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Standard User woodpeckerx
(newbie) Fri 22-Aug-14 16:53:16
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2x VDSL2 80/20 lines interfering


[link to this post]
 
Hi folks,

Had BTOR out all day trying to sort out a fibre problem, I have 2x VDSL 80/20 lines, one from Talktalk and one from BT. BT line uses a homehub5 as modem, TT uses their HG635 super router.

Each line works fine on its own but if both modems are on the speeds plummet.

The TT line syncs at 79987 and shows a max rate of 100M
The BT line syncs at 79987 and shows a mas rate of about 87.5M

I called BTOR out because with both modems on we were getting full 79987 from the TT line but only 57M from BT.

The BTOR engineer found a minor fault on the BT line so re-terminated the junctions, it cleared his fault but made the fibre speed worse!

Sync speeds are identical with only one modem on, but with both on now the TT is down to 56M and the BT 53M

BTOR is coming back Tuesday but don't know what to do, one suggestion was to install a separate drop wire from the pole which I don't mind.

Anyone got any suggestions on this? I presume it is a crosstalk problem, I don't know whether noise vectoring is in use yet or whether these modems have that ability, any suggestions welcome, I did think about buying a Bipac 8800NL as an experiment to try a different modem although the speed drop is similar when BTOR had their test kit on the other line.

TIA
Administrator MrSaffron
(staff) Fri 22-Aug-14 17:11:33
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Re: 2x VDSL2 80/20 lines interfering


[re: woodpeckerx] [link to this post]
 
No vectoring around yet. One presumes the drop wire to the home is twisted pair and not very very old untwisted.

Changing modems may help, but its an experiment to see, have two fttc lines here but are much slower (18-21 Meg) and no ill effects. So needs some feedback from others with near full speed lines.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User adslmax
(knowledge is power) Fri 22-Aug-14 17:18:37
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Re: 2x VDSL2 80/20 lines interfering


[re: MrSaffron] [link to this post]
 
I shall avoid 2 x FTTC then! Not worth to lose speed risky!


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Standard User worldofadsl
(knowledge is power) Fri 22-Aug-14 17:38:14
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Re: 2x VDSL2 80/20 lines interfering


[re: woodpeckerx] [link to this post]
 
What type of drop wire do you currently have? Are there two twisted pairs?
Standard User woodpeckerx
(newbie) Fri 22-Aug-14 17:46:31
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Re: 2x VDSL2 80/20 lines interfering


[re: worldofadsl] [link to this post]
 
The drop wire is circa 5 years old from memory, it has 2 pairs in it, I presume they are twisted pairs.

The BTOR eng hung the tester on a separate test drop wire dangling from the pole and the max rate drop was a lot better, circa 20M better, up from 55 to 75.
Standard User woodpeckerx
(newbie) Fri 22-Aug-14 17:48:34
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Re: 2x VDSL2 80/20 lines interfering


[re: MrSaffron] [link to this post]
 
Will order a modem to test.

Can't understand how we lost about 25M from the TT line though, all he did was re-terminate a couple of joints on the BT line
Standard User WWWombat
(fountain of knowledge) Fri 22-Aug-14 17:57:29
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Re: 2x VDSL2 80/20 lines interfering


[re: woodpeckerx] [link to this post]
 
If that joint fix lets more power through the BT line, you might see an improvement to the BT line but it would/could produce more crosstalk onto the TT line ... so reducing the speed.

Of course, if there has been a lot of errors or disconnections on the TT line in all this messing around, you might have also triggered DLM to intervene; while it is a single line, there is enough spare overhead (20Mbps) to absorb FEC/interleaving and stay full speed ... but perhaps with crosstalk from the second line present, that spare overhead has disappeared, and FEC/interleaving combines to give the reduced speed.
Standard User woodpeckerx
(newbie) Fri 22-Aug-14 18:24:36
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Re: 2x VDSL2 80/20 lines interfering


[re: WWWombat] [link to this post]
 
Both lines got worse, the BT line went from 57 sync, 69 max to 53 sync 56 max.

He spent the whole day on the job and everything got worse, even though he didn't touch the TT line.

He got the DLM removed from the BT line.

DLM doesn't seem to be on either line as both will sync on their own to 79987.

I've pulled the BT line out at the moment as I don't want the TT DLM to kick in, assuming they have one.
Standard User BatBoy
(legend) Fri 22-Aug-14 18:53:39
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Re: 2x VDSL2 80/20 lines interfering


[re: woodpeckerx] [link to this post]
 
DLM on FTTC is provided by Openreach, not the ISP. After a reset, DLM will not kick in until the next day, assuming no major instability is found.


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Standard User woodpeckerx
(newbie) Fri 22-Aug-14 19:06:04
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Re: 2x VDSL2 80/20 lines interfering


[re: BatBoy] [link to this post]
 
Thanks, what I don't want is the DLM to drop speed on the TT line, I've pulled the plug on the BT line for now, I'm going to get a new modem to try in the morning, do you recommend I leave the BT line disconnected?

My TT stats at the moment with the BT modem off are:-

Upstream line rate (kbit/s):
19999
Downstream line rate (kbit/s):
79987
Maximum upstream rate (kbit/s):
31056
Maximum downstream rate (kbit/s):
99260
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