I know there are more recent threads on crosstalk, but as this one poses a general question and I have posted on it before (and replying to myself so as not to annoy anyone else!) I thought I'd add a little more information after looking at some old logs.

I had been syncing at 72152 for over two months (higher, incidentally, than I had managed since the very first few days after installation two years previously). On 26 June, some time between 1458 and 1808, my SNRM dropped from 5.9 to 2.8. The sync held at 72152 until 4 July, when the modem resynced at 60373, and it has remained there or thereabouts, with a SNRM of about 6, ever since.

So, something happened on 26 June. Could this really just have been a neighbour getting FTTC? Seems a bit drastic. Whatever it was, I am looking forward to vectoring, which hopefully will get me back up to full speed.

In reality I am not at all concerned about getting speeds of around 60 Mbps rather than 70 Mbps as it makes no practical difference, but I am concerned that it took such a large hit all in one go and that it could happen again.

well see my recent thread, if my recent issue is further crosstalk I have gone down from 110 to 53mbit. Still on fast path so not reduced by DLM. Although I currently have FEC on fast path it appears to have not had any significant affect on sync speed and I Was down to 55 without FEC anyway.

Find someone else with a DS sync of 55 who has full US speed with nearly 10db margin (and that is with power cutback applied on the US also). My DS seems massively hindered.

Edited by Chrysalis (Mon 01-Sep-14 17:18:24)

In reply to a post by kasg:

I know there are more recent threads on crosstalk, but as this one poses a general question and I have posted on it before (and replying to myself so as not to annoy anyone else!) I thought I'd add a little more information after looking at some old logs.

I had been syncing at 72152 for over two months (higher, incidentally, than I had managed since the very first few days after installation two years previously). On 26 June, some time between 1458 and 1808, my SNRM dropped from 5.9 to 2.8. The sync held at 72152 until 4 July, when the modem resynced at 60373, and it has remained there or thereabouts, with a SNRM of about 6, ever since.

So, something happened on 26 June. Could this really just have been a neighbour getting FTTC? Seems a bit drastic. Whatever it was, I am looking forward to vectoring, which hopefully will get me back up to full speed.

In reality I am not at all concerned about getting speeds of around 60 Mbps rather than 70 Mbps as it makes no practical difference, but I am concerned that it took such a large hit all in one go and that it could happen again.

That's what pretty much happened to mine, started off at 52 then went down to 40 in pretty much 1 hit and then again from 40 down to the current 32 again all in one go, both of them are thought to be because of crosstalk so if it's like mine then yes it could easily happen again on your line.

In reply to a post by kasg:

So, something happened on 26 June. Could this really just have been a neighbour getting FTTC? Seems a bit drastic. Whatever it was, I am looking forward to vectoring, which hopefully will get me back up to full speed.

I saw similar instances on my connection.

SNRM would drop suddenly by 2 dB or so & remain there for a few days.

The connection then resynced with SNRM back to 6 dB, but with lower sync speeds.

This happened around 5 times over a 12 month or so period.
Previously able to sync at around 30 Mbs, occasionally 34 Mbps upward, it now syncs at around 19 Mbps when Interleaving is ON & at around 21 Mbps when it is on fastpath.



A couple of visiting engineers & my own stats records have been unable to determine the cause & the assumption is that it is indeed due to increased crosstalk as more users become connected.





We had a fairly brief power cut in the area last night & as the HG612 modem does sync quite quickly when powering up again, it appears my connection resynced slightly earlier than some other connections when power was restored.

I ended up with a sync speed of 24975 Kbs & attainable rate of 30944 Kbps.

However, by the time this resync was captured by my monitoring program (a minute or so later), other connections must have become live again as my DS SNRM was (& still is) around only 0.9 dB.

I fully expect my connection to resync within the next few days, back down to between 19 & 21 Mbps.


I understand that a single new connection can have a drastic effect crosstalk-wise.
It apparently depends exactly where that pair sits within the cable bundle as to how severe the effect is.



So yes, maybe a single new connection could have quite a devastating effect on sync speeds/attainable rates.

In reply to a post by Bald_Eagle1:

However, by the time this resync was captured by my monitoring program (a minute or so later), other connections must have become live again as my DS SNRM was (& still is) around only 0.9 dB.

0.9, wow, I thought 2.8 was precarious enough!

In reply to a post by Bald_Eagle1:

I understand that a single new connection can have a drastic effect crosstalk-wise.
It apparently depends exactly where that pair sits within the cable bundle as to how severe the effect is.

So yes, maybe a single new connection could have quite a devastating effect on sync speeds/attainable rates.

Then it looks like I got off very lightly for over 2 years. My "clean" range on the BT wholesale checker is 60 to 79.5 so I am right at the bottom end now.

my (Current) clean range is 69.5 to 80, I say current because I suspect BT will change it if I become enough of a nuisance, when I had engineers out earlier in the year they reduced my estimate trying to be clever.

I am 17 mbit below the bottom of my clean range and 5 mbit below the bottom of my impacted range. Plus in the last 2 hours my dsl now keeps dropping, so things seem to be getting even worse.

In reply to a post by kasg:

I know there are more recent threads on crosstalk, but as this one poses a general question and I have posted on it before (and replying to myself so as not to annoy anyone else!) I thought I'd add a little more information after looking at some old logs.

I had been syncing at 72152 for over two months (higher, incidentally, than I had managed since the very first few days after installation two years previously). On 26 June, some time between 1458 and 1808, my SNRM dropped from 5.9 to 2.8. The sync held at 72152 until 4 July, when the modem resynced at 60373, and it has remained there or thereabouts, with a SNRM of about 6, ever since.

So, something happened on 26 June. Could this really just have been a neighbour getting FTTC? Seems a bit drastic. Whatever it was, I am looking forward to vectoring, which hopefully will get me back up to full speed.

In reality I am not at all concerned about getting speeds of around 60 Mbps rather than 70 Mbps as it makes no practical difference, but I am concerned that it took such a large hit all in one go and that it could happen again.

I lost over 11dB of SNR on the Downstream a few months ago within the space of an hour so it's quite possible.

My max attainable has went down from 124 mbps to 108

but my sync is still max 80/20

In reply to a post by kasg:

0.9, wow, I thought 2.8 was precarious enough!

Have a look at my SNRM graph in MyDSLWebStats.

It'sbeen pretty damned steady at around 0.9 dB for the last 26 hours or so.

I wish I could tweak it down permanently as per for ADSL connections.

In reply to a post by Chrysalis:

my (Current) clean range is 69.5 to 80, I say current because I suspect BT will change it if I become enough of a nuisance, when I had engineers out earlier in the year they reduced my estimate trying to be clever.

They did this to me too, but I'm now below that estimate too, lost around 10Mbps from my already flakey unreliable line because of what I assume is crosstalk