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I'm a system administrator for a large seasonal resort. There are approximately 150 summer cottages there. All are currently served by a mix of ADSL and VDSL2 over twisted pair telcom feeder cables.

The longest runs are 3000 Ft or 914 meters.

The twisted pair cabling looks like this:

enter image description here

As you can see there is no "binder" or plastic coating separating pairs. They are just all mixed together.

We are considering replacing all the ADSL2 equipment with VDSL2 DSLAMs.

I'm very concerned that this could lead to major performance issues due to increased crosstalk between pairs. I know ADSL2 handles this better.

Is there any way I could better account for this risk? I don't want to buy $30,000 worth DSLAMs plus the labor cost of installation only to have the deployment fail.

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Dec 25 '18 at 9:20
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They are just all mixed together.

No, they're not. Each pair must be kept together at all times; if you separate or recombine the single wires crosstalk goes through the roof and all is lost.

Depending on how the trunk is actually deployed, crosstalk might be a non-issue. Vectoring is required when numerous links run in parallel for some distance - looking at the scenario neither the number nor the distance require vectoring.

Assuming that the pairs fan out fairly quickly in your scenario (after a few meters) I think crosstalk isn't such a big problem. However, since you terminate all lines in a single DSLAM, vectoring might just be a question of firmware version or licensing.

I'd ask the vendor about the scenario and whether it's possible to get a 30-day trial period.

And finally, if you work on the cabling in the future you should consider switching to fiber. Preterminated is pretty low cost, just don't fall for the usual OEM SFP ripoff.

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  • Thanks for the reply. The pairs remain twisted together but aren’t separates by any plastic — other than than that which wraps each I individual strand. There is also approx 2-3 feet of untwisted wire in each pedestal. They are spliced together with jelly/butt crimps. They do run parallel for long distances in the trunk. 2000ft to the last pedestal which services 50 cottages. What constitutes a “long distance” in this case? Fiber is our long term goal but would cost approximately 6 times to deploy. It seams as though copper is a better solution near term while they save for GPON.
    – Cggart
    Aug 23 '18 at 14:56
  • Additional plastic insulation between pairs doesn't make much of a difference. Vectoring is designed for reducing FEXT on large trunks with several hundreds or even thousands of participants - you're far away from that. Additionally, vectoring is a requirement when you need to offer several 100 Mbit/s in these large trunks. I'd do a trial to make sure, but chances are good it'll work right away. I'm also not sure if GPON pay o
    – Zac67
    Aug 23 '18 at 16:40
  • Thanks, that’s reassuring. We already have VDSL2 deployed for about 12 users — it is underperforming quite a bit but still providing good speeds within that range. One connection at 3000ft gets between 25-36Mps My concern is deploying at scale. Once all 150 costumers are using the trunk at the same time will cross-talk cause massive issues? I don’t know how to test for that short of actually buying the equipment and deploying it which would be a costly mistake if it didn’t work.
    – Cggart
    Aug 23 '18 at 16:47
  • (cont'd)... if GPON pays off for such a small installation. You can terminate 1000BASE-LX or -BX for as low as 70€ per port pair - once you've got the fiber deployed.
    – Zac67
    Aug 23 '18 at 16:48
  • If you're not planning to exceed 100 Mbit/s you won't need the FEXT reduction from vectoring. A reasonable vendor should allow you to test-drive the equipment for 5% or maybe 10% of the cost if you return it. Also, they should know what their products can do.
    – Zac67
    Aug 23 '18 at 16:50

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