Computer Science XII

Transmission Media or Communication Media or Network Media

Communication media is the pathway or channel along which the signals or data can be transmitted from one point to another. The signal transmitted from one device to another is through electromagnetic signals. It includes voice, radio waves, infrared light etc. The transmission media is divided into two types:
1) Guided Media:
In guided media is a media that uses a transmission carrier to send data signals through a contained conductor. This conductor can be a metal wire through which electricity flows or a glass strand through which pulses of light flows. The different types of guided media are:

a). Twisted Pair:
Twisted pair cable is the oldest and common medium of transmission. Twisted pair cable consists of two insulated strands of copper wire twisted around each other. There are two types of twisted pair cable. There are:

i). Unshielded Twisted Pair (UTP):
UTP cable consists of a number of twisted pairs of wires with a simple plastic casing. UTP is commonly used in telephone system. It is suitable for both data and voice transmission. It comes in different categories (cat 1 to cat 7). The bandwidth of the cables depends upon the category of the cable. UTP is good for noise rejection and it covers a maximum distance of 100m.

ii). Shielded Twisted Pair (STP)
The STP cable is similar in construction to UTP except that the twisted pairs are enclosed in a woven copper and foil wrap shield for providing extra protection from external interference. STP is more difficult to install than UTP and Coaxial cable. It covers shorter distance than UTP, but it has better noise rejection capacity. The STP is more costlier than UTP cables.

b). Coaxial cable:
Coaxial cable (commonly called “coax”) is made of two conductors that share a common axis, hence the same (“co”, “axis”). Typically, the center of the cable is a relatively stiff solid copper wire or stranded wire encased in insulating plastic foam. The foam is surrounded by the second conductor, a wire mesh tube, which serves as a shield from electromagnetic interference (EMI). The coaxial cables are used in communication networks with single ended single reference where the central conductor carries the data signals. The Connectors used in Coaxial cable are BNC, T-connector and terminals.

c). Fiber Optics:
Fiber-optic cable is made of a light conducting glass or plastic core surrounded by more glass called cladding and a tough (hard) outer cover. A fiber optic consists of a bundle of glass threads, each of which is capable of transmitting message modulated onto light waves. Fiber optics uses light signals rather than electricity, so it offers high bandwidth and greatest distance of any transmission system. The main disadvantage of fiber optics are; it is costlier to produce, maintain and install. The connectors used in fiber optics are Screw Mounted Adaptors (SMA), Spring-loaded Twist (ST), SC and FC.

2) Unguided Media:
In unguided media, the data signals flows through the air instead of cables. It includes wireless transmission methods such as radio frequency, infrared transmission, microwaves and others.

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