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[burakkucat]

Having downloaded both graph sets, I then displayed them as a continuous slide show and the high frequency degradation was abundantly clear.

If Mr Pag (Razpag) was still "one of us", I would ask for his opinion on my diagnosis of a possible HR joint. Clearly there is something amiss with the copper pair between the NTE5/A (in the Aerie) and the DSLAM (in the fibre cabinet, situated on Heywood Lane).

Another OR engineering visit will have to be arranged by PlusNet, methinks.

[waltergmw]

Hi Paul & BKK,

It also seems clear that an enhanced escalation procedure is required which might well require technical input from BT Wholesale specialists.
Given the limited DSLAM technical training BT openreach seem to be given, it seems quite unreasonable that a BT O engineer is expected to be able to solve this type of intermittent fault.
At a practical level, how can a BT O engineer interpret the diagnostic data presented to him ?

Without additional help this sort of problem could go on for many months (if not to Infinity) and at significant expense and inconvenience to all concerned.

Kind regards,
Walter

[silversurfer44]

Well, not to make to light of this fault it seems to fall into the kind of fault finding I did for the last twenty years of my working life. No i am not qualified nor extensively knowledgeable of the Telecom industry.
Having said that I have read through this post and deciphered that there is no apparent fault on the copper wire from Paul's house to the terminal cabinet for the copper run. There appears to be no fault from the exchange to terminal cabinet for the fibre. If I understand this correctly there must be a point where the copper joins the fibre. Using my experience as a fault finding engineer and an experience I had with a particular electrical fault, I would think (suggest) the problem lies in the area where the two meet up.

The scenario I was faced with was a dead photocopier. There was correct electrical readings throughout the machine, no blown fuses etc. There was 240 volts coming from the wall socket, the plug was wired correctly. The answer was obvious that the socket was faulty in some way. I had to insist that some-one from the company do a visual check on the socket wiring. Lo & Behold it was found the Neutral wire was not secured into the back of the socket.

I trust one can see the resemblance to Paul's fault, all the connection readings are correct, yet there is this HR fault. Has any of the engineers done a physical check on where these two cables join. If it's not a physical join, but a piece of equipment that does the joining then if it has not already been replaced then I would place some money on this piece of equipment.

[waltergmw]

Hi SS & Paul,

If my memory has not disappeared entirely, I recall that BT O did a "Lift & Shift" in the FTTC. If so, perhaps with PN's confirmation that a new port is now in use, that should have eliminated anything within the link cables and the FTTC.

Assuming that BT Wholesale will be reluctant to intervene, one of the few remaining options for BT O are to investigate the D side line to Paul's house.
Drop wire 12 should be used to replace the entire house-end wiring together with a new NTE as well. That must be followed with an new pair connected back to the PCP.

Perhaps if PN are also fed up with the time this fault is consuming, they might escalate the matter via their BT W contacts to ensure the problem is tackled completely ?

Kind regards,
Walter

[Bald_Eagle1]

Hi SS & Paul,

If my memory has not disappeared entirely, I recall that BT O did a "Lift & Shift" in the FTTC. If so, perhaps with PN's confirmation that a new port is now in use, that should have eliminated anything within the link cables and the FTTC.

Assuming that BT Wholesale will be reluctant to intervene, one of the few remaining options for BT O are to investigate the D side line to Paul's house.
Drop wire 12 should be used to replace the entire house-end wiring together with a new NTE as well. That must be followed with an new pair connected back to the PCP.

Perhaps if PN are also fed up with the time this fault is consuming, they might escalate the matter via their BT W contacts to ensure the problem is tackled completely ?

Kind regards,
Walter

Hi Walter,

Yes, the lift & shift was supposedly done 14th September.
Speeds did marginally improve for a day or so, but only to about 22Mb (still 10-11Mb short of the initial speeds).
So it didn't appear that I was being provided with a "brand new" installation as promised.

The SFI engineer even phoned Plusnet to query why on earth I was looking for more than 20Mb because I was already achieving it at the time.
Plusnet had to explain to him that FTTC is an "up to 40Mb" service, not ADSL2+ speed.

I have still not received any confirmation that at least 40Mb is available at or near the cabinet, or that my BT profile had been reset to 40Mb for the training period to start all over again.

I saw the modem resyncing when the engineer did the L & S, or whatever it was that he did.
Within seconds, I had conducted a speed test that showed nowhere near 30Mb, never mind 40Mb.
Within minutes of the engineer leaving I had reconnected the unlocked modem & was only achieving an Attainable Rate of 25124 K & a Line Rate of 25067K.

If you also recall, the "double jumpering" was supposedly tracked down by the use of TDR testing, but NOT retested after the double jumper was removed as "it wouldn't be necessary as the fault has been fixed".
Maybe the double jumper was contributing to the issues, but not the major factor?
Whenever I "fix" anything, I test afterward to make sure there isn't still some other underlying fault.

I have asked Plusnet's Bob Pullen to do whatever he can to escalate this issue accordingly for a quick & satisfactory resolution once & for all.

What is Drop wire 12? I haven't heard that term before.


Paul.

EDIT:
Found it:-
http://www.caledonian-cables.co.uk/Telephone/Indoor/CW1406.htm

[attachment deleted by admin]

[waltergmw]

Hi Paul,

I suggested drop wire 12 as a replacement as it has larger 0.9 mm dia wires and as a single pair there is no possibility of a second pair affecting it.

Remember that the up to 40 Mbps is the modem sync rate. On one good FTTC service in Guildford, at about 100 m from the FTTC, that line achieves an average throughput of 37.1 Mbps which perhaps should be recorded as the maximum practical throughput speed.

Although there is more variation in throughput speeds, my Virgin Media service usually achieves around 95 Mbps which is undoubtedly the better solution where VM have installed their services. Sadly that is not everywhere !

Kind regards,
Walter

[silversurfer44]

Wouldn't it be a tad expensive to replace all the cabling?
Also quite disruptive?

If the cabling from the pole to cabinet runs via ducting then I could see a replacement as a solution. If the cable is via some other means well!!!

PS I could look up the acronyms but for what I will be posting?

[asbokid]

Hi Paul..

I think Walter has nailed it.... 

My layman's understanding of your line stats graphs is that they suggest that something is physically wrong with your loop.

I just made a blog post about the four metrics in the graphs (BITS, SNR, QLN, and HLOG).[1]

Perhaps most interesting in your case is your chart of Hlog(f). I believe it illustrates the problem.

Hlog(f) is a logarithmic measure of the channel insertion loss.  In other words, it measures loop attenuation at individual sub-carrier frequencies across the band-plan spectrum.

The plot of Hlog(f) needs to be read upside-down. It is actually inverted, insofar as the lowest point of the red zone charts the attenuation reading for a given frequency. (An attenuation measurement of -96dB means the data is not available or is out of range).

We can identify the following characteristics of the attenuation on your loop from Hlog(f).

The lowest utilised sub-carrier in the lower D1 downstream band is DMT ~#36 which is transmitted at ~150kHz.  (Remember vDSL Profile 8c uses 4.3125kHz channel spacing, so 36 * 4.3125 = 150kHz.)

In your 'good' Hlog graph, a channel insertion loss of -6dB was measured at 150kHz.  In the 'bad' Hlog graph, a channel insertion loss of -12dB was measured at the same frequency.

The highest utilised sub-carrier in the lower D1 downstream band is ~#690. This tone is transmitted at ~3.0MHz. In the 'good' graph, a channel insertion loss of -17dB was measured at that frequency.  However, in the 'bad' graph, attenuation at 3.0MHz has jumped to -45dB.

In the second downstream band (D2), the lowest tone is ~#1195. This tone is transmitted at ~4.9MHz. The loop attenuation measured at the frequency in the 'good' graph was ~-25dB. However, in the bad graph, the measurement was ~-65dB.

The highest utilised tone in D2 is DMT #1625. It is transmitted at ~7.0MHz. The 'good' graph shows loop attenuation of ~-27dB at that frequency, whereas the 'bad' graph shows a loss of ~ -75dB.

So in the period of time between the data collection for those two graphs, your loop mysteriously developed a high attenuation profile across the whole bandplan spectrum.

The attenuation measurements by themselves are not that useful. The sensitivity of the ADSL transceiver units will actually determine whether the signal at a given frequency can be recovered.

What's more important for diagnostic purposes is the slope of the Hlog graph which takes the form of an exponential decay function.  Characterising the Hlog graph is not straightforward. Since the ordinate scale shows negative decibels you could call it an exponential growth function as attenuation grows as the frequency gets higher.

It would be useful to use non-linear regression (curve fitting) to discover the parameters of the attenuation function for a given loop.  That's what I am trying to develop as part of the port of the dmt tool for use with vDSL connections. I see that Huawei Corp has patented a couple of ideas in that sphere. If anyone would like to collaborate on an open source project to do this, please contact.

Once the parameters of the attenuation function are identified, it could be superimposed upon the 'classic' attenuation functions for the typical loop, enabling diagnosis by comparison.

For example, the parameters of the attenuation function for a (faultless) single segment twisted pair constructed to BT cable specification CW1128 - class 1 solid annealed 0.5mm plain copper conductors with cellular polyethylene (CEL-PE) insulator - will be well known to the egg-heads at Martlesham Heath. 

They will also know the (higher) attenuation profile of the aluminum twisted pairs that were used as a substitute when copper prices soared at the hands of the City gangstas in the 1970s.

Here are some plots of the attenuation functions for twisted pairs using various wire gauges (AWG24 has 0.5mm conductors). The plots were taken from [2] and [3] and are only meant for illustrative purposes. The units of measure and the graph scales are all over the place. To develop anything out of it, we need the parameters of the functions to plot those graphs. Then they could be used for various comparisons.



According to a European patent filed by Huawei in Sweden, the attenuation profile of a loop can be used to accurately estimate its length and to gauge its physical condition.

Enough rambling!

Cheers,
A

[1] http://huaweihg612hacking.wordpress.com/2011/10/01/measuring-line-characteristics-on-the-huawei/
[2] http://www.cc.gatech.edu/classes/AY2005/cs4251_fall/class5.ppt
[3] http://www.serialphy.com/attenuation-chart-24-awg-wire.html

[Bald_Eagle1]

Hi Paul..

I think Walter has nailed it.... 

My layman's understanding of your line stats graphs is that they suggest that something is physically wrong with your loop.

I just made a blog post about the four metrics in the graphs (BITS, SNR, QLN, and HLOG).[1]

Perhaps most interesting in your case is your chart of Hlog(f). I believe it illustrates the problem.

Thanks asbokid for your clear explanation & links to sources of information.

I could see what appeared to be wrong with my connection, but just couldn't put it into plain words.

Now, as my connection has delivered much higher & stable speeds of 30Mb+ throughput in the past, it appears that I simply need to get BT (via my ISP & phone provider Plusnet) to find the fault(s), somewhere physically in my connection & fix it/them once & for all.

That sounds very simplistic, but in reality....................?
I am but one small voice in a mighty organisation's service provision.

The intermittent nature of this issue (e.g. the dramatic downturn over the last few days of unseasonably hot weather) is understandably causing some diagnosis difficulties & appears to have an incredibly detrimental effect upon how DLM automatically restricts my speeds (assuming at least 40Mb is really being delivered to the cabinet where the DSLAM & DLM equipment is installed.

BTW, all the modems have stayed quite cool to the touch throughout these issues, so there would appear to be no point in replacing them just as a matter of course.

I have pointed various Plusnet staff members to this thread & requested the matter be escalated accordingly, so hopefully the additional explanation/information you have now provided will go some way in helping to speed matters along.


Paul.

[Bald_Eagle1]

Wouldn't it be a tad expensive to replace all the cabling?
Also quite disruptive?

If the cabling from the pole to cabinet runs via ducting then I could see a replacement as a solution. If the cable is via some other means well!!!

PS I could look up the acronyms but for what I will be posting?

Hi Silversurfer44,

The cable from the nearest pole to my home is overhead, as is much of the cable from the cabinet.

One of the engineers did mention that it is steel reinfoced though.
I wasn't sure if he meant just the main runs, or from the pole to home, or both.
The cable from the pole to home doesn't look very thick though.


Paul.

[silversurfer44]

If you look at the cable from your home to the pole looks black then it will be the reinforced variety, if it looks grey and similar to a twin flex for a lamp then it is not the reinforced.
The two are very distinctive, I have both running to my house and can see the difference.

I have just been looking back through your novel and noticed the question of aluminium was never resolved, I think it finished on a maybe. Regardless of that I do believe the answer is in pure simplicity of good and bad connection/wiring. It would appear as the stare in the face type fault is being overlooked.

I applaud asbokid in his knowledge and depth of explanation, however it reminds me of the tale of the mathematician and the jar of pickles. The mathematician could tell you the perimeter of the lid, the inside area, the thickness absolutely every dimension you could think of, but he couldn't tell you how to get the lid off to get to the pickles.
I am not casting aspersions or anything asbokid, just that throughout this riveting novel the same thing has been done, and, I think the powers that be are still doing it.

[waltergmw]

HI Paul,

Just to add a little to SS's comments, a black drop wire contains steel catenary wires as well as the copper twisted pair(s) you'll see from the cable spec you found whereas BT's multicore distribution cables have a separate steel wire incased in a much smaller diameter PVC envelope. The picture in this link shows a BT pole demolished by a buffoon behind the wheel ! You can see where the catenary wire has been pulled out of one 50 pr cable and another through-cable where BT obviously ran out of serviceable pairs. The die-cast pole support has been forced through nearly 90 degrees as the cables are supporting the pole instead of vice versa. The line clamps only bite into the catenary cable and not the larger twisted pair one.

I am hoping that BT O might replace your drop wire as it is relatively inexpensive. If they do perhaps you could ask the engineer to leave the catenary wires just outside the NTE so you could experiment by earthing them to see if that has any screening effect.

http://www.scribd.com/doc/67277255

Kind regards,
Walter

[Bald_Eagle1]

If you look at the cable from your home to the pole looks black then it will be the reinforced variety, if it looks grey and similar to a twin flex for a lamp then it is not the reinforced.
The two are very distinctive, I have both running to my house and can see the difference.

I have just been looking back through your novel and noticed the question of aluminium was never resolved, I think it finished on a maybe. Regardless of that I do believe the answer is in pure simplicity of good and bad connection/wiring. It would appear as the stare in the face type fault is being overlooked.

I applaud asbokid in his knowledge and depth of explanation, however it reminds me of the tale of the mathematician and the jar of pickles. The mathematician could tell you the perimeter of the lid, the inside area, the thickness absolutely every dimension you could think of, but he couldn't tell you how to get the lid off to get to the pickles.
I am not casting aspersions or anything asbokid, just that throughout this riveting novel the same thing has been done, and, I think the powers that be are still doing it.

Hi SS44,

The cable from the pole is black.

Regardless of aluminium or not, I had a high(ish) speed & stable connection for a while.
Now I don't (& haven't for quite some time now).

Please Mr. BT Man, fix it - "Simples".

Asbokid has managed to get the lid off the modem, & we are at last able to see our pickles / connection statistics.
Prior to that point, everything was just assumptions & guesswork.

It is all asbokid's fault for not unlocking the modems in time for me to have gathered my stats immediately following FTTC's installation  .
I would at least have been able to compare my current stats against the "good" stats that BT and/or Plusnet do not possess (or so they tell me).

[asbokid]

The cable from the pole is black.

Regardless of aluminium or not, I had a high(ish) speed & stable connection for a while. Now I don't (& haven't for quite some time now).

Please Mr. BT Man, fix it - "Simples".

Asbokid has managed to get the lid off the modem, & we are at last able to see our pickles / connection statistics.
Prior to that point, everything was just assumptions & guesswork.

It is all asbokid's fault for not unlocking the modems in time for me to have gathered my stats immediately following FTTC's installation  .
I would at least have been able to compare my current stats against the "good" stats that BT and/or Plusnet do not possess (or so they tell me).

I was looking again at your graphs. The plot of Quiet Line Noise shows an average of ~20dB more noise between the 'good' and the 'bad' graphs.  The data readings for QLN are taken during the xDSL initialisation and training phase and before the xDSL connection is active. The readings may also be re-taken at any point thereafter at the request of either the CPE modem (known as the ATU-R) or the DSLAM (the ATU-C).

The steep narrow 'spike' in the noise measurement around tone #250 (1MHz) is very distinctive.

Burakkucat already alluded to the likelihood of a high resistance joint or splice being the physical cause of your line problem.  If that's what it is,  then perhaps it's aggravated by environmental conditions - humidity/water ingress, elevated ambient temperature etc..

Below are some Application Notes by Chris Dunford from EXFO, an expert in telecoms test and measurement systems.  His Notes contain a number of oscilloscope traces from Time Domain Reflectometry tests on faulty lines. The traces show the effects of each type of fault.[1]  Of course, all we can do with the Huawei is analyse the magnitude responses in the frequency domain.  How they can be correlated with the TDR results (if at all), I don't know 

The document linked at [2] is the Masters Thesis of Matthias Ernell, a postgraduate at KTH, the Royal Institute of Technology in Stockholm. The title of Ernelli's work is "Loop Qualification for VDSL2". At the time he authored the document (2008), Ernelli was working for the Swedish telco, Telenor and must have gained a lot of wisdom and inside knowledge from that employment.  The thesis is really well written, and perhaps the best technical document I've ever read on xDSL.  Chapter 3 is dedicated to Loop Measurement, the characterisations that our graphs try to reproduce.

Cheers,
A

EDIT Link to Application Notes containing TDR scope plots; Corrections to comments about the 'spike' around 1MHz in Paul's QLN graph; Reference to Ernelli's work

[1] http://documents.exfo.com/appnotes/anote168-ang.pdf
[2] https://eeweb01.ee.kth.se/upload/publications/reports/2008/XR-EE-KT_2008_003.pdf

[Bald_Eagle1]

So in the period of time between the data collection for those two graphs, your loop mysteriously developed a high attenuation profile across the whole bandplan spectrum.

@ asbokid,

Just to clarify the origin of the graphs, the "bad" one is mine from 2nd October & the "good" one is from another user who is achieving the full 40Mb DS & 10Mb US.

My US is capped at 2Mb with my Plusnet package.

I don't have modem statistics from when I was achieving over 30Mb DS throughput, but to have achieved that level of throughput, my line's statistics & therefore quality MUST have been much better than they are currently.

The only other explanation would appear to be that maybe BT had not implemented their 40Mb DS cap during, & a little beyond the 10 day training period.
If that was the case, my throughput speeds would have been attenuated down from over 50Mb to the typically 32-33Mb that I achieved.

The latest visiting engineer had that theory, but he did admit that it was only his personal theory, unconfirmed by BT.

However, as Plusnet have confirmed that their speed cap is 40Mb from the outset & also confirmed that BT's cap is 40Mb from the outset, the current statistics would appear to confirm some sort of resistance/loss of signal (or speed capping) in my connection that wasn't previously present.

I have attached graphs from immediately following a recent lift & shift operation, when I achieved around 21-22Mb throughput for a short while.
It is thought, but still unconfirmed, that 40Mb was available for my connection at the cabinet following the L & S.

So, the remaining question is what can BT now do to locate the line "fault" & to reinstate the quality of my connection to its original standard.

Finally, as the reported SNRM level was high earlier this morning, I forced a modem reboot.
However, the DS rate for Path 0 is now only 14999K, but the US rate has gone back to 2000K.
This is from an Attainable Net Data Rate of 24012K DS & 6966K US.
This now gives this throughput & suggests BT's DLM capping of their basic 15Mb:-



Confirmations from BT's online checker & another online checker that accesses BT's systems are that my current BRAS rate (IP Profile) is: 12674 k


Paul.

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