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Standard User IranianGiraffe
(regular) Tue 10-Jun-14 15:06:17
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line issues???, possible bridge tap


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Hi all,

For years I had issues with my ADSL connection in that the line went down 99 times out of 100 when the phone rang, I had around 20 engineers come round to try and fix the issue and they never did, lowering the upstream to 448 made it a lot better but it still did it most of the time (prob 8 out of every 10).
At the end of last year thanks to BDUK funding my cabinet was upgraded to fibre and when I first connected I was able to get 53meg download and 15 or so upload.

For the first week I was able to get 53meg it then went down to 46meg and stayed around that for another 3 weeks and then took a bit of a nose dive to 34meg (engineers were called out but found no issues and even though I could prove I had 50+meg to begin with recorded sync and speed tests from ISP the engineer said that they must of been incorrect as there was no way I could expect to get anymore than 30meg but it shouldn't fall below 30).

Anyway a few weeks later It then fell under 30 and I then decided to get myself a HG612 modem so I could unlock it and look at the speeds, since doing that my line went from having interleave to removing it and in turn ended up giving me some speed back (been around 32meg down / 8 up for a few months.
I realise crosstalk effects the line and as I was the first to be connected to the fibre cabinet I could expect a lot but even then I've not seen people report a drop of around 40% in speeds like I've had (especially in under 2months), anyway since my line went down for the first time in ages today I decided to look at some of the other graphs (I was only really using it to track speed and noise margin before).

Below is a pick of the overall line stats for my line and wondered if anything stuck out??.

http://i206.photobucket.com/albums/bb242/Master_Yoda...

What I will say is when I look at the graphs over the time I've been getting the data I noticed that the following happened a lot.

http://i206.photobucket.com/albums/bb242/Master_Yoda...

If you look at the above pic (the 2 pics are an hour apart) the bits per carrier falls a lot in the 2nd pic from the first, and then the next hour it would go back to normal and then 6 or so hours later it would drop off big time again and wondered if this was normal?, and if anyone knew the reason it could be happening???.

I noticed later on that month that I wasn't on the latest firmware for the modem so updated it

http://i206.photobucket.com/albums/bb242/Master_Yoda...

from that pic it seems to have decided that the tones it was sharing for download/upload have now changed to download only but it no longer seems to be dropping off big time like it did before (or at least not in the hours it's taken it).

In that last pic it's noticeable very near the beginning in the lowest tones that the bits per carrier drops off a lot (from 12 to 4) and then shoots back upto 12 and then gradually falls away.
I had a look around to see if that was normal and someone else had something similar and people seemed to think that it was a "bridge tap" involved somewhere and wondered if this was the case with mine??? and if it is could that have been what was causing the issue when I was on ADSL and the line kept going down when the phone rang?.

Any info on any of the above would be appreciated.

thanks
Mike
Standard User Zarjaz
(knowledge is power) Tue 10-Jun-14 15:08:56
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Re: line issues???, possible bridge tap


[re: IranianGiraffe] [link to this post]
 
After that many engineer visits, you'd have hoped one of them would have picked up on a bridge tap. And TBF the Brandenberg test system is very astute at picking these up, so a simple test would have identified it.

Standard User IranianGiraffe
(regular) Tue 10-Jun-14 15:20:50
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Re: line issues???, possible bridge tap


[re: Zarjaz] [link to this post]
 
All I will say is that a lot of them didn't even look for a fix all they did was check to make sure the line was working in my house at the master socket (which it always was as it only ever went down when the phone rang) and then said there was nothing else they could do as they had no issues when they got there.


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Standard User 4M2
(knowledge is power) Tue 10-Jun-14 16:00:58
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Re: line issues???, possible bridge tap


[re: IranianGiraffe] [link to this post]
 
In reply to a post by IranianGiraffe:
All I will say is that a lot of them didn't even look for a fix all they did was check to make sure the line was working in my house at the master socket (which it always was as it only ever went down when the phone rang) and then said there was nothing else they could do as they had no issues when they got there.


I had that problem (6 rings and the router would drop sync due to a massive burst of errors leading to a downstream SNRM of 0dB ) a few years ago on G.992.1: eventually I got fed up with trying to get it fixed so switched to partial LLU (SMPF) G.992.5 and that cured the problem.

Whether that could affect vdsl (FTTC) in the same way I'm not sure but you will presumably still be using the same copper pair for broadband from the cabinet and for voice from the exchange?
Standard User Bald_Eagle1
(experienced) Thu 12-Jun-14 00:02:50
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Re: line issues???, possible bridge tap


[re: IranianGiraffe] [link to this post]
 
In reply to a post by IranianGiraffe:
I had a look around to see if that was normal and someone else had something similar and people seemed to think that it was a "bridge tap" involved somewhere and wondered if this was the case with mine??? and if it is could that have been what was causing the issue when I was on ADSL and the line kept going down when the phone rang?.



A bridged tap can usually be seen as a 'V' shape in the Hlog graph:-

example bridged tap


Your graphs don't show that & as Zarjaz mentioned, an engineer should normally spot one very quickly.


That connection went from a DS sync speed of 13.2 Mbps to 27.7 Mbps when the bridge tap was removed.

Edited by Bald_Eagle1 (Thu 12-Jun-14 00:06:56)

Standard User WWWombat
(fountain of knowledge) Thu 12-Jun-14 01:34:43
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Re: line issues???, possible bridge tap


[re: IranianGiraffe] [link to this post]
 
In reply to a post by IranianGiraffe:
What I will say is when I look at the graphs over the time I've been getting the data I noticed that the following happened a lot.

http://i206.photobucket.com/albums/bb242/Master_Yoda...

If you look at the above pic (the 2 pics are an hour apart) the bits per carrier falls a lot in the 2nd pic from the first,


I can say that my original line showed the same issue, back with an original modem and the original firmware. I never could figure out a pattern for when it gave the "low" version or the "high" version.

If you look more carefully, you can see that the effect only happens on tones up to 1000 (IIRC, but it could well have been up to 1024). Above that thresholds, the bit-loadings do not change.

However, the line speed doesn't actually change when the graph does, no re-sync occurs, and the uptime just keeps counting on.

I reached the conclusion that it was a bug in the way the Huawei output the bit-loading numbers sometimes.

I never had the issue once I moved house, on either old or new firmware - though I did get a new modem which may have been the cause of the fix.
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