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Standard User Bald_Eagle1
(experienced) Sun 12-May-13 19:41:57
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Crosstalk or something else?


[link to this post]
 
Well, my connection is now in sync at only 20764/4859 Kbps.

It has reduced in 3 steps to that level since December 2012.

In December, sync speeds were 29430/5704 Kbps, where they had more or less been for the 7 months since my connection was finally repaired near the end of May 2012.

DS Attainable rates have gone from 34Mb to 21.5Mb




Here's a before & after set of snapshot graphs:-


http://i.imgbox.com/ackiwNN4.gif


The really obvious differences are Bitloading, QLN & SNR.
However, I can also see slight deterioration in the Hlog graph, along with slightly increased attenuation as reported via the pbParams data.

I also notice that TX Power has reduced slightly.

Right up to May 1st 2013, Interleaving depth had been around 400-500 DS & 1 US since it was applied a few days after DLM was reset back in May 2012.


When the connection resynced on the fly at 04:54 May 1st at speeds of 24802/5172 Kbps, DS Interleaving was switched off completely.
INP & delay were also set to zero at the same time.

This was quite surprising as my 1000m connection does usually seem to need Interleaving, INP & delay to be applied at reasonably low levels.

There had been quite a few resyncs since 1st May, until appearing to settle at such low sync speeds.

I presume such low speeds no longer require Interleaving, INP & delay setting.


I disconnected all internal extension telephony wiring, switched the mains power off in my house & actually ran the connection for a while via a car battery & a battery powered laptop.
This made absolutely no difference to the stats obtained when fully mains powered, so I assume nothing in my own house can be causing such deterioration in speeds & stability.



Now, my question is, can this really all be down to increased crosstalk or is it possible that either something else has gradually caused QLN to deteriorate or is some sort of a line 'fault' brewing?


I have no idea how many users between the cabinet & my house have broadband connections or even which flavour(s) of DSL they are using.
I also have no idea how to discover if there has been an increase in the number of broadband users, coinciding with the dates I noticed a deterioration.


Does anyone have any ideas/suggestions?

I don't believe requesting DLM to be reset would have any mileage (even in the unlikely event that such a request would be granted), particularly as Attainable rates are so low & there doesn't really appear to be much in the way of spare SNRM.
Standard User RobertoS
(sensei) Sun 12-May-13 20:57:28
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Re: Crosstalk or something else?


[re: Bald_Eagle1] [link to this post]
 
I assume I'm talking about how to suck eggs if I ask about the test socket, replacement of the socket >> modem cable, and replacement of the modem/PS for it?

My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 54.2/15.2Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
Standard User Bald_Eagle1
(experienced) Sun 12-May-13 21:27:51
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Re: Crosstalk or something else?


[re: RobertoS] [link to this post]
 
Yep.

Done all that.

I even turned off all the mains power to the house & ran the HG612 from a car battery for a while, using a battery powered laptop to grab the stats.

I have also used a spare unlocked HG612 & a HG622 on the connection to no avail.


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Standard User RobertoS
(sensei) Sun 12-May-13 22:00:23
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Re: Crosstalk or something else?


[re: Bald_Eagle1] [link to this post]
 
Yep, I read that smile. But it's very rare for people to swap out cables - often re-using them when changing the kit at each end.

I agree with you it looks more like a specific cause such as deterioration somewhere, rather than just increased cross-talk due to additional connections.

Smart meters?

Battery-powered weather stations/radio-sync'ed clocks?

My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 54.2/15.2Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
Administrator MrSaffron
(staff) Sun 12-May-13 22:56:40
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Re: Crosstalk or something else?


[re: RobertoS] [link to this post]
 
Hope for a power cut and run the hardware up via batteries and everyone elses is off. If speed returns its cross talk

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User Chrysalis
(legend) Mon 13-May-13 01:09:26
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Re: Crosstalk or something else?


[re: Bald_Eagle1] [link to this post]
 
a big problem is one data is fast path and the other is interleaving.

interleaving usually bumps up the attainable rate so that alone stops it been comparable properly and of course also reduces the actual sync rate.

you not got both fast path comparisons or both interleaving?

To me it does look most likely crosstalk tho.

BT Infinity 2 Since Dec 2012
Standard User Bald_Eagle1
(experienced) Mon 13-May-13 23:07:14
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Re: Crosstalk or something else?


[re: Chrysalis] [link to this post]
 
In reply to a post by Chrysalis:
a big problem is one data is fast path and the other is interleaving.

interleaving usually bumps up the attainable rate so that alone stops it been comparable properly and of course also reduces the actual sync rate.

I posted the comparison graphs with/without interleaving just to show the differences since December when my connection was quite stable with 'reasonable' speeds.



you not got both fast path comparisons or both interleaving?

I do have relevant stats from as far back as November 2011, but as my connection can't usually sustain Fastpath at its usual higher speed, I didn't think it relevant for comparison purposes.
It has previously achieved over 30Mb sync speed with interleaving at a depth of around 400 or so.

My theory is that it only recently went back to Fastpath due to DLM seeing far fewer errors at such low sync speeds.

I'm trying to confirm why sync speeds are currently so low, without much success so far.


Plusnet have confirmed their own tests do actually show a fault, but I don't yet know what those tests were.



To me it does look most likely crosstalk tho.

Are you basing that on the deteriorated QLN graph or some other factor(s)?

I live in a relatively sparsely populated area & many residents are quite elderly so possibly less likely to be broadband users.
Standard User WWWombat
(fountain of knowledge) Mon 13-May-13 23:09:37
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Re: Crosstalk or something else?


[re: Bald_Eagle1] [link to this post]
 
In reply to a post by Bald_Eagle1:
In December, sync speeds were 29430/5704 Kbps, where they had more or less been for the 7 months since my connection was finally repaired near the end of May 2012.

What was the original estimate for your line?

DS Attainable rates have gone from 34Mb to 21.5Mb

As Chrysalis points out, the attainable figures when interleaving/FEC is turned on turn out to be artificially high.

So the likely realistic drop is from around 31Mbps to 21Mbps - so you've lost about a third of the line's throughput.

I think this is still within the bounds of "expected behaviour", even if it isn't very nice to experience.

My line, over the last 17 months, has gone from around 88Mbps attainable to 72Mbps, but most is in the last 6 months. It has survived that reduction since December, and is still synchronised at 80Mbps but with around 3dB SNRM.

The best graph I've seen that gives a hint about the random nature of the effect of crosstalk can be seen in a description of vectoring. Look at the graph on page 12 of this document...

The blue crosses all represent the speed seen on various lines at different distances, and the variation between the best and worst is remarkable. For example, at 600 metres the best can get 65Mbps while the worst gets 45Mbps.

Your line is longer than 1km isn't it, so I guess you need to extrapolate to get comparable results.

Here's a before & after set of snapshot graphs:-
http://i.imgbox.com/ackiwNN4.gif

How did you make those? I'd like to try the same!

The really obvious differences are Bitloading, QLN & SNR.
However, I can also see slight deterioration in the Hlog graph, along with slightly increased attenuation as reported via the pbParams data.

The Hlog has changed slightly. As this says something about the underlying copper, it'd be interesting to see if this change has anything to do with time-of-day, weather or seasonal effects. Unfortunately, I guess it is only produced at each resync.

QLN seems to show more noise throughout, which would cause reduced SNRM, and reduced bit-loading. These seem to be consistent, without any notable singularities.

I also notice that TX Power has reduced slightly.

D1 has the same power, but D2 has reduced. Perhaps this is because the modem is using fewer frequencies in D2.

I presume such low speeds no longer require Interleaving, INP & delay setting.

If the lower speeds are caused by increased noise (as they seem to be), then you'd expect wideband interference to carry on in the same way.

If, however, DLM intervened to restrict your speed by banding, then interference can be reduced. However, you'd also see a higher SNRM than 6dB - which you don't.

What might have happened is that all your interference was being caused in tones that are no longer used. Without adverse effects there, DLM can be turned off. But I'm not sure that is the order in which you saw speed reductions happen - DLM turned off before you stopped using the tones.

Now, my question is, can this really all be down to increased crosstalk or is it possible that either something else has gradually caused QLN to deteriorate or is some sort of a line 'fault' brewing?

Wouldn't this be more visible in the Hlog graph? Or by QLN changes at specific frequencies?

I have no idea how many users between the cabinet & my house have broadband connections or even which flavour(s) of DSL they are using.
I also have no idea how to discover if there has been an increase in the number of broadband users, coinciding with the dates I noticed a deterioration.

The interferers can live further away too - their lines just need to run parallel and close to yours before yours branches out.

They're probably not ADSL users (of either flavour) - the QLN graph is being affected way above 2MHz.

Does anyone have any ideas/suggestions?

I don't believe requesting DLM to be reset would have any mileage (even in the unlikely event that such a request would be granted), particularly as Attainable rates are so low & there doesn't really appear to be much in the way of spare SNRM.

I don't think it would make much difference.

Are you still using the new firmware? Perhaps swapping back would say something (or onto it again)
Standard User Bald_Eagle1
(experienced) Mon 13-May-13 23:36:26
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Re: Crosstalk or something else?


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
What was the original estimate for your line?

Back in May 2011 (8c profile) it was 14.6Mb. I achieved around 33Mb sync speed & 32Mb actual throughput for the first month (before 'someone' disconnected my telephone & broadband at the PCP).

When 17a was introduced it went to 24Mb estimated & it is currently 'up to' 30Mb.


DS Attainable rates have gone from 34Mb to 21.5Mb

As Chrysalis points out, the attainable figures when interleaving/FEC is turned on turn out to be artificially high.

So the likely realistic drop is from around 31Mbps to 21Mbps - so you've lost about a third of the line's throughput.

Yes, I've seen that effect, but when DLM has been reset on Fastpath, Attainable rates have been as high as 35Mb & sync speed at around 33Mb.



I think this is still within the bounds of "expected behaviour", even if it isn't very nice to experience.

frown frown


My line, over the last 17 months, has gone from around 88Mbps attainable to 72Mbps, but most is in the last 6 months. It has survived that reduction since December, and is still synchronised at 80Mbps but with around 3dB SNRM.

The best graph I've seen that gives a hint about the random nature of the effect of crosstalk can be seen in a description of vectoring. Look at the graph on page 12 of this document...

The blue crosses all represent the speed seen on various lines at different distances, and the variation between the best and worst is remarkable. For example, at 600 metres the best can get 65Mbps while the worst gets 45Mbps.

Your line is longer than 1km isn't it, so I guess you need to extrapolate to get comparable results.

I'll have a look at that document in due course. Thanks for the link.
My line is somewhere between 1000m & 1100m from the PCP.



Here's a before & after set of snapshot graphs:-
http://i.imgbox.com/ackiwNN4.gif

How did you make those? I'd like to try the same!

Paintshop Pro (very, very old version 5) came with anim.exe for creating/editing animated GIFs.
One simply adds another graphic file into the next frame, confirming the display time & that's it.


The really obvious differences are Bitloading, QLN & SNR.
However, I can also see slight deterioration in the Hlog graph, along with slightly increased attenuation as reported via the pbParams data.

The Hlog has changed slightly. As this says something about the underlying copper, it'd be interesting to see if this change has anything to do with time-of-day, weather or seasonal effects. Unfortunately, I guess it is only produced at each resync.

QLN seems to show more noise throughout, which would cause reduced SNRM, and reduced bit-loading. These seem to be consistent, without any notable singularities.

I also notice that TX Power has reduced slightly.

D1 has the same power, but D2 has reduced. Perhaps this is because the modem is using fewer frequencies in D2.

I presume such low speeds no longer require Interleaving, INP & delay setting.

If the lower speeds are caused by increased noise (as they seem to be), then you'd expect wideband interference to carry on in the same way.

If, however, DLM intervened to restrict your speed by banding, then interference can be reduced. However, you'd also see a higher SNRM than 6dB - which you don't.

What might have happened is that all your interference was being caused in tones that are no longer used. Without adverse effects there, DLM can be turned off. But I'm not sure that is the order in which you saw speed reductions happen - DLM turned off before you stopped using the tones.

Now, my question is, can this really all be down to increased crosstalk or is it possible that either something else has gradually caused QLN to deteriorate or is some sort of a line 'fault' brewing?

Wouldn't this be more visible in the Hlog graph? Or by QLN changes at specific frequencies?

I have no idea how many users between the cabinet & my house have broadband connections or even which flavour(s) of DSL they are using.
I also have no idea how to discover if there has been an increase in the number of broadband users, coinciding with the dates I noticed a deterioration.

The interferers can live further away too - their lines just need to run parallel and close to yours before yours branches out.

They're probably not ADSL users (of either flavour) - the QLN graph is being affected way above 2MHz.

Does anyone have any ideas/suggestions?

I don't believe requesting DLM to be reset would have any mileage (even in the unlikely event that such a request would be granted), particularly as Attainable rates are so low & there doesn't really appear to be much in the way of spare SNRM.

I don't think it would make much difference.


Thanks for your other comments which I will digest shortly.




Are you still using the new firmware? Perhaps swapping back would say something (or onto it again)

No, I had already reverted to the original BLOB in order to compare like for like.
Standard User Chrysalis
(legend) Tue 14-May-13 00:43:09
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Re: Crosstalk or something else?


[re: Bald_Eagle1] [link to this post]
 
Basis for crosstalk is it doesnt look like anything else and yes the QLN.

Remember we on here only have the graph data not JDSU diagnosis etc. On kits forum I even found out yesterday even if a JDSU pass there is other tests that can show failure (you took part in that thread also). But those tests typically arent reported to the consumer, and engineers dont even have to run them on openreach policy.

Whilst its hard to accept I think the most likely thing at the moment is crosstalk.

On my line BT gave me a dedicated dropwire a couple of weeks back and I got all my attainable back, I shot up to 97/39 from the current 68/27 attainable.but they wouldnt let me keep it even tho they had spent time putting it in place, they were just testing and apparently policy only allows 1 dropwire to my building (which has 3 flats). One of my neighbours does have FTTC so now I have pretty much found my cause, both me and my neighbour crosstalking each other. I even had an argument with the openreach manager for my area over the engineers phone for 20 mins to try and keep the new dropwire in place but he wouldnt have it, to him 65mbit and 80mbit no difference.

Since then I have given up and just waiting for vectoring or for my neighbour to cancel/move. My line no longer jumps up and down tho, I supect I am/was affected by other lines also which stopped happening after my first engineer visit. After that first visit the attainable has been on 68/27 is with no variances apart from when they changed the dropwire.

BT Infinity 2 Since Dec 2012
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