Networking Media

Guided Media (Cables)

Cables are the guided media of communication, as they carry the data or voice in the electronic form from one end to another. Communication can be with the help of wires (cables) or can be wireless. In this section we will study about the cables as a means of communication. In the next section we will have a brief idea on the wireless means of communication. Most common types of cables are twisted pair, coaxial and fiber optic. So let's look at the advantages and disadvantages of each of them.

?  Twisted Pair

Twisted pair is the most common and ordinary cables. It is the wire which connects many businesses to the telephone companies. Twisted pair is insulated pairs of wires which can be packed quite close together. To reduce crosstalk electromagnetic induction between pairs of wires, two insulated cooper wires are twisted around each other. Each connection of the twisted pair requires both the wires. Tighter the twist better the support plus more the cost. Twisted pair can be installed in two or more pairs but they are in the same cable. Twisted pair is of two types Unshielded Twisted-Pair (UTP) and Shielded Twisted-Pair (STP).

Unshielded Twisted-Pair (UTP)

The common example of the UTP is telephone wire. The cable typically combines four pairs of wires inside the same outer jacket. Again the twist per inch differs among the pairs. UTP is divided into various categories depending on their uses for transmission. Some of them only support voice transmission while others support only data. Again they transmit at different speeds. Following is the table of categories of UTP.

As we can see from the table that all the categories differ from each other either due to the speed of transmission or by the contents of transmission. Today Category 5 is the most popular as it more convenient in increasing transmission technology.

Shielded Twisted-Pair Cable

Shielded Twisted-Pair (STP) is mainly used in the environment with electrical frequency interference. STP uses a woven cooper braid, a foil wrap between and around the wire pairs, and internal twisting of the pairs to provide a high degree of protection from outside electric currents. This kind of cable is mainly used with the networks using Token Ring topology.

?  Coaxial Cable

Coaxial cable has copper core (the inner conductor) with the outer cylindrical shell for the insulation. The outer cooper shield just under the shell is the second conductor, which keeps the inner conductor away from outside electric currents. The design of coaxial cable prevents the distortion and thus has very less interference.

?  Fiber Optic Cables

Fiber optic cables have become more popular then any other cables. It is relatively thinner compared to twisted pair. Fiber optic consists of glass core in centre surrounded by several layers of protective material. It transmits light rather then the electronic signals eliminating the problem of electronic interference or the distortion. With the help of fiber optic cables it is possible to connection the networks between the two buildings as it is immune to the effects of lighting and moisture. Fiber optics has the capacity of transmitting signals over longer distance at grater speed than coaxial and twisted pair. This allows broadening the communication possibilities of including the voice and video conferencing and interactive services.

Radiated Media

Radiated media are those in which the message is broadcasted through the air. One of the most common examples of the radiated media is radio. And the other types of the radiated media are infrared transmission, microwave and satellites.

Infrared transmission uses low-frequency light wave to carry the data through the air on a direct line-of-sight path between two points. We all use this technology every day while operating remote controls. The remote controls use the same technology. It is prone to interference, particularly from water, smoke and moisture that obscure the light transmission.

A microwave is a very high-frequency radio communication beam that is transmitted over a direct line-of-sight path between any two points. It is a very short wavelength. Microwave performs the same function as cables through-the-air instead of cables. In transmission with the microwave one microwave dish antenna transmits the data to the other nearby antennas. The distance between two antennas can be between 25 to 30 miles.

Transmission using satellite is similar to transmission through microwave. The only difference is instead of transmitting to another nearby microwave dish, it transmits to a satellite which is 500 to 22,500 miles in space. The only problem with the satellite transmission is the delay due to transmission from Earth to space and back from space to Earth.

Media selection

After looking at various media for communication a question arise that which media to select? To find out we will have to keep in mind some criteria for the selection of the best suitable media. Before we select the media for communication we should always try and find out following facts:

Type of network: : It is the major consideration, because some media only support specific type of network. If we select coaxial cable for WAN then it will come up with the problems. Although some old WANs still use twisted pair but is not suitable.

Cost: It is a very import factor. Cost goes on changing as the new technologies coming in the market and the competition among the vendors. If there is a option for selection from two or more we can select on which is economical. The cost normally depends on the size of the network and the distance as well.

Transmission distance: It one of the related factors of selection as we need to consider that each media has works effectively in some specific distance. Like twisted pair and radio can transmit up to a distance of 300 meters whereas coaxial cable and infrared cover the up to 500 meters of distance.

Security: Security of the network can be preliminary found by determining whether media is guided or radiated. Guided media(twisted pair, coaxial cable and fiber optic cables) are more secured compared to radiated media(Radio, infrared, microwave or the satellite) as the waves in the air can be easily intercepted during transmission.

Error rate: It another important factor to be considered while selection of the media. As media should be such which has very less error rates and is efficient.

Transmission speed: The speed of all the media differ from one another which makes them unique in themselves. We should not only look at the speed but also the other factors should be considered while selection. The speed should be in selected in combination with the business requirements, as some may need media with the high speed where as others may not need very high capacity media.

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