DLM

I recently turned interleaving off on my line to lower latency.

I had my router running at 4db SNR and it was running fine for 5 days and then I looked at my router one evening and the sync had plummeted to 3968kbps and my SNR was 12db.

I have left it and it has been connected for 124hours at 3968kbps with an SNR of 13.5db.

I thought DLM reduced the SNR accordingly? Surely it should have dropped by now?

You just need to reconnect.

You had a bad sync caused by a sudden burst of noise, and the noise was (to some extent) still present when the reconnection took place. The noise has now gone, and it is daytime not night-time, so the observed noise margin is high.

Nothing will change until you reconnect yourself. Assuming you are on a BT Wholesale service though even after you get full connection speed it will take a while for the IP Profile to catch up, and you won't get full download speed till then.

You are thinking of what happens when your sync-time noise margin is raised due to a period of considerable instability. Given 10-14 days stability the system will reduce it by 3dB and automatically re-sync you, but that doesn't seem to be what has happened in this case.

Post the stats straight after a reconnection . That will show if the sync-time margin is still OK.

I think what may have caused it is me 'tinkering'. When the sync dropped I tried my hardest to get it back upto the 5Mb profile by reducing my SNR on DGTEAM. Finally realising my SNR was rising after every re-sync I set the SNR to 100% and left it.

I'll give it a resync and see what happens.

If DLM has raised the snr profile it could take months to fully recover if at all. The DLM once it became alerted to possible instability might of recognised your tweaking as more instability. The only thing i would do is tweak to the lower limits needed for the ip profile you are on to try and minimise line errors and leave it alone and hope the DLM shows mercy and the target margin sooner rather than later. Mine was only solved in the end by going back to interleaving.

12db SNR still.

What a pain in the bum.

How do I get this reduced?

In reply to a post by RobertoS:

You just need to reconnect.

If the DLM has put him up to 12db, which it seems like - a reboot won't set it lower.

Once to DLM thinks it is OK to set lower, it will automatically drop the sync/session and it'll resync at 9db or 6db as needed but as you say, can take weeks/months.

A quicker way to make this happen is ask the ISP to reset the line (and training period) which come in to play within a few hours.

Matt

In reply to a post by uno:

Yes, but I was going from the implication in the opening post that he had pretty well left alone since finding the low speed, high margin .

Which is why I asked him to do a re-sync and immediate stats.

Yes, the now-available full retrain is the quickest way of sorting out a 12dB target, but I wasn't expecting it to be needed. That would have come on seeing the new stats.

In reply to a post by wolvesmad:

12db SNR still.

What a pain in the bum.

How do I get this reduced?

See the last sentence of uno's post. Letting the DLM sort it out will take 6-7 weeks.

Well Matt, thanks for the info!. Uno/xilo are my ISP so if you think this is the way forward then I will be in touch in the near future.

Hopefully if my exchange is unbundled by C&W soon no DLM will be one of the bonuses of the migration across.

How is DLM triggered. How many times does the line have to re-sync before it goes from 6db to 9db??

Thanks.

That makes it even easier

BT don't give away what exactly causes it, so I doubt anyone could tell you that.

It isn't just based on syncs though, errors on the line also play a big part in the DLM changes.

Edit - I have just read your other post, and that drop in margin could be the issue. However, getting it reset may only make the line much worse and i'd put money on the fact that it'll go up to 15db within 3-4 days.

Matt

Edited by uno (Fri 25-Jun-10 21:45:45)

I'll drop a ticket in today and see if you guys can drop the margin

If I could somehow set the sync at 5120kbps then there is no reason why the line would not stay up for days. Pretty sure it was running at 6.1Mb when everything went pear shaped.

As for the noise, I have been suffering with it for years. In the summer months I used to be able to hold onto a 5696kbps sync for weeks.

One day my line speed halved and I found myself on interleaved. The line was very unstable and I logged a ticket with my then ISP Entanet who were very helpful.

BT apparently found a problem and cured it, not sure how but the line did appear to be more stable but come night time I would lose 2-3Mb. I said I wasn't happy and Enta said they could send the BT SFI team out but if they did not find a fault they would charge - heavily. This put me off persuing it as the noise is only present at night.

So I have a potential sync of just over 7Mb during the day,which will run stable until around 6-7pm and then a 5.1Mb sync for the night time.

My line attenuation over the years has creaped up from 45db to now 50db.

Pretty shocking as I am not actually too far from the exchange but I guess 5Mb is better than 1Mb............