2. Data communications refers to the transmission of this
digital data between two or more computers and a computer
network or data network is a telecommunications network
that allows computers to exchange data. The physical
connection between networked computing devices is
established using either cable media or wireless media.
4. 1. Guided media are more commonly known as
wiredmedia, or those media in which electrical or
optical signals are transmitted through a cables or
wires.
5. 2.Unguided media are more commonly known
as wireless media, in which electromagnetic
signals are sent through space with no
direction.
6. Twisted Pair
The two wires are typically ``twisted'' together in a helix to reduce
interference between the two conductors as shown in Fig.2.2.2.
Twisting decreases the crosstalk interference between adjacent
pairs in a cable. Typically, a number of pairs are bundled together
into a cable by wrapping them in a tough protective sheath.
7. • Can carry both analog and digital signals. Actually, they carry
only analog signals. However, the ``analog'' signals can very
closely correspond to the square waves representing bits, so
we often think of them as carrying digital data.
• Data rates of several Mbps common.
• Spans distances of several kilometers.
8. Base band Coaxial
With ``coax'', the medium consists of a copper core
surrounded by insulating material and a braided outer
conductor as shown in Fig. 2.2.3. The term base band
indicates digital transmission (as opposed to broadband
analog).
9. fiber optic
In fiber optic technology, the medium consists of a hair-
width strand of silicon or glass, and the signal consists of
pulses of light. For instance, a pulse of light means ``1'', lack
of pulse means ``0''. It has a cylindrical shape and consists of
three concentric sections: the core, the cladding, and the
jacket as shown in Fig. 2.2.4.
10.
11.
12. 2.Unguided media are more commonly known
as wireless media, in which electromagnetic
signals are sent through space with no
direction.
13. Satellite communication is based on ideas similar to those
used for line-of-sight. A communication satellite is
essentially a big microwave repeater or relay station in the
sky. Microwave signals from a ground station is picked up by
a transponder, amplifies the signal and rebroadcasts it in
another frequency, which can be received by ground stations
at long distances as shown in Fig. 2.2.7.
14.
15.
16. Infrared radiation, or simply infrared or IR,
is electromagnetic radiation (EMR) with
longer wavelengths than those of visible light, and is
therefore invisible, although it is sometimes loosely
called infrared light. It extends from the nominal red edge of
the visible spectrum at 700 nanometers (frequency 430 THz),
to 1000000 nm (300 GHz)
17.
18. Its frequency is between 10 kHz to 1GHz. It is simple to install
and has high attenuation.These waves are used for multicast
communications.
19. Types of Propogation
RadioTransmission utilizes different types of
propogation :
Troposphere :The lowest portion of earth’s
atmosphere extending outward approximately
30 miles from the earth’s surface. Clouds, jet
planes, wind is found here.
Ionosphere :The layer of the atmosphere above
troposphere, but below space. Contains
electrically charged particles.
20. Transmission mode means transferring of
data between two devices. It is also called
communication mode.These modes direct
the direction of flow of information.
21. There are three types of transmission mode.
They are :
Simplex Mode
Half duplex Mode
Full duplex Mode
22. In this type of transmission mode data can be sent
only through one direction i.e. communication is
unidirectional. We cannot send a message back to
the sender. Unidirectional communication is done in
Simplex Systems.
23. In half duplex system we can send data in both
directions but it is done one at a time that is when
the sender is sending the data then at that time we
can’t send the sender our message.The data is sent
in one direction.
24. In full duplex system we can send data in both directions as it
is bidirectional. Data can be sent in both directions
simultaneously. We can send as well as we receive the data.
