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Apr 7, 2009

National Broadband Network, Part 1

FTTN? FTTH? WTF? The NBN explained.

To get your head around the National Broadband Network, there’s three things to understand — and you can do that without too much technical knowledge:

  1. Speed
  2. Distribution technology
  3. Industry structure

Speed is all about bits and bytes, and how many of them you can transmit per second.

A bit is the basic unit of digital data, a zero (0) or a one (1). String eight of them together and you’ve got a byte, which can represent a number between 0 and 255. Or, suitably encoded, a letter of the alphabet. Use three bytes to represent a single dot (“pixel”) in a colour photograph, one each for the values of red, blue and green. So a photograph isn’t worth a thousand words, but something more like a million. Then if you want your picture to move, you need to transmit 25 frames a second — 25 pictures, that is.

While there are some clever compression technologies out there, the basic fact remains — if you want to stream high-quality video over the internet, you need to be able to send millions of bits of data every second. And so the basic measure of the speed of your internet connection is bits per second (b/s) or, more usually, thousands of bits (kilobits) per second (kb/s) or millions of bits (megabits) per second (Mb/s).

In the days of dial-up internet, the maximum speed was 56kb/s. Barely enough for audio at AM-radio quality. A technology called DSL uses higher-frequency signals, but still over the same copper wire as your phone used. A clever splitter box kept the DSL screeches separate from your voice, so you could both talk on the phone and use the internet at the same time.

Most DSL was sold as ADSL. The A stands for “asymmetric”, meaning the link is faster on downloads (data received by you), than uploads (data sent by you). Since most people want to receive web pages and online video rather than produce it, that’s fine. ADSL provides download speeds ranging from 128kb/s to 1.5Mb/s. At the top end, that’s just enough to watch the not-quite-TV quality video streamed from the likes of the ABC’s iView.

ADSL2+ is an improved version of that, with speeds up to 12Mb/s or even 24Mb/sec, depending how far you are from the exchange. This makes it possible to receive HD TV, or have multiple streams of data for everyone in your home.

There’s also “cable” internet, using the same coaxial cable as Pay TV. That typically runs 8 to 10Mb/sec. ADSL2+ and cable are currently the main systems for fixed broadband.

Going beyond these speeds requires new cables to be laid, either multiple air of copper wire or, more future-proof, optical fibre cables. Optical fibre is basically a thread of glass, and instead of an electrical signal the data is encoded on a laser beam. Fibre has the advantage that you can increase the data speeds by “multiplexing” — that is, using multiple frequencies of laser light to send many signals down the same fibre.

Fibre has the potential to eventually send not hundreds of Megabits of data per second, but thousands or perhaps even millions.

The question is then of where you lay the cable and that’s a question of FTTX. You use the optical fibre for the high-speed links between towns and cities. If you take the fibre to roadside boxes, and then use DSL or some copper-based cabling for the last few hundred metres to the home, that’s Fibre-to-the-Node (FTTN) or, of it’s a closely-populated area, Fibre-to-the-Curb (FTTC) or Fibre-to-the-Kerb (FTTK). The original NBN plan was FTTN, so that high-speed fibre would be shared with the others in your street.

If you take the fibre right up to the property, that’s Fibre-to-the-Building (FTTB) or Fibre-to-the-Premises (FTTP). If you take it all the way into the individual homes and apartments, that’s Fibre-to-the-Home (FTTH). The newly-announced NBN is FTTH, and while that’s a little more expensive up front, it’s the one with the greatest room for expansion in the future.

Crikey welcomes your dumb questions, and will find someone smart to answer them. Send your suggestions to with “clarifier” in the subject field.

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