What does the NBN look like?
The rollout of the NBN will represent a huge improvement in Australia’s online capacity whether or not it goes to the home or only to the node. A lot has been said about the network but what about the actual cable that is going to be bringing your downloads? We were lucky enough to have the anatomy of the NBN cable explained to us by Ross Finlay from Light Networking.
The particular cable was produced by Corning and is made up of a number of components that all have their own jobs. This is not like the cable connecting your DVD player to the TV.
The very outside of the cable is a green outer sheath (A). This hard nylon jacket provides light armouring to protect the cable, primarily against termite attack.
Within this sheath is a second black sheath made of polyethylene (B). This sheath fills in the low spots to make the cable cross-section circular and holds the components underneath together. The properties of polyethylene also result in this sheath adding a small amount of crush resistance to the cable.
The next layer is one of the most important protective elements of the cable but is often overlooked. A third sheath is made from woven fibre that swells in water (C). By swelling when wet this sheath stops water (and contamination) seeping down the length of the cable if the sheath is cut (e.g. rodents) which could affect the long term function of the cable.
Inside the sheaths you will find orange ‘rip cords’ on opposite sides of the cable (D). These rip cords make it easier to remove the sheaths when joining cables or when the cable has to be terminated.
To keep the cable as circular as possible ‘filler tubes’ are included. These filler tubes do not carry information of any kind but help give the cable structure and in doing so protect the other components on the cable from breaking and shearing (E).
Finally, the actual cable (F). Within all this protective structure there are four loose tubes, each coloured to make them easily identifiable, which each contain a stack of 12 ribbons. Each ribbon carries 12 fibres. This means we have 144 fibres per tube and therefore a grand total of 576 fibres in the cable.
In the very middle there is a final structural element made of fibreglass and epoxy resin which gives the cable additional strength and rigidity (G).
So what is this cable capable of? Well unlike copper wire cables like the one in cross-section here, the NBN cables are fibre optic and transmit a signal of light. The light shone down the fibre is made by a laser (or more accurately lasers). Each laser has a frequency of ~ 200THz or 200,000,000,000,000 cycles per second. As we are interested in the information load of the cable this is converted to ‘bits of information’ or 200 Terrabits per second.
This alone is a large amount of information but the real advantage to using light in an optic fibre is that, unlike copper carrying electrical signals, optic fibre can carry multiple different colours of laser light at the same time. In fact the NBN cable can accommodate 180 lasers at once, per fibre.
This means that if you take the frequency of the lasers (and in the industry they drop a zero from the frequency to be conservative, ie they work with a standard frequency of 20THz rather than the best case scenario 200THz), multiply that by the number of lasers that can be used at a single time, and multiply that by the number of fibres in the cable we can calculate the total amount of information the cable can carry:
20 Terrabits per second x 180 x 576 = 2,074 Petabits per second.
Standard information load of one fibre x number of lasers that can be used at a single point in time x number of fibres in a cable = Total information load of cable.
What does 2,074 Petabits per second actually mean? Well it’s equivalent to 32.4 million million phone calls. It means a huge capacity for carrying data!
Understanding numbers that high and abstract, is hard work. As a comparison, this cable will have roughly the same capacity to transmit information as Tasman 2, the cable laid between Australia and New Zealand in 1992. Put another way, the demand for fast and reliable internet, alongside the rapid advancements in technology, has meant that a decade after Tasman 2 was laid to provide state-of-the-art communications between two countries, the same information load can be sent to every home, or a node near every home.
This almost seems excessive until you really think what the world was like in 1992, compared to the world we live in today. The question is, will this still be enough 10 years from now?
By Francene Connor
Feature image “NBN Co fibre optic cable being laid in Tarcutta St in Wagga” sourced from Wikimedia Commons and authored by Bidgee.