firmware Version A2pB025f.d22k
DMT Status No Defect
Operational Mode ADSL2+
Upstream 1147
Downstream 3072
SNR Margin(Upstream) 5.9
SNR Margin(Downstream) 25.5
Line Attenuation(Upstream) 17.9
Line Attenuation(Downstream) 29.0

Can't believe I have to wait another 4 days

OK so my SNR was reset back to 6db by BT and was stable, so I thought. After 48hrs it dropped and reconnected @ 9db.

The question is - if I set the SNR back to 6db using the tweak, and BT continue to see errors will they try and increase the SNR margin even more from their end?

sheepie wrote:OK so my SNR was reset back to 6db by BT and was stable, so I thought. After 48hrs it dropped and reconnected @ 9db.

The question is - if I set the SNR back to 6db using the tweak, and BT continue to see errors will they try and increase the SNR margin even more from their end?

They might do, as this is automatted system that automatically adjusts your line, if it gets really bad the SNR tweak on the 7800N will not work and be overidded by BT. (Normally the BT profile will only kick in if there have been lots of disconnections on the line)

SNR margin has dropped again to 12db. I had routerstats running at the time and it looks like the cause was 400 CRC errors in very short time (less than a minute), where all other 15min CRC counts are under 40. I really wish BT's kit would not drop SNR margin after one-off errors like this.

I also have a few gaps in the tones, is this normal?

Hi

Gaps are normal, and more appear over time as noise causes tones to be turned off. Tones will only come back after a re-sync to just start getting attacked again.

Your line appears to be Fastpath, this means there is no error correction so noise will always create lots of errors. You would probably find an Interleaved connection would be more stable. Fastpath might be wanted if you play games and want as little latency as possible.

ADSL is seldom error free, it was designed to allow a certain amount of errors in order to push the old telephone wires to the max.

Regards

Phil

thanks for the advice Phil - those tones are always turned off even right after resync. As long as it's normal

I requesed fastpath because I play a lot of online games, it's surprising how much differnece an extra 20ms makes! I'd rather take a hit on the sync speed than have interleaved. CRC errors are usually within acceptable values (100 an hour maybe) but I have had the odd occasion where I've have 1000's in a few minutes.

Hi

Yes tones always off are not uncommon due to interference, not much you can usually do about it.

Fastpath will see a greater number of errors and drops due to bursts of noise, which is why you normally need a higher SNR to help protect against that.

Regards

Phil

they seem to be dropping my connection every 24hrs and setting a worse SNR margin each time, currently at 15db, maybe it's the fastpath that is causing them to record a highish CRC count over 24 hours. I don't really know what a high CRC count would be but yesterday I had router stats running all day and the 15min CRC count was usually under 20.
Not much more I can do until the after 10 days have pasted since my last SNR reset