Shielded Twisted Pair and Fiber Optic Cabling

By Dan DiNicolo, September 4th, 2005 Posted in CCNA Study Guide Chapter 02. Subscribe to our RSS Feed

Shielded Twisted Pair (STP) cabling is very similar to UTP, with one key difference. STP incorporates an additional conductive foil shielding around each pair of wires. While this helps further cut down on EMI, STP is more expensive and can also be thicker and harder to install than UTP cables. STP cabling is most often used on Token Ring networks.

Fiber optic cabling is another option for network media, though considerably more expensive. This is not only in terms of the cost of fiber optic cables, but also related components such as network cards and switching equipment. Unlike UTP and STP, which run over copper wires, fiber optic cabling instead sends pulses of light through a pure glass core encased within Kevlar sheathing. The fact that light isn’t susceptible to EMI provides great advantages, especially in places with a high degree of possible interference such as factories or warehouses. Fiber optic cabling also allows data to be transmitted along much greater distances that traditional copper wire, in some cases up to hundreds of kilometers. Using fiber does have some disadvantages outside just cost - it’s significantly more difficult to install, and subject to various bending limitations. It is worth noting that fiber cables will have two separately encased fiber stands, one used for transmitting and the other used for receiving. In other words, the strand connected to the transmit port on one device will be connected to the receive port on the other device.

Different types of connectors can be used to connect to fiber optic ports. The most common are round plug-style ST connectors and square block-style SC connectors. It’s important that you make sure that you’ve purchased the correct cables to match the ports on your particular equipment.

The two main types of fiber cabling used on networks are single mode and multimode. Single mode fiber can span much greater distances and carries a single ray of light up to a number of kilometers. There are a number of factors involved in the distances that fiber optic cabling can span, though it mainly relates the micron diameter of the glass core. To be clear, a micron is one millionth of a meter. The most common diameter for fiber optic cabling is 62.5 microns. As the diameter on the cable decreases, the distance that can be spanned increases. Single mode fiber is most commonly used on networks that employ long-wavelength optics (LX).

Multimode fiber can also be used in long-wavelength optics, but is more commonly used with short-wavelength (SX) technologies. Multimode fiber carries many different light signals at once, each at different angles of refraction. It can only travel shorter distances, up to approximately 550 meters.

Fiber optic cabling is becoming popular on LANs, especially for use with Gigabit Ethernet. While fiber optic connections to the desktop aren’t common, you’ll often see them used for backbone or trunk connections between switches, and frequently for connections to servers as well.

Written by Dan DiNicolo - Visit Website

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