Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
   Glossary   Glossary
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Pages: 1 2 [3] 4 5 6

Author Topic: Crazy fault lost 2/3 sync speed.  (Read 4137 times)

boozy

  • Reg Member
  • ***
  • Posts: 128
Re: Crazy fault lost 2/3 sync speed.
« Reply #30 on: June 28, 2021, 12:11:26 PM »

Sorry, but unless I'm missing something, I really can't see another tap and can only see the one continuos wave. It's the regular up and down of a wave that indicates the presence of a bridge tap.  I can only see one distinct regular wave. :(

You can see the first two individual troughs for each of the taps (~150 then ~300 and ~200 then 450) after that the effects of two taps generally bleed into each other.  This depresses the whole Hlog much more than a single tap.
Chrysalis has posted the Hlog data so I'll try to pass it through both a low pass and a high pass filter to separate the two waves - it may not work because of the Hlog depression (you can see a tap much better at the low frequencies as the signal is stronger an the reflection causes more of an effect).

For the first dip in each wave the tap length can be calculated as:
Code: [Select]
        const double speedOfLight  = 299792458.0;
        const double frequencyStep = 4312.5;
        const double propogationVelocity = 0.666666666666; // can be changed for different Wire thicknesses
        const double baseDistance = speedOfLight * propogationVelocity / (frequencyStep * 2); // 2 is for there and back to get the distance
        static double baseLn = Math.Log(baseDistance);

//Above is pretty much a constant

// First Dip:
        answerInM = Math.Exp(baseLn - Math.Log(firstTone*2));

//Multiple Dips:
        answerInM = Math.Exp(baseLn - Math.Log(tonesBetweenDips  / (noOfDdips - 1)));

We're on our staycation (or visiting the relatives we haven't seen in two years to be accurate), but I'll try to find the Butterworth Filter code this evening and separate the tap curves.
Logged

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33004
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Crazy fault lost 2/3 sync speed.
« Reply #31 on: June 28, 2021, 01:30:58 PM »

I do have high power cut back on adsl1 tones, so those tones have always had bitswapping and low bit count.

Yeah, I can recall your PSD spectral mask has always been quite harsh*, but in theory the DSM (Dynamic spectral management) should see your lower attenuation and compensate accordingly.  From your stats in first post it appears to have done so and it's also increased power output in an attempt to increase your bitload.   It's the spikeyness in your QLN which indicates that the low bit load is a result of noise rather than power management.

However its worth bearing in mind that because Openreach uses DSM, then a line which is in fault and has (false) increased atten will be allocated a different mask than if that same line was clear. The DSLAM sees the increased attenuation and assumes you are further from the DSLAM, so will automatically allocate a mask with less PCB in an attempt to increase bit load in the lower band plans (U0,U1 & D1) if applicable. 

If you look closely you will see that your U1 bandplan actually now has a better bitload than before the fault.   Your previous mask allowed max 4 bits and then dropped to 2 bits (typical of some masks within reasonable/mid distance to cab) whereas now it starts max of 5 and drops to 4.  It's the change in your U1 that confirms to me that you are now on a different spectral mask and DSM is attempting to give you more power over those lower band plans in compensation for the increased attenuation.


*It's sometimes possible to take a rough guess at someones distance from the cab and distance from the exchange based on the shaped of their PSD mask. 
I can usually tell the difference in those lines which are near to exchange but some distance from the cab -v- lines which are at a distance from the exchange but close to the cab, based entirely on their spectral mask.

Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33004
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Crazy fault lost 2/3 sync speed.
« Reply #32 on: June 28, 2021, 01:42:18 PM »

You can see the first two individual troughs for each of the taps (~150 then ~300 and ~200 then 450) after that the effects of two taps generally bleed into each other.  This depresses the whole Hlog much more than a single tap.

Thank you for posting further.   Yes I did notice the 150/300 but as I saw no repeat of the pattern..  AND because of the mess going on in QLN/Bitload/SNR over those very same tones discounted it as related to the noise generated in the same tones.  There definitely is something going on in those lower tones indicating noise.

The tap beginning at around 500 was more regular and clearer to see and I would have thought that because those earlier waves only had a width of less than 100 tones it would have made the overall plot look rather bumpy... or at least bumpier than I see with the naked eye.   The curve of 450ish isn't that great and could easily be overlooked as it is, so I didnt do any counting between dips to see how exact the wave was.   I would be interested if you are able to separate the 2 waves please as I don't have anything program wise which takes the raw data to plot specific wave graphs.
 
I accept that its possible they may bleed but without specifically analysing each individual tone, I still cant see that early bump reoccur on the graph alone.  Bearing in mind its causing at least 2 waves every graph line (300 tone divisor), there are several parts of the graph showing a smooth 300 tones eg 3000-3300 showing absolutely no sign of a narrower reflection wave, yet continuing with the wider wave that is around 450/500 tones. 

Is is possible that there could be some sort of damage to a joint or cable which would cause all that HR type noise, but then cause a bridge type effect of a terminal that is not terminated causing the reflection.  Damaged cable?


Quote
We're on our staycation (or visiting the relatives we haven't seen in two years to be accurate), but I'll try to find the Butterworth Filter code this evening and separate the tap curves.

No worries.

TBH I only mentioned the bridge tap because I spotted it, but in Chrys's case with the massive loss of speed it should be a relatively easy fault to find and hopefully clear the same day.
I don't usually bother analysing hlogs in great detail unless in a case which is proving difficult to clear,  as I personally think there's no point speculating if we dont know area/circumstances when its something that has more obvious signs of a fault and that should be easy to fix for an engineer who is on site.   

However as the topic has been brought up at a time in-between flares when there are windows in the day when I'm not in a morphine haze... and because wombat never did get around to publishing his thoughts, then it is interesting to revisit.   Thanks :) 

   
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #33 on: June 28, 2021, 03:21:59 PM »

Thanks for the explanation kitz I get what you are saying now.

I am starting to remember the days gone by when BT would not turn up for afternoon appointments, still no one here yet today.

Thanks to Boozy and everyone else as well.
« Last Edit: June 28, 2021, 03:29:08 PM by Chrysalis »
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 33945
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Crazy fault lost 2/3 sync speed.
« Reply #34 on: June 28, 2021, 04:35:42 PM »

I have historical files including a hlog file full of numbers, is that what you after?

The 00-51 file is from start of june so before fault, 00-17 is today.

It is the raw data that produced the Hlog plot, the second image attached to your post (Reply #2) dated June 25, 2021, 09:46:21, that would be the most interesting to see. I'll take copies of both files and have a look at the data. The first of the two (Hlog-00-17.zip) is probably the one of most interest.
« Last Edit: June 28, 2021, 04:38:58 PM by burakkucat »
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #35 on: June 28, 2021, 05:28:53 PM »

Just be glad you are with AAISP,  this is where they will earn their keep!

Their higher prices are suddenly well worth it when problems like this arise. Good luck!

We will see, they refused to chase up today until the slot is missed and its too late, I have just read focused openreach appointments exist so when they have to rebook this will they do a focused appointment for me or just the cheaper 5 hour slot and of course I cannot even attempt to rebook until tomorrow as they close when the afternoon slot ends.  Also the question of if I will get any compensation.

Might they still turn up? as I lied down they rang once and and I mean just one ring like a test call, wonder if engineer to say he tried to ring to get on his call log.  Or if they will turn up.
« Last Edit: June 28, 2021, 06:18:10 PM by Chrysalis »
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #36 on: June 28, 2021, 05:31:55 PM »

It is the raw data that produced the Hlog plot, the second image attached to your post (Reply #2) dated June 25, 2021, 09:46:21, that would be the most interesting to see. I'll take copies of both files and have a look at the data. The first of the two (Hlog-00-17.zip) is probably the one of most interest.

Thanks, going for a lie down I will maybe check back this evening to see if you have come back with anything. :) 
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #37 on: June 28, 2021, 06:48:14 PM »

Openreach call centre just rang, usual excuses about booking too much work for too few engineers, I could have had wed slot but was afternoon so is now thurs morning.
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

boozy

  • Reg Member
  • ***
  • Posts: 128
Re: Crazy fault lost 2/3 sync speed.
« Reply #38 on: June 28, 2021, 11:25:50 PM »

I checked my figures again and had the lengths embarassingly wrong (one at 60m and one at 80m as opposed to 20 and 30) because I'd put upper and lower limits in the UI. :-[  The maths earlier is correct. That would also mean less depth to the troughs as the signal is degraded more after travelling that for, causing less interference.

Using Butterworth high and low pass filter didn't work brilliantly but it's entirely possibly it's correct (I'm thinking through it with the help of a beer, but may need another).  High Pass is essentially whats left after the low pass is applied (which equates to error with no band pass in the middle).  Its says 40 and 45m, but I think I might need to use a high number of decimal places due to the frequencies being close.

Logged

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 33945
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Crazy fault lost 2/3 sync speed.
« Reply #39 on: June 29, 2021, 12:13:54 AM »

My manual method seemed to show the first four local minima to be --

M1        168
M2        204
M3        380
M4        504

Hence deltas of --

D1        212
D2        300

By lookup in Table 2 (attached to Reply #26, above) and interpolation in the case of D1, I make the two tap lengths to be --

T1        109.3 metres
T2         77.3 metres

Meaningful? Sensible?  :shrug2:
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #40 on: June 29, 2021, 04:11:52 AM »

I am trying to figure out what you guys are doing and I will admit I dont know but it is great, I expect you will turn out to be right if I get told whats happened by the engineer.

I did find this.  It is a bit odd two taps would suddenly appear with no intermediate outage?

https://www.youtube.com/watch?v=JDCc4pkdTLE
« Last Edit: June 29, 2021, 04:20:35 AM by Chrysalis »
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33004
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Crazy fault lost 2/3 sync speed.
« Reply #41 on: June 29, 2021, 05:33:20 AM »

Thanks guys for the further graphs and explanations - appreciated, but some further questions

  • Despite the new graphs, I still cannot see that early narrow 50 tone wave reflecting across the whole spectrum of tones.
  • Would you not expect this narrow wave to make an appearance in the smooth lines of the wider wave.  There are several places where the main wave is smooth enough and wide enough that I would expect it to make an appearance
  • From other graphs, namely SNR, bit load & QLN we can very clearly see that something is causing noise ingress up to about tone 500.  Does this have any bearing on why the wave changed shape after tone 500.

I've never seen a bridge tap wave distinctly change width shape before. It is my understanding that a bridge tap produces a fairly even wave that will continue across the whole spectrum.   It is the frequency at which the first dip occurs which is used to calculate the length of the bridge tap. 

Even though we may primarily use hlog for detection of bridge tap, it does also show up capacitive problems that can cause noise and increased attenuation. 
I have seen certain types of severe noise make an appearance in hlog as one off narrow dips on many occasions before now.  iirc even some of the sample graphs in other learning documentation can show slight noise on hlog of perfect lines or outside of the fault area. 

I'm afraid you've lost me a bit with the more complex calculations and what you are trying to do with the table.  It was my assumption that wombat was doing further investigations to be able to calculate the appx location of the bridge tap.  I may have not gotten what he was trying to achieve, but I have at least once seen him be able to estimate the distance of the fault from the NTE.  I distinctly remember BS congratulating him upon diagnosis of being within 1m.   I never really got much involved in those conversations primarily because I don't have tools to analyse the raw data and was content with wombat saying he would later write up his findings, I just waited for that to appear and only read what was said in public.

I'm not quite sure what the additional table was meant to bring other than I know wombat was doing further investigations into it, but conversely I also pretty sure I do remember him concluding that the first dip was the most important. Since b*cat was actively involved in what wombat was doing with that table, then he will know far more about it than me.

The formula I use is the standard set out by the broadband forum TR-197 namely
Quote
160 Frequency in MHz = Tap Length in feet using the frequency in MHz at the point of the first null, or center frequency of the dip.

  • 4) Going back to the table and how it mentions subdips.  Is that not for graphs that show 2 (or more) recurring dips within a larger wave.  Hence the reason for the term "sub-dips".  I dont have any descriptive documentation other than what is shown, but to me it suggests further notches that show up within what would otherwise be a smooth wave formation.  Chrys's graph shows no sub-dips that I can see, if we exclude that noisy mess up to tone ~500. 
    To explain what I mean about sub-dips, I attach awfully crude diagram where "0" defines the main wave and "1" shows the sub-dips.  Apols for my non-leet paint skills, but hopefully it sufficiently shows what I mean about subdips.



IMHO because of all the noise in tones <500, I'm really not sure if we can draw anything conclusive about those first early dips.   I really cannot see anything where they repeat outside of that noise zone.   The first regular and continual wave I see starts at around tone 500. I deliberately didn't mention a distance in my first post because I was unsure about those early tones and to the naked eye the first visible continual wave only started after that.    However when pushed I think I said about 22m... which uses the TR-197 formula as such

160 (Tone 500 = 2.16MHz) = 74 ft = 22.5m

If we start theorising, based on we know chrys has had no water in his direct area and there was no electricity in a totally different part of the city:   
What if a burst mains caused the collapsed duct and damaged the telephone cable or joint.  The cable and joints are underground and under water. Moisture in the cable is known to cause resistance changes and capacitance faults, which can and do show on the hlog.  What I'm not certain about is if this sort of damage can then also trigger off a bridge tap effect.  It doesn't seem impossible that damage could cause something elsewhere not to terminate properly. 
Other theories seem to ignore everything that is happening in those tones up to 500 - which are abundantly clear in all the other graphs. 

I am interested in what you are trying to do, but it's just that I cannot understand what is going on with the 2x50 tone wide waves that appear to vanish after the noise stops.  If there wasn't all that noise in several other graphs telling us something else was going on, then perhaps I could.   I don't like making assumptions without knowing full facts but with the mention of water problems, its water ingress and damaged cable/joint more making my whiskers tingle - especially from what all 4 of the graphs (QLN,bit-load,SNR & hlog)  are showing us for tones 0-500.  I'm not trying to dismiss anything you say, its just that those early tones are telling me something different is going on.



Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6594
Re: Crazy fault lost 2/3 sync speed.
« Reply #42 on: June 29, 2021, 05:35:52 AM »

The city location isnt that far from me, it where my sister lives, about 5 mins drive.  Not really local to the FTTC cabling but its possible the power grid to her area runs through my area?

Whilst looking at my bitloading to see what kitz told me about my power cutback been removed from upstream, I noticed U2 seems less affected and is achieving higher tones but I guess thats down to less noise.

I will speculate that assuming my line gets fixed, there may be other pairs still damaged, and since there is now different power masks been used across different lines, some weird crosstalk effect may happen.
« Last Edit: June 29, 2021, 05:45:25 AM by Chrysalis »
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33004
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Crazy fault lost 2/3 sync speed.
« Reply #43 on: June 29, 2021, 06:30:27 AM »

Openreach call centre just rang, usual excuses about booking too much work for too few engineers, I could have had wed slot but was afternoon so is now thurs morning.

Damn.   Thats annoying that you have to wait until Thurs.   I'm hopeful though with it being such an obvious loss in speed that the fault can easily be found.

Whilst looking at my bitloading to see what kitz told me about my power cutback been removed from upstream, I noticed U2 seems less affected and is achieving higher tones but I guess thats down to less noise.

I will speculate that assuming my line gets fixed, there may be other pairs still damaged, and since there is now different power masks been used across different lines, some weird crosstalk effect may happen.

DSM has very obviously given you a different power mask (PSD mask).  The DSLAM has seen the increase in attenuation and thinks that you are further from the cab than you really are.   

atm its working in your favour on the upstream and allowing more bits to load in your lower tones than they would normally.  Because most of the noise is <500 its only really of the most advantageous to your U0.   The DSLAM is trying to give you more power to keep your speed up.  If you notice your power figure has also changed in your stats.   
Unfortunately your downstream cant benefit because of all the noise that is happening in D1, but when I looked and compared old and new the other day, even the D1 shape had slightly changed.   So yeah the DSLAM has noticed the noise and trying to keep you connected by increasing your SNR > bitload.   If you were still on your old PSD mask, then your sync speed would be a bit lower than it is now.

Once your line gets fixed then the DSLAM will notice and DSM will immediately put you back on your old mask. 
 
Shouldn't really make much difference to crosstalk.  The whole idea of the DSM is to apply masks based on individual line conditions.   Borked lines are under performing so even though they may be on a 'better' mask, they are too sick to take full advantage of it, so wont be able to give you any more crosstalk issues than they would under normal circumstances. 

Thats the beauty of Dynamic Spectral Management compared to the old system;- the DSLAM only allows longer lines more power...  but if a line is under performing it can also ramp up the power for those lines which need it. In days gone by there were only a handful of masks and you stuck with what you were initially allocated.  Now there's many that can change each and every time you sync up depending upon line conditions.
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

boozy

  • Reg Member
  • ***
  • Posts: 128
Re: Crazy fault lost 2/3 sync speed.
« Reply #44 on: June 29, 2021, 08:06:20 PM »

I wasn't going to post this particular reply because the bit in bold is confusing me, but I can't think of anything better than 2, or 4 (2 on each leg), taps - so I'll throw it out and hopefully someone will be able to explain it.

The two figures I was using are 150 and 200 (rough estimates of the two first dips equating to 58m and 77m) BCat went more accurately to 168 and 204.  How confident would I be about any of those...  well I wouldn't bet on any numbers (as I've thought too much about it). The biggest head melter is that the Hlog from the impaired service looks like it would be from a much shorter line than the original even without being fixed :)

The first dips are likely to be best as you get into interference in the higher bins. Additionally if the tap is long then there are no "dips" just a general depression (https://www.analog.com/-/media/images/analog-dialogue/en/volume-34/number-1/articles/vdsl-technology-issues-an-overview/vdsl-fig-03b.gif?la=en&vs=1).  What happen for two taps... not sure but I'll come to that.

A VDSL modem has in effect 4096 56K modems each with a different frequency (bin/tone). 
Taking just one 56K modem:  data is transmitted on the particular frequency it "owns".  The data goes down the conductor until it reaches the tap.  At that point the waveform goes down the tap and simultaneously on to the receiver.  The waveform travels down the tap, slightly degrading as it goes, and reflects off the end.  After reflection, where the resulting waveform will fall somewhere into the range of having destroyed itself to reflecting almost perfectly, what remains will travel back up the tap and crash back into waveform at the tap start.  The longer the tap, the less the effect of the crash (degredation) and the same for the worse reflection.

With two taps I think something like two source interference will also be happening (http://www.physics.louisville.edu/cldavis/phys299/notes/lo_interference.html), light also being a transverse wave. I can't picture what will happen, but messy would be my guess.

I think that was a long way of saying I don't trust any of the period measurements, but would go for 168 and 204 as the best bets for first dips(I used 150 and 200 as mine originally).  I have no clue why the attenuation is less with the degraged service - that makes no sense at all.
Logged
Pages: 1 2 [3] 4 5 6
 

anything