Slow Speed Saga

[#1]

Hi Community,
First post - but after lots of reads. I have a tale to tell of phone lines, routers, filters, monitoring programs, dragons and a call of distress... (well maybe not dragons).
Some history (short version). We are on a long line in the notorious black spot for broadband that is Milton Keynes. But we have had reasonably reliable around 1Mb/s service for many years. Until September 2009 when for a couple of days the telephone stopped working which BT fixed. Being not particularly observant we then noticed slower broadband over the next 3-4 weeks before reporting it to PlusNet. Various tests ensued (including BT saying your line is fine - but it will cost you if we have a look). Then PN sent us a ST516 router to try in place of our aging D-Link DSL604. It was definitely quite a bit better - though not quite right over next few weeks. And just before Christmas PN called and we agreed to buy the test router. We had good period from mid December to end of Jan with speeds occasionally up to 1.8Mb/s. Then every thing went wrong. Sync speed fell to 160k - throughput 112k. BT still say line is fine - cost you if we call around and find nothing.
New ticket raised with PN on 5th February (ID 31922759) and new series of tests follow - and I start reading these forums. So now equipped with RouterStat Lite and know how to get info out of the ST516. Noticed when made a phone call sometimes the signal got noisy. So ran with router plugged straight into test socket for around 4 days (no telepone) gradually getting profile back up and hopeful. But then overnight lots of noise and speed drops back down to 160k  :(. Ran on with just modem connected for several more days but no longer reliable. Needed telephone back as well so plugged that back in and reliability even lower. Bought an ADSLNation XTE-2005 faceplate - seemed like magic at first, sync back up 2200k and using phone made only minor blip in RouterStats trace. Even sent a hopeful comment to PN but it was not to be.... PN responded saying even if we think we are ok then  we are not! as their monitoring shows intermittent line and we are now "assigned to the correct pool" to deal with intermittency rather than speed. And they were right. Sync now keeps falling, using telephone again interferes with SNR levels, and even if we don't use the phone then the line goes through noisy times.
Where we are now. The ADSLNation Faceplate is still in place but performance is woeful. The stats from the modem are down below plus a screenshot of the last time we lost sync as seen by RouterStats Lite (note nothing we are aware of was happening at this time - no calls or abnormal activity). We are waiting for PN to respond on ticket after "further testing" and expect to finally insist BT send an engineer with the risk of a "fine" from them. I feel better for writing this all down and of course any new ideas are welcome. On the positive side should we ever get back to stability it looks like better than1Mb/s may be possible. On the negative in a few days time we must have sufficient bandwidth to support a video-conferncing session so I am going to try getting a 3G dongle going and hope that works.
Thanks for reading this tale.
Link Information
Uptime: 0 days, 3:34:58
DSL Type: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 160
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 13.0
Line Attenuation (Up/Down) [dB]: 30.0 / 56.0
SN Margin (Up/Down) [dB]: 15.0 / 30.0
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 3 / 0
Loss of Signal (Local/Remote): 11 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 3 / 0
FEC Errors (Up/Down): 2 / 684
CRC Errors (Up/Down): 2 / 46
HEC Errors (Up/Down): 2 / 31

Noise margin and connection speed plots from RouterStats Lite for latest loss of sync attached.

[#2]

That is the highest default noise margin I have ever seen on a normal ADSL line - you line must be really screwed to need it that high
What appears to have happened is that your line lost sync then reconnected at 15dB noise margin then after a lot of joggling up and down progressively increased as the line became less noisy
Unfortunately I have no experience of aluminium lines so I don't know if that is anywhere near usual but I doubt it

[#3]

It's not normal.
I suspect a sync of 160 is below the FTR (Fault Threshold Rate) and can be raised with BT.
Rest assured, if you have tried the standard troubleshooting steps (new router, filters, and plugging into the test socket) then Plusnet will fight any charges that BT may try to levy.
It seems like you have done everything at your end to isolate the problem.  To me, the fault certainly seems like a bad line so it really is the point in time to get an engineer booked.
I would suggest that you have all the records handy for the engineer, (they often turn up with nothing!) and plenty of tea and biscuits to help lubricate the wheels of fate
Cheers
B.

[#4]

Thank you oldjim and Barry.
Sounds like it finally is engineer time - I will check with PN on how best  to get them in. Thank you for the advice on getting evidence ready for them.
Hmm must check whether "highest default noise margin ever seen on a normal ADSL line" is worth an entry in Guiness Book of Records :).
Patrick.

[#5]

I thought I changed that  default has been crossed out 

[#6]

who is you phone service with? PN or BT, if BT report it to them as a noisy line but dont mention Broadband

[#7]

Phone is BT - the time we tried to report direct the noisy line on the telephone they just said no it isn't. We are more determined this time.
@oldjim my quoting you must have crossed with you fixing it!
Patrick.

[#8]

Hi
I've had similar woe recently, PN suggested turning on interleaving to reduce errors on the line and that got the speed from 320kbps to 800kbps. Latest router firmware then got it back to 2mbps where it had been before. Still can't get any where near 8mbps though.
cheers
john

[#9]

Thanks John,
Interleaving was switched on earlier in the process but has not made a noticeable difference. Switching routers to the ST516 (which does have the latest firmware) seemed to help for a bit and indeed that the line has periods when it works fine after trying something is one of the mysteries. Glad you are back up to 2Mb/s - our own connection today is worse than every with some complete drop-outs before struggling up to 160k. Along the way I feel that there were several useful things that I have picked up here or from PN suggestions such as changing router, installing the ADSLNation plate and monitoring with RouterStats Lite. My feeling now is that I am fighting some external noise source but I *hope* in the end to be on a better speed than the 1Mb/s I started with. At the moment though anything would be good!
Patrick.
P.S. Just tried to post this and have had 15 minutes of no connection at all - as attached.