A few questions then about thicker cable:
1. Do Openreach have a choice of cross-sectional area cables to pick from for long lengths?
Yes. IIRC, the main options are 0.5mm, 0.6mm, 0.9mm.
2. What's the effect at very high frequencies? ( Is it simply the case that skin effect dominates so it's all about the circumference of the conductor? )
Good question, but no idea.
If you google this, "Cable reference models for simulating metallic access networks etsi", you'll find an ETSI document describing cable models for VDSL frequencies, and the parameters that apply to a variety of European cable types, including a few BT drop wires, and 0.5mm d-side cable.
There are similar documents describing more complex models for G.fast frequencies, but you need to be good at figuring out what to search for in ITU work groups; not everything is public - and BT docs are harder to find than some.
One of the leading g.fast researchers has a page here, with some documents from a Dutch perspective:
http://www.joepeesoft.com/Public/DSL_Corner/_Index.htmlhtmlThe section on " Modeling Copper Cable" has a good set of documents.
In fact, that ETSI document is on that page too.
Screening and crosstalk:
3. Is there a choice of screening types? geometries?
4. Number of pairs per bundle?
I think there is a possibility of screened cable, but it isn't commonly used. Most likely one screen around the entire bundle.
E-side can number 1000+ pairs, up to 4,800. As a guide, look at the two PDFs at the top of this page
http://www.btcables.com/products/voice/outside-plant-primary-cableD-side more likely to be 100 pairs. As a guide, look at the two pdf's at the top of this page:
http://www.btcables.com/products/voice/outside-plant-secondary-cableI'd like to understand a bit about what physical choices may become available to Openreach in the future.
If this myth about 10 Mbps USO has any substance at all in it, I wonder if in five years Openreach might plan some simple cable replacements / upgrades.
I've certainly seen signs that BT will alter copper wiring within bduk, so it is certainly possible this could happen. I do wonder whether they'd prefer to solve the problem through deeper fibre instead of upgraded copper. After all, by then, BT will be 3 years into their 10-year plan.
My observation is that a 10Mbps minimum is a technology killer ... It requires all 20CN, ADSL-only exchanges to be upgraded, either to 21CN, or to fully-fibred capability. At least it means that where BT will be part of the USO.
I agree with benji that wireless is better in some places. But that might turn out to be 4G with BT/EE by 2020.
