pins 1, 2, 3 and 6

Here is another obscure item but I think you’ll like it…

In practically every modern office building and indeed in many homes, you will find hundreds if not thousands of metres of network cabling. I’m referring to the cables, slightly thicker than telephone wires, that run through walls and ceilings, are stapled under carpets, and connect computers, printers and servers to hubs, switches, and routers. They are almost always blue although sometimes the shorter ones are grey. Look around McGill and you’ll spot them; the ceiling in the basement of Burnside is a good place to look.

These days most network cabling is ushielded twisted pair (UTP) – inside that blue or grey outer sheath are a series of small copper wires twisted together, each one wrapped in its own insulation. Well before the advent of computer networking, voice communication was already requiring huge quantities of UTP cable but the modern local area network (LAN) increased the demand for this kind of cabling exponentially. It would be difficult, maybe even impossible, to estimate the amount of UTP cabling in use today. Increasingly, organizations are switching to fibre optic cables for longer distances; these cables carry thousands of times more data than their copper counterparts. And the migration to voice-over-IP technology that essentially combines voice and data on one cable is also reducing the use of UTP cabling. But the resource use by cabling of all types cannot be ignored.

Imagine all the plastic and copper needed for all that cabling and imagine what will happen to it all when eventually fibre replaces all of it. But this post is not about the basic environmental consequences of network cabling, there’s a more interesting tidbit to share…

Those blue network cables are 4-pair, which means there are 4 pairs of wire, 8 conductors total, inside each cable. At the end of the cables are RJ-45 connectors, they sort of look like oversized phone connectors. But here’s something that most people don’t know: only half of the conductors in a 4-pair UTP cable are needed. Ethernet networks, even gigabit ethernet, only use 4 wires. According to official Ethernet cabling specifications, the other 4 wires are reserved for “future use.” Now imagine all that cabling all over the world, half of all the wires inside those cables are unused, completely wasted. You could create a perfectly functioning network cable with 2 pairs instead of 4. In fact, many of the cheaper cables you find at FutureShop or RadioShack are made this way.

Why did this happen, you might be thinking. Why would they come up with a standard that only uses half the capacity of the cable? Could it go faster if they used all the wires? All good questions and maybe ones I will answer in my paper…

Some links with cabling specs, you may have to scroll to find relevant info:
Cisco Documentation
Part of course outline at Del Mar College
Information from a cable vendor

2 Responses to “pins 1, 2, 3 and 6”

  1. sieber says:

    Fascinating. Your post reminds me of something I always found astounding in urban planning. There is a phenomenom called “feral cities”, which is a complete breakdown in the fabric of a community. This breakdown is so complete that the city is too dangerous for police; the rule of law is by gangs. In the US, you’ll see it in parts of Los Angeles and in East St. Louis. What I found amazing is the way in which people cannibalize houses: they strip the house of all its wiring. This is so much work for so little compensation (the market for copper is not good). Yet, in some places, the cost-benefit analysis works out.

  2. Jean-Sebastien says:

    I think it’s funny that they left half of the wires for the Future… and didn’t think that the Future might be
    wireless. It’s the way we seem to be going 🙂