Odd 21CN SNR / resync issue

Hello all,

At the end of January my local exchange got the 21CN upgrade and my line was changed to ADSL2+ shortly after. Prior to this I had sustained a full 8mbps ADSLMax connection with the following stats:
Down Sync=8128Kb/s LoopLoss=12.5dB SNR=14dB
Up Sync=832Kb/s LoopLoss=4.5dB SNR=16dB

For the first 8 days everything seemed great on ADSL2+, the stats were as follows:
Down Sync=20088Kb/s LoopLoss=17.1dB SNR=5.1dB
Up Sync=1240Kb/s LoopLoss=2.3dB SNR=6dB

There were a couple of resyncs, but the line was training so it was expected, however on the 9th day things became really unstable. Between 1am and 9pm the line resynced 47 times. Since then the line has had a couple of days where everything seemed fine and then periods of massive instability for no reason.

I've been using a DrayTek Vigor 120 plugged into a Linux server which does the PPP and NAT / etc, that modem has been rock solid since the day I got it. I've also tested with 2 separate Netgear DG834GT's both in modem (PPPoE bridge) and standard router mode. The line was refitted a few years back because the old line ran along the front of the house and the covering had been destroyed by the weather (we think it was the original line for the house). The new line is less than 50cm from where it emerged from the ground to my phone point.

There is no extension wiring, at all, and I'm using an ADSLNation filtered faceplate which I bought two years ago because the plug-in filter was sometimes causing net drops when the phone was used.

I'm really stumped as to what could be causing this. AAISP have been great and suggested trying a 9dB SNR but that hasn't helped. I've run routerstats and caught the line dropping on a graph, if that's any help:
http://i40.tinypic.com/6z57jn.jpg

Also, here's the line monitor graphs from A&A, I've left the stable days off, just showing the huge disconnects due to resyncs:
http://i41.tinypic.com/e66a9l.png

Has anyone seen anything like this? It's becoming infuriating and any help you could provide would be great.

In your modem can you force ADSL, ADSL2 and ADSL2+ modes ?

Try each of these for a day or so to see if that makes any difference.

Any of your neighbours got ADSL2+, if they have droppouts at the same times, then could be some local interference source that has just appeared

Woke up this morning to find my line had been set to a 20dB SNR and synced at 9mbps. Whilst this wasn't exactly good news, it did allow me to discover there were huge bursts of noise happening on the line.

A little while ago I stumbled across this page:
http://www.kitz.co.uk/adsl/rein.htm

Prior to the 21CN upgrade we had a digibox installed for the digital switch-over. I've unplugged this and the SNR graph went from "rocky" to much smoother. I'm going to leave things as they are overnight and see but if it was an interference issue from the box, hopefully things will settle down and I can get my DLM reset and get back to a 6dB SNR.

Is the digibox connected to the phone line? Or sharing same power strip as the modem?

Have you removed the ring wire from any extensions in the property?

In reply to a post by MrSaffron:

Is the digibox connected to the phone line? Or sharing same power strip as the modem?

Have you removed the ring wire from any extensions in the property?

Looks like the Digibox was a red herring. The line has lost sync 30 times since my last post. It was plugged into the same surge protector as the ADSL modem though.

There is no extension wiring at all and the mater socket only has 2 wires.

Time to unplug everything else or move the modem as a trial.

Why?

ADSL2+ uses extra frequencies so if the noise caused by something is only in the 1.1 to 2.2 MHz range that can explain why ADSL2+ shows the problem but ADSL was perfectly stable.

If you forced ADSL2 mode, you would avoid those frequencies, but be limited to a 12Mbps sync. As ever a trade off on stability versus speed.

In reply to a post by MrSaffron:

Time to unplug everything else or move the modem as a trial.

Why?

ADSL2+ uses extra frequencies so if the noise caused by something is only in the 1.1 to 2.2 MHz range that can explain why ADSL2+ shows the problem but ADSL was perfectly stable.

If you forced ADSL2 mode, you would avoid those frequencies, but be limited to a 12Mbps sync. As ever a trade off on stability versus speed.

I think my next step is to set the line to G.DMT (ADSL1) and see how things go with stability then. If it still has drop-outs then something else has changed because it was 100% stable prior to the switch. It's almost like I'm connected to a twitchy DSLAM or something.

Unfortunately the only neighbour I'm friends with is on TT LLU. He only lives 100m away but he hasn't had any problems since his switch.

Ok, forced the line into G.DMT. Sync speed is now 8192/1120 with a 10dB SNR.

Let's see how this goes.

Had an OpenReach "Boost Engineer" out today. He replaced the NTE5 with an Openreach branded one and replaced my ADSLNation XTE-2005 faceplate with an NTE2000 one. He also requested the banded profile be removed.

So far things have seemed stable, aside from a couple of initial re-syncs shortly after the work was done, but the line was up for 4 days (Thusday through to Sunday night) without issue. I guess we wait and see if things are fixed now.

He did say if the issue reoccurred it had to be either at the cab or the exchange as everything inside the property has now been changed.

Limiting the line to ADSL1 didn't help by the way. Still had the same type of random disconnections due to the SNR dropping. In the end the exchange stuck me on a banded profile with a 21dB SNR. When the drops occurred the SNR fell from 21dB to 0 in less than 5 seconds.

Just another update, hopefully the last.

Still had serious issues with the line after the engineer visit last Monday. A&A requested another visit. The engineer who came today, an SFI2 engineer I was told, was much more thorough and found an issue on the line.

It was eventually tracked back to the E side of the network and I've been changed onto a different line running from the cabinet into the exchange. All CRC errors on the line appear to have stopped and making / receiving calls no-longer drops the sync.

Hopefully this little journey is at it's end, we'll see how things pan out over the next week =)

I figured I'd post the outcome here, should anyone find themselves with a similar issue.