Page 53 - DCAP406_DCAP_207_Computer Networks

Computer Networks/Networks

Notes depends upon the type of energy being transmitted. Each form of energy has different properties
and requirements for transmission. This requires special hardware for data encoding and
connection to transmission medium. Media can be copper, glass and air, etc.

4.1 Wireless Transmission

Wireless transmission systems do not make use of a physical conductor, or guide, to bind the
signal. In this case, data are transmitted using electromagnetic waves. Therefore, they are also
known as unguided or unbounded systems. Energy travels through the air rather than copper or
glass. Hence the term radiated often is applied to wireless transmission. Finally, such systems
employ electromagnetic energy in the form of radio or light waves that are transmitted and
received across space, and are referred to as airwave systems. The transmission systems addressed
under this category include microwave, satellite and infrared. There are different techniques to
convert the data suitable for this mode of communication. Conceptually similar to radio, TV,
cellular phones, radio waves can travel through walls and through an entire building. They can
travel for long distance using satellite communication or short distance using wireless
communication.
Use of this technology for delivery of real time applications like multimedia material should be
treated carefully, because radio links are susceptible to fading, interference, random delays, etc.
Non-real time use of this technology is likely to perform as well as current Ethernet LANs.

4.1.1 Radio

It is a technique where data is transmitted using radio waves and therefore energy travels
through the air rather than copper or glass. Conceptually, radio, TV, cellular phones, etc. uses
radio transmission in one form or another. The radio waves can travel through walls and
through an entire building. Depending upon the frequency, they can travel long distance or
short distance. Satellite relay is the one example of long distance communication. Therefore,
each frequency range is divided into different bands, which has a specific range of frequencies in
the Radio Frequency (RF) spectrum. The RF is divided in different ranges starting from Very
Low Frequencies (VLF) to Extremely High Frequencies (EHF). Figure 4.1 shows each band with
a defined upper and lower frequency limit.

Figure 4.1: Radio Frequency Range and Types of Transmission Media
24
10 0 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 ....
Radio Micro Infrared U X-ray Gamma
wave V ray

Visible

10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 10 14 10 15
Twisted Satellite
Pair Fiber

Coaxial cable
Microwave

LF MF HF VHF UHF SHF

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