Poor upstream sync

[#1]

Hi
I've been getting a few resyncs in the last week, not unusual as I am on a long line. Downstream sync usually stays around 3Mbps. However, recently the upstream sync has been badly affected, on one occasion as low as 64Kbps after resyncing.  Can anyone suggets a likely cause bearing in mind that the downstream sync is unaffected? Noise, faulty filter, router on the way out? Quiet line test is noise free.

[#2]

When you find out tell me as I have the same intermittent problem 
Does the resync occur when the phone is left to ring

[#3]

No link to the phone ringing at all, Oldjim.  The resyncs sometimes happen in the middle of the night.

[#4]

In which case I can't be of any help  as mine always occurs when the phone rings so presumably the ring voltage is upsetting things
You could try a different filter

[#5]

Good suggestion, I'll try that when I get the chance.

[#6]

I can see from your recent history of upstream sync speeds that on one occasion it was at 64kbps. It looks like it was a one-off and it is back to your normal sync now.
How are things at your end?

[#7]

From my experience it is highly intermittent and the upstream sync can drop to anything between 360kbps to 64kbps but the thing to watch is the noise margin. If it drops to 6dB on a resync then there is a problem
The actual sequence is that due to a burst of interference or cross talk between the upstream and talk frequencies the upstream errors to increase to the point where it loses sync. If the resync happens after the interference has stopped or reduced you will get full upstream speed but perhaps with a low noise margin
I can always see the upstream errors jump while the phone is ringing but not sufficiently to cause a resync
Note that on ADSL1 the reported upstream noise margin never changes unless there is a resync but on ADSL2 uncapped it does and this is on 21CN in both cases

[#8]

Hi Chris
All back to normal now and hopefully it will stay like that for a while.  From past experience the problem will recur in a couple of weeks though.

[#9]

Let me know if/when it does and I'll run a few checks on your line to see if there's any noticeable difference, also keep an eye to make sure no other electrical devices internally are on during that time that aren't normally.