Strange SNR Issue

Dear All,

This is making me pull my heair out so I am hoping someone can set me straight!

We were on ADSL Max on BT 20CN but was forced to upgrade to 21CN. We then took advantage of the upgrade and went from an 8Mb service to 20Mb service - at this point the circuit become unstable and I outline some more details below.

Since moving on 21CN, we have received multiple disconnects due to 'lost-carrier' as seen in our session history. A further diagnostics report run on the line has also shown that the we are on the absolute bare minimum of SNR Margin - averaging between 2-4db which is expected to cause disconnects. The current stats are SNR Margin of 3db, SYNC speed of 21Mb and the Loop Attenuation is 6db. We are physically close to the Exchange and the Line Attenuation of 6db seems to support that - however, the modem tries to sync at 21Mb every time you reboot BUT cannot remain stable and disconnects 11-20 times per day.

There is some other strangeness to share as well. I hope this helps in some diagnostics.

1. I have seen (when we first moved over to 21CN and upgraded to 20Mb) that the modem would sync at 17Mb and the SNR would be at 6db. So the connection does have the ability to sync at a lower speed BUT stable SNR. Why does it always revert back to the more usntable 21Mb on reboot? A BT Speed Test Results also said the Line Profile was set to 17Mb. So not sure why this is being ignored.

2. Overnight, there was a pattern forming that the circuit would break just before 2 hours (1h 59 mins : 58 seconds) 4 times on the trott. Does this not strike as odd? If the line was noisy why would it regularly break at a time just before 2 hours? During the day it would break but last longer or shorter. No huge pattern. I have spoke to the provider about duplicate logins, DNS and IP issues and they have triple confirm this not an issue with the connection.

3. Two Draytek 2830 Modems have been tried. 2 New filters have been tried. All cables have been replaced. The BT Master socket has been tried at the Engineer socket. No positive affect seen.

4. The SNR does rise when on the phone making a voice call - it raises from 2db to around 6db. This is indicative of a High Open which I understand needs an engineer to resolve. However, I am still baffled why the line was unable to just sync and stay synced at 17Mb @ 6db. If it can manage that, why not stay at that instead of going to the faster and more unstable connection.

My provider is (VERY slowly) arranging a SFI BT visit but its like pulling teeth. The reason I am posting here is that I just need some comfort from the expert community that this looks like a line fault rather then something else myself and the supplier is missing.

Thanks in advance.
Brad

Edited by deleted (Mon 26-Mar-12 14:30:43)

It sounds like BT's DLM thinks a 3db Target SNRM is ok for your line - your ISP 'should' be able to change this with the 21CN 'stability options' that are available to them. Have you tried asking them to increase your Target Margin?

Who is your ISP - always worth saying, so others get an insight on how providers work

It does sound as if you have a line issue if your SNR raises when the phone is in use - I take it you've tested directly via the BT Test Socket to ensure your internal wiring or equipment isn't effecting things?

The good news is you've got a nice short line that many of us would give their right arm for!

Hi B4dger,

The supplier is Daisy Wholesale but the underlying provider is BT Wholesale.

I have tested by the BT Test Socket and there is no gain in SNR. Wherever the fault is, I think its behind the Master Siocket and before/at the Exchange.

I also feel the BT Engineer is needed so I will order one in. Apparently I will get a SFI and be charged if the issue is on my side. To be frank, I am in such urgent need for a stable and fast connection (business based) that am more than happy to pay them to just come and fix it.

Sadly the short line is worth nothing until they find and fix the source - the question is whether they really will be able too or not.

Brad

In reply to a post by Brad_Porter:

I have tested by the BT Test Socket and there is no gain in SNR. Wherever the fault is, I think its behind the Master Siocket and before/at the Exchange.

Hi, you've confused me a bit
If you are saying things are fine when using the BT Test socket then that indicates the issue is not BT's. i.e. It's either your equipment/extensions/faceplate. So in theory BT would bill you - often around £200.

I appreciate what you are saying about just getting it sorted though as ADSL is so important.

Hi B4dger,
Sorry - I was a bit unclear.

What I mean is that when I test with the BT Test Socket no improvement is seen at all. The SNR is still low and I see regular disconnects. In essence, the isolation test (of any type) seems to make no difference.
Ironically, I have just checked my SNR now and can see that the line disconnected 1.5 hours ago and upon reconnect it sync�d at 18Mb and 5db SNRM. I know that it has sync�d before at 17Mb and 6db but after a reboot it always reverts back to 20Mb at 2db. Can anyone explain why it does this?

One final question - how do you get BT's attention enough to get them to come round and fix it. It really is not a money thing - I am just desperate for a stable and fast line for my business and just want to say �please come round, investigate and fix. Ill pay�!

Thanks
Brad

Dear All,

And another strange thing I wish to report.

Why do the disconnects follow the below pattern of disconnecting just before 2 hours - have a look at the logs from tonight in terms of my session activity.

Start Time Stop Time Duration Download Upload Termination Reason
31/03/2012 17:55 31/03/2012 19:54 1hrs 59mins 21s 574KB 761.56KB Lost-Carrier
31/03/2012 15:54 31/03/2012 17:54 1hrs 59mins 28s 581.48KB 789.32KB Lost-Carrier
31/03/2012 13:54 31/03/2012 15:54 1hrs 59mins 25s 571.25KB 761.14KB Lost-Carrier
31/03/2012 11:54 31/03/2012 13:54 1hrs 59mins 20s 575.31KB 780.31KB Lost-Carrier
31/03/2012 09:55 31/03/2012 11:54 1hrs 58mins 43s 663.94KB 940.66KB Lost-Carrier

If this was purely a SNR issue - why the regularity of breaks just before 2 hours?

Does this strike anyone else as odd?

Brad

Have you tried with some other than the two draytek 2830's

Not seen a 2 hr cycle down to 21CN kit, but maybe the drayteks in combo with the new exchange kit hit some bug in the software close to the two hour point.

Does a resync 30 minutes into the cycle reset in the resync in 90 minutes or another 2 hours?

You must be on dial-up!

Some dial-up used to discon every 2 hours.

It's the Draytek,

A friend had the exact same problem when he switched to 21cn, He complained to the isp resulting in an engineer visit which found no fault which he had to pay for.

I plugged in an old spare Thompson router and his connection was rock solid.
We then updated all the firmware in his Draytek to the latest versions, but it still cut out. Eventually he bought a cheap Netgear from Argos and hasn't had any problems since.

Hi,
You would need to ask your ISP to arrange for any BT work.

But take a look at the other responses here regarding your router and the 2 hour disconnects