Writings on technology and society from Wellington, New Zealand

Sunday, July 1, 2007

Submarine cables – our world is wrapped in fibre

Ever wondered how the Internet and telephone calls make their way across the oceans and around the planet? The whole world is girdled in optic fibre. Without it, we wouldn’t have the Internet, and international phone calls would all have that satellite lag.

On the 6th of June 2007, in my regular technology slot on Radio New Zealand National’s Nine to Noon programme, I talked about the history of the cables, how they work and which cables are in use around new Zealand today. Here are the notes of my comments, although I may not have stuck to them on air! At the end of the post are some links for further reading.

Q: Submarine cables – these are wires running under the sea?

A: Yes. There have been wires under the seas since the days of the telegraph. The first transatlantic cable went in in the 1850s, although it didn’t really work. But more followed very quickly. The first ones were laid by a man named JJ Thompson, a physicist in the fine tradition of the Victorian amateur – he was created Lord Kelvin by the queen, although whether his elevation was due to his physics work or the huge wealth he made laying cables, I don’t know.

Q: So these were telegraph wires?

A: The telegraph, like you see in old westerns. It sends pulses – on or off, Morse code. You need an operator at each end. The sender has a morse key – looks a bit like a stapler – that they tap up and down to form the dots and dashes of morse code. At the far end the operator listens, or watches the movement of a pointer, and writes down the pattern of dots and dashes. To send messages on a journey involving more than one cable, they had to be transcribed and sent separately across each.

Q: It sounds unbelievably slow.

A: And it was by our standards, but for the Victorians it was an amazing beakthrough. Before then, messages had to carried on horseback and by ship to the far flung corners of empire – it took literally weeks. The telegraph could get messages there in hours. This was extremely important, not just to the military, but to the big British firms operating transnationally and shipping goods all round the globe.

New Zealand got its first Cook Strait cable in 1865, and its first international cable was laid by the government in 1876 from Sydney to Cable Bay in Nelson. (The South Island had the bigger population and greater wealth at the time.) Even though it was hugely expensive to use, it was over capacity pretty much from day one and another cable was laid a few years later. The Cable Bay telegraph station had a crew of 25 men to keep it running. That station ran until the First World War when the end was moved to Wellington.

Q: So how expensive was the cable to use?

A: Fifteen shillings a word from New Zealand to the UK. That’s a dollar fifty per word, without allowing for inflation. Realistically that’s got to be tens of dollars per word in today’s money. But people paid this – governments used it, export businesses, and news wires of course – that’s why we still call them news wires.

Q: so what were these cables made of?

A: Copper wire, wrapped in layer after layer of armour and waterproofing. Modern ones are made of glass – optic fibres, but they are still wrapped in armour.

Q: these are the cables that carry phone calls and Internet today?

A: yes. People lay more and more of these fibre optic cables and their capacity keeps increasing – and we keep using more of it – blame the Internet for that.
But for a long time phone calls were carried by satellite. Satellite circuits have an annoying lag. You know, you have to wait for quite a while after someone’s stopped talking or you just end up talking across each other. We only really got rid of satellite voice circuits over the last decade or so – and you often still see them on live TV – let’s cross to our correspondent in London, and then we have to wait for ages for them to hear the question the interviewer in New Zealand asks and start to answer it.

Q: Why do you get that delay?

A: The signals are fast – they travel at a good fraction of the speed of light, which is enormously fast – but putting the signals up and down to a couple of satellites adds a great deal of distance to the path they travel through. That’s what adds the delay when you use satellites.

Optic fibres work by carrying beams of light. You put a laser at one end, and you get pretty much all the light out the other end that you put in, even though the fibre might be bent into curves. The light doesn’t escape from the sides of the fibre because it only ever makes a very gentle angle with the edge of the fibre as the fibre curves, and it gets reflected back into the fibre. It’s a phenomenon that scientists call total internal reflection. Of course, you have to keep the optic fibres only gently curved with no kinks for this to work, and they are bundled together in some stiff armour to make sure this doesn’t happen.

Q: So do these light beams go all the way along a fibre that thousands of kilometres long?

A: Pretty much. Sometimes there have to be amplifiers built into the cable every few thousand k’s. Those are a problem, though, because they wind up at the bottom of the ocean and are difficult to fix if they break, so the companies try to do without them.
You send signals down optic fibre by switching the laser off and very rapidly, in the modern equivalent of morse code. At the far end of the fibre you have a detector which converts light pulses into electrical ones. You can switch that light on and off very rapidly indeed – much faster than you could with electrical pulses, but the thing that makes light head and shoulders better than wire is that is has different colours, corresponding to different wavelengths of light. You can point a blue laser, a red laser and a green one down the same fibre, and have a red detector, a blue detector and a green one at the other end and you have tripled the capacity of the fibre. In practice you can use a lot more colours and some other clever tricks to allow you to get even more capacity from a single fibre.

Q: So how do you go about putting the cables under the sea?

A: First you start with a billion or so dollars depending on how far you need to go. Then you rent time on one of the cabling ships. These ships are special purpose vessels which reel the cable off the back as they steam across the ocean. If you are cable laying in shallow water, you should do what they call “plough burying” the cable, the ship tows a plough along the seabed and the cable gets laid in a trench and covered over. That’s to help guard against boat anchors breaking the cable. You need a team to be able to splice or join the cable – that’s a specialist job, you can’t just tape optic fibres together like you can get away with on wires. And you need the services of a repair ship when the inevitable breakage happens. That ship has to fish up both ends and splice new length in.

Q: So what cables are there in New Zealand today?

A: There are the Cook Strait ones of course – Transpower has two power cables and they both have data cables with them. It’s actually against the law to go trawler fishing anywhere near those cables, and the authorities use satellite to check that fishing vessels stay away. And Telecom and Telstra both have Cook Strait cables of their own which have gone in in the last 10 years. Apart from that, the main cable we rely on is called Southern Cross. That was laid in 2000, and is still seen as pretty modern. Telecom owns 50% of Southern Cross, and it looks like it’s been a pretty good investment for them. It paid for itself in the first year. Southern Cross is in the middle of an upgrade to about 1.2 Terabits per second capacity – that sounds like an unbelievable number until you realise that it only means the contents of a modern PC’s hard drive every second for the whole cable.

Q: Are there risks in being so reliant on the one cable?

A: The Southern Cross is really a ring of cables rather than just one cable. It forms a ring passing through Auckland, Sydney, California, Hawaii and back to Auckland. There are two separate cable landings in Auckland – Muriwai beach on the west coast and Albany on the east. If the cable gets cut anywhere signals are supposed to simply go the other way through the ring. That said, they did have problem in the early days when a ship anchor damaged the cable in Sydney harbour when another part of the cable was down for maintenance. Even so, it’s pretty reliable.

But there is a commercial risk in just having one cable. What if the owners decide to price it too highly – that would all of our Internet charges more expensive. Or what if they decide to prioritise traffic from Sydney to California ahead of ours? Telstra has announced that its beefing up its cables from Australia, and that will provide some competition. But some people are arguing that this is national infrastructure like roads and the government ought to provide it, as it did in the early days. Having excellent connections back to the rest of the world is crucial to New Zealand if we want to be less reliant on primary produce like we keep saying we do. Wellington entrepreneur Rod Drury wrote a piece on that which I’ve linked in the resources for today.


An entertaining Wired magazine article about submarine cables.

A history of Nelson’s Cable Bay telegraphy station.

The Southern Cross cable that links New Zealand to the world.

Wellington entreprenuer Rod Drury on why the government should fund another cable.

posted by colin at 3:56 pm  


  1. thanks for the help

    Comment by vinod — 10 July 2007 @ 8:57 am

  2. […] us courtesy of undersea cables that circle the Pacific. See Colin Jackson’s post and links: Submarine cables — our world is wrapped in fibre: …the main cable we rely on is called Southern Cross. … really a ring of cables […]

    Pingback by Groupings / South Pacific: wired for Internet — 6 September 2007 @ 11:05 am

  3. […] …is the title of an old book by Harry Harrison which I haven’t read, but I’ve always loved the title. The title captures some of the enthusiasm around connecting our world. And today, we connect our world with undersea fibre cables, as I have written about before. […]

    Pingback by » A transatlantic tunnel, hurrah! — 15 January 2008 @ 7:49 am

  4. […] article about the cable getting cut in the Middle East, and a link back to my previous programme on […]

    Pingback by » Foo Camp — 7 February 2008 @ 10:59 am

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