Coaxial vs Ethernet cable - What's the Difference?

Figure 1.  Axis of a circle

So it’s a line that runs right through the middle of a circle. A cylinder also has symmetry, and so it also has an axis. Cylinders are important to this conversation because a cross-section of a wire is shaped like a cylinder. We attempt to show the axis of a cylinder in Figure 2.

Figure 2.  Axis of a cylinder

Other shapes and objects have symmetry also, so they also have an axis with respect to that symmetry. But because of the pressure building inside my bilaterally symmetrical brain, that’s all I’m going to say about symmetry.

So the axis of a cable is the imaginary line that runs down the center of the length of cable. Now, how do two conductors in the same cable share an axis? One of the conductors, called the center conductor, goes right down the axis of the cable. The other conductor, called the outer conductor or the shield, wraps around an insulating material called a dielectric, which spaces the shield an equal distance away from the center conductor. You can get an idea of this arrangement from Figure 3. In cross-section, you can think of the center conductor as a line, and the outer conductor as a circle, and they both share the same axis!

Figure 3.  Structure of a coaxial cable

Coaxial cable is used for data, video, and voice transmission. It’s primarily found in radio-frequency antenna installations, cable television, satellite antenna installations, and yes, even Ethernet. In fact, the original 10BASE5 Ethernet standard used coaxial cable as its primary medium. But coaxial cable is relatively bulky, so it is expensive to install. It is capable of delivering the same bandwidth as twisted-pair cable over the same distance, and because it is shielded it offers protection from electrical interference. But because the shield must be properly grounded, also adding to installation expense, the 10BASE-T Ethernet standard made the switch to twisted-pair cable in 1990. For your entertainment, a backwards-compatible network card from that period is shown in Figure 4.

 Figure 4.  Network interface card with both coaxial and twisted pair connectors

Ethernet Cable (Balanced Twisted Pair Cable) 

Balanced twisted pair cable is commonly referred to as “Ethernet cable” or “network cable.”  How is it different from coaxial cable? In just about every way except they both usually contain copper. There is nothing in a twisted pair cable that shares an axis with anything else. In fact, it is the cable’s complete lack of symmetry that gives it its most valuable property. It is made of four pairs of insulated conductors. The conductors of each pair are twisted around each other (Figures 5, 6).

Figure 5.  The four pairs of conductors in a balanced twisted pair cable

Figure 6.  Cross section of balanced twisted pair cable

Not only is each pair twisted, but each pair is twisted at a different rate (coils per inch). That way, conductors within the cable are rarely, if ever, oriented parallel to any other conductors inside the cable, or outside. This allows the conductors to avoid noise and signal loss due to electromagnetic interference (EMI).

More about this can be found in our Cable Academy blog, Why Are Wires Twisted Inside an Ethernet Cable?

Like most things that are important within a culture, twisted pair cable goes by many names. In addition to twisted pair cable it is called datacom cable, network cable, data center cable, enterprise cable and category cable, but most people just call it Ethernet cable.

Optical Fiber

So what about fiber optic cable?

Nope. There’s only one conductor in there. Two conductors need to share the same axis for it to be a coaxial cable. But you know what? It is an Ethernet cable! That’s right; coaxial cable, balanced twisted pair cable and optical fiber cable are all Ethernet cables.

Look at the construction of an optical fiber cable in Figure 7.  All of those components obviously share the same axis. So isn’t that coaxial cable, too?

Figure 7.  Structure of an optical fiber cable

Nope. There’s only one conductor in there. Two conductors need to share the same axis for it to be a coaxial cable. But you know what? It is an Ethernet cable! That’s right; coaxial cable, balanced twisted pair cable and optical fiber cable are all Ethernet cables.

Final Thoughts

So, if these different types of media are all used to transmit signals over Ethernet networks, why is it that only balanced twisted pair cable is called Ethernet cable? Because the vast majority of people have only ever used twisted pair cables to connect to a network.

As we said above, the 10BASE-T Ethernet standard made the switch to twisted-pair cable in 1990. That happens to be the same year that the first web browser was written at CERN, a research institution in Switzerland. The World Wide Web became available to mainstream users in 1994 with the release of the Mosaic browser, later called Netscape. Over the next two decades use of the Internet exploded to include users from all over the world with virtually unlimited content. Almost all of these users connected to their networks with twisted pair cable.

So why do I call twisted pair cable Ethernet cable? I think it’s because all of my friends do.