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Author Topic: Crazy fault lost 2/3 sync speed.  (Read 5166 times)

burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #45 on: June 29, 2021, 10:35:26 PM »

It is a bit odd two taps would suddenly appear with no intermediate outage?

My two posts (Reply #18 and Reply #20), above, show one example of how that could occur. I won't be surprised if someone comes up with other variants.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #46 on: June 29, 2021, 10:53:28 PM »

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.

Having no recollection of that formula, I went and downloaded both Issue 1 and Issue 2 of TR-197. (I confess to going to sleep after reading about two thirds of Issue 1.)

Carefully searching through both issues of the report, I could not find anything that resembles the formula . . .
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #47 on: June 30, 2021, 01:26:00 AM »

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.

So is that why in the early days they limited what speed you could order so strictly, even though your line technically could easily handle it?

For example initially I was only allowed to order 500Kbit, later they allowed 1Mbit and I even tried for 2Mbit which was refused - but somehow they accidentally processed the order anyway and I did indeed get 2Mbit.

Then once I moved to ADSL2+ with a different company (forgot the name off the top of my head) which had their own DSLAM in the exchange, it was allowed to sync at whatever the line could handle.  When I moved back to Openreach hardware, DSLMax had become a thing and I was forced only a much slower service as I could no longer use 3dB SNR downstream.

Its easy for us to think "oh but it SHOULD handle it", forgetting that the telco have to ensure our lines are blasting out too much interference to other customers.
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #48 on: June 30, 2021, 02:21:11 AM »

Apols for incorrectly remembering the source as the formula has been referenced several times on this forum particularly by wombat over the years.
Source is actually the official JDSU documentation which I'm sure you will have a copy of already. 

In fact if you google the formula, it actually pulls up wombats thread which contains a link to the JDSU documentation in case you dont, and with the lapse of time his post shows why I may have easily thought that the info originally came from TR-197.   I'm glad you made me search so I can re-read the thread again properly and check if he did make any further posts about the topic.

Quote
Bridged Tap
Impact HLog data can indicate the presence of certain impairments.

The HLog graph in Figure 2 shows a dip at Tone #1325 for the first null (approx. 5.7 MHz [1325 x 4.3125 kHz]) of an impairment caused by a bridged tap. The dip Figure 2 that looks like a valley with sloping sides is the tap signature.

The tap length can be estimated with this formula: 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.




Here is a link to *another* document which mentions bridge taps, but this one has a couple of decent examples:
https://www.broadband-forum.org/technical/download/TR-197.pdf

This document is TR-197 from the Broadband Forum, discussing DSL quality factors. The relevant section is on "dual-ended line tests" that are performed in some DSL modems.

Figure 10, page 51, shows the Hlog for a line in 3 states:
- Perfectly normal
- With a 30m bridge tap, first dip somewhere around tone 520. We get to see one further dip.
- With a 200m bridge tap, first dip somewhere around tone 55. We get to see 13 further dips.

Sanity check of the previous formula:
- Tone 520 = 2.25MHz. Tap length = (160 2.25) ft = 71 ft = 22m.
- Tone 55 = 0.24MHz. Tap length = (160 0.24) ft = 667 ft = 203m

The sanity check isn't far off, telling us the formula is a reasonable estimate. In that case, we just measure the first dip, and ignore all the rest.

With gazaai's first dip occuring at tone 164, I calculate:
- Tone 164 = 0.71MHz. Tap length = (160 0.71) ft = 225 ft = 69m

I think that gives us the answer for the total tap length.

That backs up (nearly) just reading data from table 2 (in the original JDSU document) as the only step needed. I don't think you need to perform averages over the extra dips (except for the fact it might give you a better accuracy for where the first dip really was), nor to multiply by the number of visible dips (after all, in reality, those dips go on ad-infinitum).

I also think I know how to read the example in that 1st document better now ... but I'll have to do that in a separate post, likely tomorrow.
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #49 on: June 30, 2021, 04:19:10 AM »

@boozy

Thanks for the further explanation and link which I shall have to read later. :/  It was not my intention to be up at this ungodly hour but circumstance dictates that I am, but it also means Im slow and not the best time to attempt to digest reading anything technical, didn't even get far with wombats thread.

>>  I have no clue why the attenuation is less with the degraged service

It's not uncommon. Noise can and does affect the attenuation.  I've seen faulty/incorrectly fitted filters can add up to 10dB, there's also plenty of examples where oxidised joints have also affected the attenuation, even on my own line many years ago.  RFI, EMI, electrical currents and damaged cables all have the potential to increase the attenuation.   

Whilst the measurement provided by the modem is used to estimate line length, the reality is the modem calculates the attenuation figure based on the difference between the power transmitted and the power received.  The difference between these 2 figures can be affected by a multitude of things, not just line length.  *linky


@Chrys

Are neighbours also experiencing similar severe speed losses or it just you? 
With the fault having other effects such as increasing the attenuation, does this not mean the problem is pretty local - between the cab & home. iirc youre <300m from the cab?

One of my concerns is ignoring what the other graphs and figures are telling us and focusing solely on the bridge tap. 

*was about to link to my own page written many years ago, but then deliberately chose a different source. 
Got a heavy few days coming up with appts,  so bowing out of this convo now as regretfully dont have any more time to speculate or justify my reasoning.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #50 on: June 30, 2021, 09:24:21 AM »

I got no idea on my neighbours sadly, the one I am still friendly with uses virgin media.
« Last Edit: June 30, 2021, 01:49:48 PM by Chrysalis »
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j0hn

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Re: Crazy fault lost 2/3 sync speed.
« Reply #51 on: June 30, 2021, 01:20:09 PM »

It would be a monumental noise source if it was external to OpenReach infrastructure and hit your sync so badly.

Given the Hlog it's almost certainly a defect in the copper pair.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #52 on: June 30, 2021, 02:22:32 PM »

In fact if you google the formula, it actually pulls up wombats thread which contains a link to the JDSU documentation in case you dont, and with the lapse of time his post shows why I may have easily thought that the info originally came from TR-197.   I'm glad you made me search so I can re-read the thread again properly and check if he did make any further posts about the topic.

Thank you for the link back to gazaai's "About my possible bridge tap issue" forum topic which was begun in December 2015. I see that a certain grumpy, old, black cat was also a contributor . . . but after five and a half years all details had been completely forgotten.  :-[
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #53 on: June 30, 2021, 03:28:25 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.

Chrys -- Do you have the raw data, from your modem, in tabular form which should show the Hlog values to four decimal places, please? Something like this:-\

Both boozy's software and my manual method would benefit by using the more precise data. (One decimal place versus four decimal places.)
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #54 on: June 30, 2021, 03:55:17 PM »

I dont think I can find that in my dslstats files, so I just ran the command pasted it into a txt file for you.
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burakkucat

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Re: Crazy fault lost 2/3 sync speed.
« Reply #55 on: June 30, 2021, 05:26:34 PM »

Safely downloaded. Thank you.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #56 on: July 01, 2021, 09:48:12 AM »

I initially wasnt hopeful for getting the reason for the fault as engineer wasnt very talkative but he just rang me with an update and told me the location, so I will see when he comes back if I can get any information on what went wrong.

-----


There was 4 faults he said he fixed, he said two of them the cable was disintegrating when he touched, the other two were joints, all located close to my property he swapped out the cable close to my house.

Looks like he did a DLM reset as well as I am back on fast path.

2 ES in an hour O_o

Since Link time = 59 min 33 sec
FEC:            0               0
CRC:            2               0
ES:             2               0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
HostInitRetr:   0
FailedRetr:     0

« Last Edit: July 01, 2021, 12:01:15 PM by Chrysalis »
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underzone

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Re: Crazy fault lost 2/3 sync speed.
« Reply #57 on: July 01, 2021, 10:35:17 PM »

Your line stats are much nicer now than pre-fault condition. Much higher sync and also attainable speed now  :)
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #58 on: July 02, 2021, 09:31:51 AM »

Its about 5-6 mbit higher now yeah, the socket now has the Master Socket 5C as well.

When I asked the engineer about external damage, he said there was no fault logged for the cabinet affecting multiple customers, but a duct was collapsed he noticed on repair work.  So that theory was not confirmed and it could have all been coincidental.

It is nice on this new socket there is clear icons next to each socket to indicate which is which.
« Last Edit: July 02, 2021, 09:35:25 AM by Chrysalis »
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #59 on: July 02, 2021, 06:05:30 PM »

Careful saying nice things about the 5C, that sort of thing is forbidden round here.  :P
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