Dr John Cioffi on the Viability of 1 Terabit DSL Copper Line Broadband

4. In a real-world environment the traditional twisted pair copper lines, such as those that run between Openreach’s (BT) street cabinets and homes or offices in the UK, don’t always appear to be setup in a way that would necessarily favour a Terabit DSL style waveguide transmission.

In your view, how realistic is this likely to be as a solution for potentially connecting individual homes in such an environment?

ANSWER:

Yes, that is true and was true for all DSLs. Generally, solutions to these types of problems arise. ASSIA is often considered to be the world expert in diagnosing and fixing (often automatically with optimization software that tunes everything) these types of problems for all types of copper (and wireless) connections. These problems will get solved for any method.

5. By the sounds of it TDSL would need to employ some complex Vectoring in order to tackle crosstalk style interference at the stated speeds. The current generation of considerably slower G.fast connections are already struggling with this challenge over larger port counts (heat, power, cpu, space etc.) and it seems to follow that Terabit DSL might be an order of magnitude more difficult to resolve, is that the case?

ANSWER:

Those problems will magnify with TDSL, so you are correct. However, early forms of DSL were also deemed too expensive and today are dime-store cheap with ADSL chips using well below a watt in total power consumption and having sub $1 costs/port. They were once even more expensive and used more power than today’s G.fast chips. When there is volume purchase, then these costs will reduce.

The issue in the UK has been repeated calls for fiber all the way to the home. This is too expensive, and not affordable. Other copper (and wireless) solutions are really the only answer, but that gets twisted to mean that BT and the operators are not investing. They have been embarrassed into staying away from very copper technologies that could help the UK progress much more rapidly to high-speed connectivity because it looks like they’re not investing. Indeed, if they were allowed to invest in the copper technologies more, then it would be cheaper and faster to the higher speeds desired.

Firing executives at operators will not change the economics. When mass volumes are demanded for chips, power and cost will reduce rapidly.

6. Speaking hypothetically, in terms of potential deployment costs, what would be the key pros and cons of TDSL versus a G.fast style solution that in its cheapest form can be deployed from existing street cabinets?

ANSWER:

It’s too early to answer this question really because the precise characterization of the waveguide improvements needs more characterization first before a network-planning exercise can be undertaken.

7. We’ve heard talk about TDSL being able to deliver speeds of up to 10Gbps over 500 metres of copper cable, but how would it fair when travelling over much longer lines of up to around 2000 metres and what sort of adjustments might be required to make that work (if any)?

ANSWER:

That is what everyone asks, including BT in the UK. It turns out the longer distances complicate the waveguide flow (even at lower speeds attempted). There is some hope for symmetric 1 Gbps at 700m. That is as long as anyone has attempted to speculate so far in terms of length. There are some “lowest usable” frequency effects that start to dominate as the length gets beyond 700m.

8. Last year’s TDSL announcement sounded similar to the proposed AirGig solution from AT&T Labs in 2016 (here), which finally entered the trial phase at the end of 2017. What are the key differences between TDSL and AirGig and do you see the potential for any clashes over related technology / patents?

ANSWER:

Airgig uses power lines and one of the waveguide modes known as the surface wave. It is an early form of waveguide use (that was postulated over a century ago by Sommerfeld, Marconi, and others) with a single wire. There is no MIMO, but rather a highly directional single antenna (which is kind of like MIMO) spaced every few 10’s of meters or so to try to keep the energy from drifting too far from the power line.

AT&T’s attempts to explore in this area should be commended. They’ve had some interest in other waveguide methods suggested here, but probably need to put more effort into it as yet (after all they own the phone wires, but need to lease power lines from the electric company).

Airgig reportedly has had problems with moisture on the power lines, similar to the moisture problems that plague most of mm wave transmission trials today. The binder of wires does not have this problem presumably, but has its own other set of secondary effects that will need to be addressed as well. All are good ideas, but need time, effort, and of course money to be developed into field-hardened systems.

9. Finally, how serious are ASSIA about turning TDSL into an actual product that operators can use?

ANSWER:

We are software company, so do not make hardware. We’ve been willing to work with all to help it progress, and some have been interested in doing that. We cannot do it by ourselves.

End.

Thanks to Professor Cioffi for his detailed insights into TDSL and its potential future. We look forward to seeing how the proposed technology develops.