Cables beam future to our computers

Many of us will benefit in some way from the introduction of fibre-optic cables. Photo / APN

Copper is dead. Long live fibre. The rewiring of New Zealand for data communication began about 20 years ago with some forward-thinking people laying newfangled wires called fibre-optic cable. In those days the cables carried just a single strand of glass. Today they can have as many as 624 strands of glass fibre and each year manufacturers bring out cables with a bunch more.

Unlike the electromagnetic signals that pass along our copper telephone wires, these fine glass filaments transmit on beams of light. More amazing is the phenomenal increase in capacity (bandwidth) of these fibres. It's estimated that two strands of glass, sending and receiving, could carry the entire data, voice and video capacity of all of New Zealand.

These very large capacities, travelling on laser beams of light, give real meaning to the term "broadband". In contrast, copper phone wires have limited bandwidth, and although new technology has expanded what can travel down copper wires, it's dismal compared to fibre.

Fibre links easily offer 1000 times more bandwidth than copper, plus fibres can send and receive over distances 100 times further.

Fibre-optic cable itself is quite cheap - starting at $1.30 per metre for a cable with 12 strands and $2.40 a metre for "36-core" cable.

The expense is in putting it in the ground - although if you know how to use a mole plough you can lay the stuff like irrigation pipe for about $5 a metre.

Compare that with $30-$40 a metre estimates for laying fibre along footpaths in our cities, and fibre to the farm begins to look less difficult than it sounds. In the cities there are many ways to reduce costs - such as slinging fibre on power poles, sending it along existing waste and stormwater pipes and using low cost "micro-trenching" techniques.

Wholesale fibre is sold in several ways. Sometimes internet providers will buy "dark fibre" - a strand or two they then "light" themselves.

The problem with selling this way is that sooner or later all the strands will be sold off. Which is why bandwidth is mostly sold in chunks or circuits of various capacities. Network Tasman, for example, sells 1 gigabit-a-second circuits to businesses and internet providers for $1500 per month.

How do they do that? By clever technology that slices and dices colours, or wavelengths, of laser light into channels to carry different signals. It's common for cable operators to have equipment providing 256 channels each carrying 40 gigabits per second. Do the maths and that adds up to 10 tera (trillion) bits per second over a single fibre pair. Multiply that by multiple strands and you end up with quite a lot of circuits and quite a lot of capacity.

For cable operators, the excess capacity - bandwidth that expands in much the same way that computers keep getting faster and faster - is how they stay ahead of demand.

For consumers it means connections to their home delivering unheard of capacity in the blink of an eye. Today 100 megabits per second for $100 per month - tomorrow a gigabit and beyond.