You can use a wide variety of cable types in networking. Probably the least expensive

and most common type is the Unshielded Twisted Pair or UTP. Unshielded means that

these cables have no extra shielding on the outside of each wire to protect against

electrical interference. A variant of UTP is the Shielded Twisted Pair, or STP, which has

an extra shielding to prevent the leakage of electrical noise from one wire to another.

And why are these cables called "twisted pairs?" When you strip open the insulation of

these cables, you'll see pairs of wires that are twisted. The tighter they are twisted, the

lesser the electrical interference between them. Also, the tighter they are twisted, the

higher the category of the cable. Twisted pair cables come in different categories. The

oldest type is CAT3, which was used in old analog phones. CAT3 cables have a maximum

speed of only 10 megabits per second and are unlikely to be used anywhere today. CAT4

cables are also unlikely to be seen today. They were used with the token ring standard

and had a maximum speed of only 16 megabits. CAT5 cables, used in Ethernet

environments typical in the '90s and early 2000s, are suitable for up to 100 megabits

over a maximum distance of 100 meters. However, CAT5 cables have now been

superseded by the more popular CAT5e version that can support up to gigabit speeds.

Most new cables today are CAT6 and can go up to one gigabit per second for 100 meters,

or 10 gigabits for 50 meters. Within a single rack of servers, you can have several CAT6

cables and connect everything over inexpensive cables with UTP because the distance is

only a few meters. Another type of cable is fiber optic. As the name suggests, these

cables use light instead of electricity, which is great for running much longer distances at

significantly higher speeds. Fiber optic is also more durable and secure than electrical,

making them the best choice for long distances such as the transatlantic submarine

cables between North America and Europe. Fiber optic cables are usually of two types:

single or multi-mode. Single-mode cables have several thin glass strands (in rare cases,

plastic) covered by protective insulation. As single-mode cables have thin 10 micron

strands, they support a narrow range of wavelengths and higher bandwidths - making

them ideal for submarine cabling across continents. Multi-mode cables are much cheaper

than single mode across shorter distances. The fibers in these cables are thicker, from

50 to 100 microns. Because of their thickness, they can run a wide frequency of light

over shorter distances - from a couple of thousand meters to a couple of miles. Coaxial,

often called coax, is a third type of cabling that comes in many varieties. RG-59 cables

connected rooftop aerial antennas to television sets - they did not carry much

bandwidth, weren't very long, and were relatively inexpensive. Today, RG-6 cables have

mostly replaced the RG-59 version and connect your satellite dish to your television and

support much higher bandwidth. RG-11 cables connect buildings across much longer

distances. They have a thick wire in the middle, which is the conductor, surrounded by

insulation, shielding, and external cabling. While RG-11 cables can go long distances

because of the thick wire, they don't bend very well. There are many other cable

standards, including RG-62, that are not widely used. Apart from using a coax cable from

a cable modem to a wireless router or television, you are not likely to run into much

coax.

UTP Cables

Figure. Example of a UTP cable.

Unshielded twisted pair cables (UTP cables) are created when pairs of wires are twisted around each other to protect and cancel out interference from each other and outside sources. UTP cables were invented by Alexander Graham Bell in 1881 for phones and are still used today. UTP cables are widely used as analog phone cables and in copper Ethernet cables.

UTP cables come in six different standard types as defined by TIA/EIA 568. You can identify the type of cable you have by looking at the writing on the cable itself.

1. Cat3 supports up to 10 Mbps (Megabits per second) for up to 100 meters and is commonly used for phone lines today.

2. Cat4 supports 16 Mbps for up to 100 meters and is not commonly used today.

3. Cat5 is used in Ethernet LANs containing two twisted pairs allowing for up to 100 Mbps up to 100 meters between the device and the switch, hub, or router. This has been practically replaced by the Cat5e specification.

4. Cat5e doubles the number of twisted pairs to four for up to 1 Gbps (Gigabits per second) over up to 100 meters.

5. Cat6 is also used in Ethernet LANs and data centers. Cat6 is made up of four tightly woven twisted pairs (more twists per linear foot) and supports 1 Gbps for up to 100 meters or 10 Gbps for up to 55 meters.

6. Cat6a is an improvement of the Cat6 standard, supporting the same standards and lengths (with the ability to run 10 Gbps over 100 meters maximum), but using a higher quality cable that is more resistant to interference. This is most commonly used in wired networks today.

There are several different connectors that can be connected to the end of these UTP cables; the two most common are:

• RJ11: A connector that supports two pairs of wires (four total); typically used in telephones.

• RJ45: This is an end connector typically used with Ethernet cables and supports four pairs (eight wires).

Coaxial Cables

Figure. Example of a coaxial cable

Coaxial cables are analog cables made of copper but specifically engineered with a metal shield intended to block signal interference. This cable was patented in 1880 by Oliver Heaviside and was used as an improvement over the bare copper cables widely used in that day. The protection on the coaxial cable allows them to be laid next to metal gutters or other objects without receiving interference. Today, coaxial cables are mostly used by cable TV companies to connect their customers to the company’s facilities.

There are several types of these coaxial cables, but since they are not widely used in networking today, they are not discussed further.

Fiber Cables

Figure. Example of a fiber-optic cable

Fiber cables, or fiber-optic cables, use glass or plastic threads within cables to transfer the data using light (lasers or LEDs) as opposed to traditional metal cables using electricity. Fiber cables are useful for high bandwidth needs, meaning they can carry more data at one time. Additionally, they transfer data digitally instead of needing to convert data between binary and analog and back using metal cables. Since computer data output is digital, this transfers data in the computer’s natural way. Fiber cables allow virtually no interference to corrupt the data and are more reliable.

Fiber cables are lighter and thinner to install but are much more expensive. However, the technology community is continually trading out old wiring for fiber cables for the advantages listed above.

There are two types of fiber cables: single-mode and multimode.

1. Single-mode cables are made up of one single glass or plastic fiber. The benefit of a single fiber cable is the ability to carry higher bandwidth for 50 times the distance of a multimode cable. This requires higher cost electronics to create the light and thus is typically used for longer distances (hundreds or thousands of kilometers) and higher bandwidth applications.

2. Multimode cables are wider in diameter due to light modes being sent across the cable. Multimode fibers are highly effective over medium distances (500 meters or less at higher speeds) and are generally used within a LAN. They are also less expensive than single-mode fiber due to the potential for use with LEDs and other lower-cost options for creating the light.

The primary connector types used today are as follows:

• ST: This stands for a straight tip connector. This was the most commonly used connector with multimode fiber until the mid-2000s. It was used on campuses, corporate networks, and for military purposes. Today, LC connectors are usually used instead, as they are denser and more convenient at almost the same cost.

• LC: This stands for lucent connector. This is a smaller version of the standard connector (SC). This supports more ports to be used in the same space. This is probably the most common type used in corporate data centers today and is usually used with SFP (small form-factor pluggable) transceivers.

When choosing which type of cable to implement, the question of distance comes into play. If a customer is looking for great speed with distances over 100 meters, fiber cables are the right choice. What type of terrain will the wiring be subject to? Fiber cables are more protected from outdoor weather than traditional copper cables.

Additional Cables

Figure. Example of a crossover cable. It looks similar to a UTP cable.

Crossover: Crossover cables are used to connect two computing devices of the same type directly to each other. In computers, this is accomplished via their network interface controllers (NIC) or switches. With a crossover cable, the transmit connector on one end of the wire is connected to the receive connector on the other. These cables are used much less today, as many standards have the built-in capability to try straight through and then crossover if communication does not take place.

Patch: Patch cables are used to connect a device to a wall outlet, for example. The wall outlet is wired to another patch panel in the networking closet, and that networking panel is wired into a switch. These cables can also be used to wire servers in a rack to the top-of-rack (ToR) switch. Patch cables look similar to crossover and UTP cables.