Transmission Media
} Transmission
medium is a channel through which data or signals can be
transmitted from sender to receiver.
} Data
is transmitted through the electromagnetic signals.
} Transmission
media are also called communication channels.
Guided Media
} It
is a wired transmission media, in which data signals are guided along a
physical path i.e. within a wire.
} Also
known as Bounded or wired media.
} Examples
are Twisted Pair Cable, Coaxial cable and fiber optic cable.
Twisted Pair Cable
} A
pair of wires which are made of copper and are twisted with each other is known
as twisted pair cable.
} A
set of four pairs of twisted wires are bundled to form cable.
} The
wires are twisted to reduce cross talk and electrical interference.
} It
was invented by Alexander Graham Bell in 1881.
} Its
types are :
◦
Unshielded Twisted Pair Cable (UTP)
◦
Shielded Twisted Pair Cable (STP)
Unshielded Twisted Pair Cable (UTP)
} The
unshielded twisted pair cable is a Guided Transmission Media, which is
used for transmitting both data and voice.
} It
consists of 4 pairs of colour-coded wires twisted around each other.
} The
wires are twisted to prevent electromagnetic interference (cross talk)
} Cat
5 cable with RJ-45 connector is commonly used with unshielded twisted pair
Shielded Twisted Pair Cable (STP)
} The
shielded twisted pair cable is a Guided Transmission Media , which is quite
expensive than unshielded twisted pair cable.
} It
has a foil shield that covers the wires.
} The
foil shield adds a layer of protection against electro-magnetic interference
leaking into and out of the cable.
} Shielded
Twisted Pair Cable are more expensive than Unshielded Twisted Pair Cable, but
less susceptible to noise.
Co-axial
Cable
} A
cable which is used with single ended single reference where the central
conductor carries the data signal is called co-axial cable.
} The
connectors used with co-axial cables are BNC, T-connectors and terminators in
bus topology.
} 10
Mbps is the maximum speed of co-axial cable.
} Coaxial
cable is used in cable television.
} It
is preferred for long distance telephone lines as well.
Fiber
Optic Cable
} Fiber
optics cable is one of the costlier cables used in data communication which
uses light to carry a data signal through the cable.
} The
connectors used in fiber optics are Screw Mounted Adaptors (SMA), Spring-loaded
Twist (ST), SC and FC.
} It
is costlier to maintain, produce and install.
} Fiber-optic
cable do not get affected by electromagnetic interference.
} Works
for both analog as well as digital signals.
} Point
to point one way communication generally uses the cable.
Unguided Media
} Unbounded
media are wireless media that does not require any physical medium to transmit
electromagnetic signals.
} The
electromagnetic signals are broadcasted through air to everyone instead of
cables.
} e.g.:
radio waves, micro waves and infrared waves.
Radio Wave
} It
is a form of wireless communications in which signals are sent through radio
frequency waves.
} It
provides low bandwidth for data communication.
} The radio
waves are generated easily; they are low-frequency signals and
can travel a long distance.
} The
radio waves can penetrate through the buildings.
} Frequency
Range:3KHz – 1GHz.
} AM
and FM radios and cordless phones use Radiowaves for transmission.
Microwave
} It
is a form of wireless communication in which data signals are sent through
pulses of electromagnetic energy.
} The
microwave has a frequency higher than the radio waves.
} The microwaves are
transmitted in a straight line and hence require the line-of-sight
transmission.
} More
the taller are antennas longer is the distance covered by the signal.
} Frequency
Range:1GHz – 300GHz.
} Microwave
are used for telephone communication mobile phones, television distribution,
etc.
Infrared
} Infrared
waves are used for short range communication.
} Like,
the remote control for televisions, VCRs, wireless mouse, keyboard, printer,
etc. uses infrared waves.
} It
can not penetrate (enter) through obstacles.
} Frequency
Range:300GHz – 400THz.
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