Line Sync problems - gradual decrease over last month

I wonder if anyone here can shed any light on this issue as I can see it never being sorted out.

My line was converted over to adsl2+ sometime in February, this gave me a sync of around 4800 - 5300 or so. It used to fluctate a bit between those figures on a resync - generally it would be stable at the 5.2k mark giving me a 4.5 ip profile. I was very happy with this.

At some point around 6 weeks ago it started to go downhill until last week I was syncing at just over 2000. I thought the 1st step down was odd as I was no longer seeing any variance in the sync at a reset - it was syncing in the low 4000's and I just hoped it would go back up over time - at the 2000k sync I finally phoned tech support.

After a bit of to and fro something was reset at the exchange leaving me with .... the same 2k sync but over 19 snr. A bit more phoning resulted in some disconnects sunday morning and the problem seemed to be fixed - I had a high 4k+ sync other stats looked normal. Since then im back down to 3068.

A few things ive noticed -
When its went down a "step" theres no variance in the speed at a resync - when it was at the 3k mark every resync would be at 3068, when it was at 2k it would also resync at the same speed every time. Currently i can resync my router and every time I will get the above speed. Even if i knock my snr target down to 10% or increase it i will see no variance in the sync speed whatsoever. When it was "normal" I was used to seeing quite a bit of variance with in a given range on a resync.

As my down sync has dwindled my up sync has increased - again when things were normall this would be 460 - 600 or so - currently at 800 and prior to the exchange resets at the weekend at over 900.

Currently my line is back on the retraining stage - what i can forsee happening is being told my MSR after all of this and BT refusing to investigate further. I should add ive done all the usual - disconnected all phones, swapped filters, swapped routers and even tried a different cable that runs between the filter and router.

Anyone have any ideas?

It may be useful if you post your current router stats (up/down attenuation, margins, syncs). See http://www.dslzoneuk.net/adsl_line_stats.php or http://kitz.co.uk/adsl/frogstats.php

Have you tried forcing your modem to standard ADSL?

ADSL Link Downstream Upstream
Connection Speed 3068 kbps 792 kbps
Line Attenuation 54.0 db 28.4 db
Noise Margin 6.7 db 9.4 db

Heres the stats from my dg834v4.
I know im on a bit of a long line however ill stress that for 3 - 4 months I was happily syncing along at an average of 5200 - with the odd 4600 - 5600 sync.

The above stats would look fine I suppose, rebooting at the moment will alawys result in that 3068k sync.

Ive not tried forcing it to standard dsl, im not sure what the outcome of that would be, I might give it a go now.

-edit -

Interesting - I just forced it to g.dmt (normally its ADSL2+ (G.992.5) )and it the stats are as follows -
ADSL Link Downstream Upstream
Connection Speed 3072 kbps 704 kbps
Line Attenuation 52.0 db 29.0 db
Noise Margin 17.9 db 10.0 db

Edited by Beegs (Tue 14-Sep-10 15:18:02)

Since you changed Modulation the figures make more sense.

It looks like your Target SNR has been increased. If you stay stable it should reduce. Undocumented: 3db every 14 days of running stable.

Looks like your line/kit may not like ADSL2+ ?

FWIW: I'm on 51db Attenuation and sync'd at 5824 with a 6db Target SNR on 20CN/ADSL.

Ditto, I think the OP's line may perform better on standard ADSL rather than ADSL2+. I'd be tempted to leave it on standard ADSL for a week or so.

Ive left it for a few days to try and settle down.
I take your points about adsl 1 however it was good for months as adsl2+ - i did see an increases in my connections speed when it was increased.

What I find puzzling is how it connects at a fixed number every time, tweaking the snr up or down dosent change this nor does resyncing. Prior to this odd line behaviour snr tweaking would have a noticeable effect on my sync speed and a resync would definately see some variance with the speed it connected back at.

I guess all i can do is wait it out for another week or so and see what happens then, though im not hopeful.

I suppose your ISP has the capability of capping your line at a specific speed, but 3068kb/s seems an odd choice.

Were you tweaking your SNR margin lower for extra speed before? That might have triggered the resyncs and indirectly have caused a cap.

In reply to a post by Beegs:

Ive left it for a few days to try and settle down.
I take your points about adsl 1 however it was good for months as adsl2+ - i did see an increases in my connections speed when it was increased.

What I find puzzling is how it connects at a fixed number every time, tweaking the snr up or down dosent change this nor does resyncing. Prior to this odd line behaviour snr tweaking would have a noticeable effect on my sync speed and a resync would definately see some variance with the speed it connected back at.

I guess all i can do is wait it out for another week or so and see what happens then, though im not hopeful.

I found exactly the same thing happened to me when I moved over to ADSL2+ 6 months ago. I was trying to force my SNR lower and this may have added to the problem but it would always sync at the same low speed. My ISP decided that my line didn't like it at all and I was moved back to MAX but stayed on the WBC/21CN network.

I get similar speeds to yourself even though my line stats look better


Channel: FAST, Upstream rate = 768 Kbps, Downstream rate = 4384 Kbps
Link Power State: L0
Mode: G.DMT
Channel: Fast
Trellis: ON
Line Status: No Defect

Training Status: Showtime
Down Up
SNR (dB): 8.9 11.0
Attn(dB): 42.0 28.5
Pwr(dBm): 19.8 12.5
Max(Kbps): 4416 888
Rate (Kbps): 4384 768

Incidentally, I spoke to my isp today to find out what the longest period my line has stayed up without a resync and it was 11 days. This may be why have a target SNR of 15db 6 months on. My line drops several times a day and after 3 years of putting up with it I am leaning towards getting an engineer out.

Is your ISP reselling BT's ADSL2+? LLU operators don't seem to suffer from these problems.

Yep im on ADSL 2+ 21CN and my isp is ADSL24.

The only LLU operator currently on my exchange is TalkTalk, which from what ive read may just be a whole different can of worms... We are supposed to be getting C&W at some point in the near future, though i have read varying reports on them also. Id be tempted to switch to their LLU when it becomes available in the event that this isnt sorted out by then.

re: the question on the snr - yes i had the snr tweaked to 70% but that was left as it was for long enough and gave me the few months of 5k+ syncs. Granted my line wouldnt have been making14days+ uptime, id say it was dropping every 4 days or so on its own. This didnt seem to have any effect on the overall scheme of things until out of the blue after 3months+ it started to plummet, and only since then have i seen these odd "fixed" syncs.

Edited by Beegs (Fri 17-Sep-10 13:48:11)