VDSL2 vectoring recreates telco monopoly

I love being on a fibre to the node connection. Before the FTTN cabinet was put in and I got VDSL2, the ADSL2+ broadband from the old phone exchange miles up the road spluttered along at six to seven megabit per second downloads, and a tenth of that up, on a good day.

When VDSL2 went live in April 2011, the connection speed jumped to around 30Mbps down and 8.5Mbps up. The more than ten-fold increase in upstream speed is hugely important, as I can deliver material ten times as fast, and the fast downstream isn’t to be spat at either.

It didn’t stop there though: to improve the signal in the house, the copper network operator put in a new, short length of shielded wiring, bypassing the existing cabling. That took most of the day for the installer, who had to crawl under the house for hours in uncomfortable heat.

My ISP knows a thing or two about VDSL2 and applied some of this nous. It organised a better router but also applied a wider spectrum profile and had interleaving removed on my clean line so that latency dropped to below 10ms locally.

The result? Fantastic: 67Mbps down, and 10Mbps up. Seriously, once you get quick broadband like that, you don’t want to go back to anything slower.

Except for one thing - I’m now down to 41Mbps downloads after a stint on just 30Mbps as a “dynamic line management” bot kicks in at seemingly random intervals and spots electrical problems on the connection.

According to the network operator, the drastic drop in speed is due to more ADSL2+ connections causing interference on the binder.

A binder or a sheath holds the pair of copper wiring going to your premises. Yours and the copper pairs for many other premises, that is.

I’m a bit dubious about the network operator’s explanation for reasons outside the scope of this piece, but there is no doubt that pushing high frequency signals through unshielded copper wire pairs will cause “cross talk” and interference.

This is just how such electric signals over copper behave. The copper network was not designed to transmit high-frequency signals and the more you do it, the chance of performance degradation and variation shoots up.

And with that comes customer unhappiness because an originally fast service drops by half or more of its original speed and the problem can’t be remedied. Or can it?

Read on to find out about the solution - and the potential consqeuences for the telco market...

Cancel that noise

Researchers and engineers have actually come up with a few tricks to minimise the effect of the interference. One was developed by John Papandriopoulos at the University of Melbourne, and involves balancing the spectrum used for the signal in DSL circuits, so as to arrange it either to provide the best throughput or maximum stability.

Spectrum balancing can be combined with noise cancelling, or vectoring and this is where it gets interesting.

Vectoring is held up as the silver bullet that will take care of all the problems with interference. It works in a similar fashion to newer multi-antennae MIMO techniques, and basically removes noise on the line.

It is extremely clever stuff, but how easy is it for operators to deploy it on the network?

It turns out that vectoring requires quite some change for VDSL2 deployments. First, vectoring uses modems at each end of the line to calculate and remove the line noise.

Obviously, the modems at both ends need to support vectoring – new customer premises equipment is needed, in other words – but they also need to talk to each other. Ideally, the modems should be made by the same telco equipment vendor for best interoperability.

So it follows that all the copper pairs in the binder also have to be controlled by one service provider, otherwise vectoring won’t be effective. That stands to reason as vectoring takes into account the interference generated by all the copper wires, so if some are left to their own devices, it’s just not going to work.

What that means is that there will be no more unbundled local loops if vectoring is to take place. A single service provider will manage all the copper, with wholesale access done at the bitstream level.

This is before you consider that vectoring doesn’t extend beyond 400 to 500 metres at the very most, necessitating a large number of cabinets (“nodes”), each with data backhaul and power requirements.

Solution to a problem of a bygone era

The above is of course a dream scenario for traditional telcos and their vendors: one network owner-operator with a single equipment supplier, set up with public funding.

From a competition point of view, however, a single service provider managing the vectored lines is suboptimal. Wholesaled bitstream access would mean lower margins for ISPs, and far less product differentiation. You basically get the vectored VDSL2 flavour that the service provider offers and that’s that.

For customers, less product and service differentiation spells limited choice. Just like how it used to be.

Monday will tell if the NBN Co review underway by the government will propose a return to the era of a monopoly infrastructure provider for the sake of politics.

Juha Saarinen is a technology journalist based in Auckland, New Zealand.