I Hope I'm at the right place. I am trying to figure out why RJ45 jacks and plugs require 2 incoming wires and 2 outgoing wires to work. Why is just 1 incoming and 1 outgoing not enough? IS there a bandwidth limit on 24 gauge wire? I also just read this on Wikipedia " The cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet)". If cat 5 supports gigabit, then why is Google fiber such a big deal and why don't we already have gigabit nation wide in the US?

1 Answer 1


Continue reading. Ethernet uses a "balanced pair" for TX/RX. So there's a positive and a negative lead. 10/100 only needs two pairs (one TX and one RX); gigabit needs all four.

Fiber is far superior to copper in both noise immunity, and transmit distance. The maximum distance for twisted pair is 100m -- and all too often many network cards and cheap switches have insufficient power to drive the full length. Vs. multi-mode fiber going 500m, and single-mode fiber spans of 80+km. (120km is possible.) Plus, since photons don't interfere with each other, one can (and xPON does) use a single fiber.

"Gigabit Nation"™
The lack of a "gigabit nation" in the US is mostly a function of the market. There's very little monetary drive to build such networks. The copper phone line across the country can only get you so far -- and they aren't going anywhere trying to push ethernet ('tho there is a Long Reach Ethernet standard.)

AT&T's Uverse DSL network is a great example of how poorly thin copper wires are for high speed data -- a VRAD (fiber node) has to be within ~4k wire-ft of the customer and then they may still need two pairs. They aren't stringing fiber everywhere simply due to cost -- instead, continuing to milk all the copper they already have.

Verizon FiOS is an example of the opposite. They've spent billions running fiber. And where they ran fiber, they've been known to rip out the copper. Firstly, copper is a valuable metal. Lastly, they aren't required to share their fiber like they are copper (aka "open access".) That, btw, was the concession to get them to do this in the first place.

Google, Inc. has money to burn. (apparently) It's great advertising. And it does promote competition and innovation.

  • I don't think you could have answered it better, thanks I really appreciate it.
    – Cam Jones
    Dec 16, 2014 at 6:02

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