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Author Topic: Near End Cross Talk  (Read 1011 times)

lofgents

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Near End Cross Talk
« on: December 24, 2017, 09:35:14 PM »

I am not in the UK and am responsible for the wiring of the incoming telephone line from the entrance to our property.

We are being affected by near end cross talk and experiencing 25% loss in service which I can prove by unplugging my neighbors modems.

The distance from our house to the ISP connection is around 80 metres would replacing the conventional cable with cat 5 or cat 6 help the situation.

I would be interested to hear if anyone has any experience in trying it, thanks for reading.
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burakkucat

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Re: Near End Cross Talk
« Reply #1 on: December 24, 2017, 10:01:55 PM »

The question has to be asked --

What sort of cabling is currently in use, both for your own circuit and for that of your neighbour(s)?
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lofgents

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Re: Near End Cross Talk
« Reply #2 on: December 25, 2017, 07:18:59 AM »

The telephone company use a multicore solid cable probably 26 swg to each property and then each owner has their own cable from the property entrance to the house, the 2 neighbors in question have about 10 metres of cable from the property entrance to the house.

We have a 4 core cable solid copper only using 2 of the cores again around 25 swg and about 80 metres from our entrance to the house.

When the furthest neighbor plugs his modem in my snr margin drops from 9.0 db to 7.5 db and when the nearest neighbor is connected it drops from 7.5 to 4.5.

These figures were recorded at 9.30am. If you need any more info please ask.

Thanks and Happy Xmas
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kitzuser87430

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Re: Near End Cross Talk
« Reply #3 on: December 25, 2017, 08:20:58 AM »

What technology is this ADSL or VDSL?

I would have thought that changing the 80m or do from the property entrances would not change anything unless these wires are in the same multicore cable.

What distance from the DSLAM or exchange are you?

Cross talk can only occur in multicore cables so it is more likely that the telephone companies wire is where the cross talk is occurring.

Ian

Merry Christmas
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lofgents

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Re: Near End Cross Talk
« Reply #4 on: December 25, 2017, 08:45:25 AM »

We are VDSL2 and line att is 26.5 db (from dsl stats) downstream rate is 35Mbs without neighbors connected dropping to 28Mbps when they connect their modems . I do not think the modem is reporting the line attenuation accurately because on a different screen the modem reports 21 db my estimation from Google maps is around 500m but this is guessing the route the cable follows.

Thanks and Happy Xmas to you

Dave
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burakkucat

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Re: Near End Cross Talk
« Reply #5 on: December 25, 2017, 05:00:59 PM »

Thank you for describing the current situation.

The coupling between your circuit and that of your two neighbours must be taking place within the common, multi-core cable. To replace each individual service feed with either Cat5e or Cat6 cable will not help. At best all you will gain is the knowledge that the wiring is new, with freshly made connections.

I presume your neighbours see a similar effect, with your modem being a source of NEXT to their circuits.

I wonder if the three circuits are using individual twisted-pairs within the multi-core cable or, possibly, there is one or more cases of split-legs.

If you have not already done so, could you and your neighbours contact the service provider and arrange for them to visit all three of you & to perform some tests?
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lofgents

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Re: Near End Cross Talk
« Reply #6 on: December 26, 2017, 06:04:38 AM »

Thank you for describing the current situation.

The coupling between your circuit and that of your two neighbours must be taking place within the common, multi-core cable. To replace each individual service feed with either Cat5e or Cat6 cable will not help. At best all you will gain is the knowledge that the wiring is new, with freshly made connections.

I presume your neighbours see a similar effect, with your modem being a source of NEXT to their circuits.

I wonder if the three circuits are using individual twisted-pairs within the multi-core cable or, possibly, there is one or more cases of split-legs.

If you have not already done so, could you and your neighbours contact the service provider and arrange for them to visit all three of you & to perform some tests?

Thank you for the reply I have been chasing the ISP since beginning of October had 2 engineers who said there is not a problem then managed to push it further and they say yhey have arranged for a contractor to come and do some re-wiring. The problem we experience is that the system (VDSL2) is fairly new to this area and the local techs are maybe playing catch up with the technology.

I was trying to make sure my own installation was as near 100% as it could be so they could not try and lay any cause to me.

Some of the background to this is that we are in a rural area and all our power and telephone cables are overhead and we have power outages during rain and windy periods these are very quick blips but since the new cabinet came on line we lose internet after one of these blips. I have U.P.S. on all my kit but the new cabinet has no battery back up so we have to wait till the modem re-establishes connection with the cabinet. While its doing that we get a large amount of FEC and CRC errors I don't know how badly this affects the DSLM as we rarely go 7 days without a power blip.

Thanks again for the explanation.
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jelv

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Re: Near End Cross Talk
« Reply #7 on: December 26, 2017, 10:06:47 AM »

Is there any chance of temporarily connecting the modem at the property entrance? If you then saw the same drop when the neighbours connect it would prove it is not your wiring.
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lofgents

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Re: Near End Cross Talk
« Reply #8 on: December 26, 2017, 10:18:37 AM »

Is there any chance of temporarily connecting the modem at the property entrance? If you then saw the same drop when the neighbours connect it would prove it is not your wiring.

Yes I have a long power extension and a spare socket so it would not be a big problem to try it I may just do that as we have a good weather forecast for a few days.

I did do this a while ago when we had adsl issues to prove it was not our cable run as the local tech was blaming this. It is an easy get out for them to say old copper or it is your cable etc. there is only one knowledgeable guy we have seen and he is difficult to get hold of.
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