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Author Topic: Crazy fault lost 2/3 sync speed.  (Read 7190 times)

underzone

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Re: Crazy fault lost 2/3 sync speed.
« Reply #15 on: June 26, 2021, 12:57:04 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!
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #16 on: June 26, 2021, 02:27:13 PM »

Quote
I also remember the results from PlusNet e.g. show your DLM profile, whilst the one provided by AAISP doesnt show it.

I seem to remember something about there are different tests that can be run depending upon permissions and which section of the CP is used.   I haven't actually seen this myself, its just something Ive seen mentioned in conversation with someone who does have access.  The info certainly looks cut down when compared to the full version.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #17 on: June 26, 2021, 03:25:45 PM »

Yeah that may be the case.

Anyway engineer is now booked for Monday afternoon, a lot sooner then I expected given covid etc.

I have a 3 week wait to get water supply back.  To put into perspective of waiting times.

I will be very curious if I find out what happened here, having water fail, a power cut in another part of city and this happen all in close proximity seems like at least 2 out the 3 might be related.  The power cut I was told was between 7 and 8 not an exact time given.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #18 on: June 26, 2021, 03:50:53 PM »

Here is a scenario that might fit the facts . . .

A large diameter, high pressure, high flow rate water main develops a leak / bursts. The escaping water washes out significant quantity of sub-soil. A road or pavement subsides. The subsidence damages other underground plant -- sewage, electricity, gas, telecommunications. To re-establish telecommunications, Openreach lay a temporary diversion cable around the hole. That diversion cable is crimped onto the existing cable at appropriate access points before the damage at hole. There are now two shortish-length bridge taps on each and every pair in the cable. Hence the abnormality in the Hlog plot for your circuit.

----- existing cable ----- damage ----- existing cable -----
                               |                   |
                               \                   /
                                 \                /
                                  |              |
                                   ------------
                                Diversion Cable
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #19 on: June 27, 2021, 04:02:07 AM »

The first part sounds viable, not sure about laying a temp diversion though as would that not involve a short period of downtime or which there didnt appear to be any.  I'm with you on water could cause u/g duct to collapse and a diversion cable causing bridge taps though and that part of the theory is probable. 
 
I think it was wwwombat who used to be quite good at having a stab of location from home based on hlog first wave dip and distance between the dips..  which is something the JDSU does automatically based on hlog and (real)SNR.  As far as I can make out, those wavedips run quite evenly throughout almost all of the tones, but may possibly start at around tone 450ish. 

Below tone 300 is rather messy on the QLN - this also shows up in the Bit loading and real SNR.  Look how many tones are knocked out at around 120-300.   However that alone isnt sufficient to account for the total amount of speed loss.   Something is causing a load of noise in those lower tones...  and its then causing a reflection type wave on the hlog in the higher tones.   

I wouldn't like to guess what could be causing that, but its certainly not impossible for water to cause duct collapse and damage to other cables.  Not going to spend any more time theorising as I'm sure something like this would be picked up by a JDSU ,  but it would be nice to know what the engineer says what the cause was.


However, I have almost convinced myself that the GEA run by AAISP doesnt include the full suite of tests because (1) We can see what looks like signs of a bridge tap in hlog with the naked eye*  and (2)  It should have failed the downstream rate assessment test.



*Of all the tests run, the bridge tap test is usually quite sensitive; There's many a time I've seen FAIL reported when (a) there's hardly anything to see on hlog or (b) it gives a false positive.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #20 on: June 27, 2021, 09:36:04 AM »

. . . not sure about laying a temp diversion though as would that not involve a short period of downtime or which there didnt appear to be any.

There are three-way crimps which have a slot and, thus, can be placed over a contiguous length of wire. Such crimps can be used in those cases where a disconnection is to be avoided.  :)
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boozy

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Re: Crazy fault lost 2/3 sync speed.
« Reply #21 on: June 27, 2021, 12:21:28 PM »

There are two taps, both between 20m and 30m long, going from the Hlog.  BCat seems to be the winner. 

I don't think you can figure out how far away they are - but if someone knows I'd love to find out.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #22 on: June 27, 2021, 08:54:59 PM »

I did look at existing works for severn trent near me, incase its already planned.

There is a lot, seems they have a lot of faults, but none seem to be on the route I think my cable takes and none were mentioned for my street specifically, which is why I reported a new fault to severn trent on saturday.

I will of course let you guys know if I get anything useful from the engineer.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #23 on: June 27, 2021, 11:45:26 PM »

There are two taps, both between 20m and 30m long, going from the Hlog.  BCat seems to be the winner. 

b*cat waves a paw.  ;)  I took a look at the second of the Hlog plots shown, above, and it was very much a case of "tingles in the whiskers" telling me that it was not a single tap.
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #24 on: June 28, 2021, 12:00:49 AM »

There are three-way crimps which have a slot and, thus, can be placed over a contiguous length of wire. Such crimps can be used in those cases where a disconnection is to be avoided.  :)

Ah .. are you saying that they may have in effect cut into the routing that Chrys's line takes to make a repair to another site?   I think I discounted that because I could see how that would then make Chrys's routing longer.   I was working of the assumption that because Chry's line didn't actually go down, then his routing was unaffected.  I couldnt see how that if a mains collapsed elsewhere and unrelated to him... couldnt see why his line length would suddenly get longer.
   
I did try then envisage various routings in my head but my fingers werent keeping up at this point and I thought not worth bothering about because there were too many things we didnt know such as where the power cut was could be right over the other side of the exchange and nowhere near him anyhow.   If Openreach have spliced into Chrys's routing I will imagine it will just come back up right again when Openreach get around to sorting whatever is wrong elsewhere in his city.   I hope it isnt that, because it could take ages to be able to fix...  and they may not even be able to do anything about it tomorrow.     
It took best part of a year to fully fix the collapsed duct in my daughters street and even after it was supposedly fixed, the line never ran as good again as it did previously..  and it was a partial reason for them ditching g.fast.
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #25 on: June 28, 2021, 12:17:38 AM »

There are two taps, both between 20m and 30m long, going from the Hlog.  BCat seems to be the winner.

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. :(

I'm not sure what is going on at apprx tone 150 but since that narrower wave bump does not recur across the whole band-plans plus it also coincides with a load of noise in the same tones then that to me would indicate something else.... 

... and whilst there is something else happening at <tone 300 but its not just solely visible on the hlog.   At this point we need to switch to QLN, bit load & SNR where we can see something noise related going on here.  Whatever it is, it is showing in the real SNR and has caused zero bit loading up to around tone 300 which will amount to a chunk of his speed loss.  It's also showing in the QLN so its a sure assumption that its not a tap but something more like a HR fault is causing an issue at those lower tones up to around 300-350ish.

The first (repeating) dip that I can make out occurs at around tone 500ish / 2.16MHz, which I think equates to a tap length of about 22m.

Quote
I don't think you can figure out how far away they are - but if someone knows I'd love to find out.


I think wwwombat worked out something.  I recall him being quite accurately being able to diagnose one particular fault to within 1m of how far the fault was located from the NTE.  He managed to do this on more than one occasion. He did say he was going to write more about it, but I think it was one of hose things he never got around to. :(

b*cat may have more recollection because they were iirc talking about the formula in PMs too.  About the only other thing I can recall is that he didn't place too much importance on the number of dips,  but more to do with the frequency at which the first repeating dip occured.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #26 on: June 28, 2021, 01:16:09 AM »

I think wwwombat worked out something.  I recall him being quite accurately being able to diagnose one particular fault to within 1m of how far the fault was located from the NTE.  He managed to do this on more than one occasion. He did say he was going to write more about it, but I think it was one of hose things he never got around to. :(

b*cat may have more recollection because they were iirc talking about the formula in PMs too.  About the only other thing I can recall is that he didn't place too much importance on the number of dips,  but more to do with the frequency at which the first repeating dip occured.

We, wwwombat & b*cat, used a table, shown in an JDSU Application Note, that allowed an estimation of the length of a bridge tap to be calculated. If Chrys still has the raw data, from which the above Hlog plot was generated, it would be interesting to have a play with the data. I also know, from prior PMs, that boozy would also be interested in seeing the raw data.  ;)
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #27 on: June 28, 2021, 01:26:15 AM »

Ah .. are you saying that they may have in effect cut into the routing that Chrys's line takes to make a repair to another site?

I have worked on the assumption that the Openreach ducts were left hanging over the hole and the cable(s) therein were not severed. To allow a proper reinstatement of all the services and to allow the hole to be filled in, an appropriately sized diversion cable was connected either side of the hole. Using three-way crimps, the live services could be transferred to the diversion cable. Then the unsupported duct(s) could be cut away, the cable(s) therein severed and thrown to either sides of the hole. Those two ends of the original cable(s) would then show up as two bridge taps on each and every pair.

However all of the above is just pure speculation based upon what Chrys has reported.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #28 on: June 28, 2021, 02:31:20 AM »

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

Also as you said kitz I do fear there will be no fix tomorrow (later today, really need to go bed), as I expect this could be damage caused by another utility company, just a wait and hope.

ps. my water is back to normal now.
« Last Edit: June 28, 2021, 02:50:53 AM by Chrysalis »
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #29 on: June 28, 2021, 02:35:17 AM »

We, wwwombat & b*cat, used a table, shown in an JDSU Application Note, that allowed an estimation of the length of a bridge tap to be calculated. If Chrys still has the raw data, from which the above Hlog plot was generated, it would be interesting to have a play with the data. I also know, from prior PMs, that boozy would also be interested in seeing the raw data.  ;)

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.
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