Target Noise Margin

Although at the end of a long line (60 dB attenuation) I have always had a stable connection and synched at 6dB noise margin.
Last Thursday the RCD tripped on the mains box. This I confirmed to have been caused by my wife's steam iron but not before it tripped out 3 or 4 times more. I should, of course, have disconnected the router but did not! I believe that as a result my target has been raised to 9dB with the consequent reduction in sync speed. It is not a huge issue as I am not a speed junkie but would like it reset if possible. The connection has been uninterrupted since. Will BT's system automatically reset after a suitable period? If not is there anything I can do?

If you maintain sync without dropping for an unrealistically long period of time, the BT systems should eventually notice and drop your SNR back down to 6dB

Tbh, I've never seen it happen without some gentle nudging.

You have a couple of options:

1. Request an SNR reduction by raising a fault at http://faults.plus.net Skip past most of the questions as they're not necessarily relevant (although you'll have to "answer" them all). Finally, make sure you explain in detail (like above, which was spot on) why you want your SNR reduced.

If you get no joy, try to grab the attention of one of the Comms team who should be able to action this on your behalf.

2. Use the DMT tool to force your SNR down to 6dB. This is dependant on having a router that is supported by the DMT tool. In my experience, using the DMT tool 'encourages' the BT equipment to notice that a lower SNR is stable so it *might* (with a bit of luck and a thousand pygmies) drop you back down to 6dB on it's own.

Edited by Caligulae (Mon 13-Oct-08 12:29:32)

10-14 days of stable sync with no very high error rates should cause the DSLAM to reset the target to 6dB and cause an automatic re-sync.

Mine happened during the 10th day, even though I accidentally switched the router off on the 8th night.

Apparently BT have become even more resistant to helping with SNRM issues, so until you have tried the wait you would be lucky to get anywhere . Unless you happen to get hold of someone who is pally with a BT person who can sort it in a few seconds.

A couple of weeks ago my error counts went through the roof, I lost sync and on re-connect DLM had raised my margin to 9db. Remarkably, a manual re-sync the very next day had me back down at 6db. To say I was surprised is an understatement! I was definitely only at 9db for that single-day because I had been monitoring my SNR prior to the wall of errors

That sounds to me more like the reconnection happened while noise (SNR) was still up by 3dB, (which means SNR was low by 3dB), and SNRM was set to your normal 6dB. So you had a lowish sync, (500-750kbps low), but the noise burst had gone by the time you checked the SNRM so SNR and SNRM had both gone up by 3dB.

In other words just the same as sync'ing at night then looking at the SNRM in the morning.

Manual resync just returned things to normal.

Any idea what not high errors are?

Ive been in sync for 17 days with no more than 700 CRC's per day and no reduction in SNR. (was 6 with 49dB Att with approx 6000 sync, now 5400 sync so loss of 1meg due to bras!)

Cheers

Sorry, BT don't give out any clues as to the error rates allowed, and strangely nothing has leaked out over the years.

700 CDCs per day actually seems high to me. (Upstream or downstream?) Have you any idea what it used to be? Also what caused the rise in SNRM? If it was automatic then I would expect it to have dropped. If you reported some sort of fault before the rise then it is possible an engineer has raised it and turned off the auto feature. That is the nightmare scenario I'm afraid as that is the difficult thing to get altered.

Full stats would help. I would be tempted to try a re-sync anyway and see what results.

I've been tweaking the target SNR in my Netgear router to reduce it from 15dB to 9dB which gives me a stable connection at 7616 (interleaved) instead of around 5000-5500 at 15dB. But there is no sign of BT reducing my target SNR automatically. Tweaked SNR or not, I've held sync for 14+ days many times so I can only assume my error rate is above the unpublished threshold.

I am now using the connection less, especially in the evening, to see if a lower error count will prompt the BT system into action. If that fails I'll move to LLU, probably Virgin/C&W (no Be at my exchange).

In reply to:

---

1. Request an SNR reduction by raising a fault at http://faults.plus.net Skip past most of the questions as they're not necessarily relevant (although you'll have to "answer" them all). Finally, make sure you explain in detail (like above, which was spot on) why you want your SNR reduced.

---

I did just that at 09.30 yesterday morning. 24 hours later my target margin was back to 6dB. Full marks and thanks to Keith & Ben.

Excellent! Glad they could help.