Network Mediums

Typical communication between devices can travel several different ways and along different physical mediums. There currently exist three primary mediums for which data transmissions occur: wired connections, wireless connections, and fiber optic connections. Each of these mediums is used to move the data intact from point A to point B . The difference between the mediums lies in the way in which each of these mediums moves the data.

Wired Connections

The most traditional medium is one where copper wires physically connect two devices to allow communication. Its most popular form, which is often incorrectly labeled as an "ethernet cable", is twisted pair cable. A twisted pair cable contains several pairs of wires. When used for ethernet, this type of cable contains 4 pairs of wires, though only 2 of those pairs are actually used (except for gigabit ethernet, which uses all 4 pairs).

Fig. 2: Twisted Pair Cable

These copper wires are crimped into a plastic RJ-45 connector. An RJ-45 connector is very similar to a telephone wire connector,but larger. Category-5 (Cat5) wire is typically used to make a cable used for ethernet. Cat5 wire contains four twisted pairs of copper wires. It also comes in a shielded version that provides a small amount of shielding to help prevent signal interference. Twisted pair does have its limitations. It is more somewhat susceptible to interference and therefore can only run a maximum of 100m or 320 ft before signal loss occurs.

Another form of wired connection is coaxial cable. Coaxial cabling (see Fig. 1) has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

Fig. 1: Coaxial Cable

While coax provides good insulation and durability, its installation and connection methods can prove difficult. This wire is best suited for long, one way connections between devices. Coax cable is less susceptible to interference than twisted pair cable. High quality coax cable supports a maximum length of 500m before signal loss is experienced.

Wireless Connections

Wireless communications tend to use RF (radio frequency) to broadcast a signal. With the advent of wireless computer communication and the IEEE (Institute of Electrical and Electronics Engineers) 802.11 group of standards, networking computers has become even easier.  The 802.11 standard specifies an over-the-air interface between a wireless client and a base station, or between two wireless clients. This method of communication is often referred to as Wi-Fi.

Fig. 3: The Wi-Fi and Bluetooth logos

There are several specifications in the 802.11 family:

• 802.11 -- applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band
• 802.11a -- an extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5GHz band. This is the standard currently being used by NC State wireless access in classrooms.
• 802.11b (also referred to as Wi-Fi) -- an extension to 802.11 that applies to wireless LANS and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band.
• 802.11g -- applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band. This is the standard currently being used by NC State wireless access as a whole.

While the 802.11 standard is the most prevalent form of wireless communication used to network computers, there are other wireless methods that can be used to establish networks.

Bluetooth technology allows for short ranged wireless networks to be established. Bluetooth is used most often to establish networks between devices and a computer or a similar control device. Bluetooth keyboards, mice, and joysticks are some common peripherals. In addition, many newer cell phones and PDA's use Bluetooth to allow the use of handsfree devices or to sync with a computer without using a cable. Most Bluetooth devices have a range of 10m, but the technology does allow for ranges up to 100m. Bluetooth operates in the 2.45 GHz band. Bluetooth 2.0 allows transmissions speeds up to 2.1 Mbit/s.

Fiber Optic Connections

A much faster communication medium is a fiber optical connection. Fiber optic cables use pulses of light that can travel very fast (up to the speed of light) for great distances inside small strands of translucent fibers. Those translucent fibers are what make up the core of the cable. These plastic or glass fibers are surrounded by a plastic coating to help cushion the fibers. Surrounding this are kevlar fibers that are used to strengthen the cable and prevent breakage. Finally, an outer Teflon or PVC coating is used to wrap it all up.

Fig. 4: Fiber Optic Cable

Not only does the structure of the cable make for solid performance, but because the data is carried via light pulses, fiber optic cabling is not susceptible to electronic interference like traditional copper wired connections. Fiber optic cables can run 2000m without signal loss. With a cost on par with copper cabling, the fiber optic cable is the primary choice for today's telecommunication industry.