Signals
|
Need
For Signals
o One of the major concerns of Physical
layer is moving information in the form
of
electromagnetic signals across a TX medium
o Information can be voice, image, numeric
data, characters or any message that
is
readable and has meaning to the destination user (human or m/c)
o Generally, the info usable to a person or
application is not in a form that can
be
transmitted over a network
o For
Example, you cannot
roll up a
photograph, insert it
into the wire
and
transmit
it across the city
o You can transmit however an encoded
description of the photograph
o The binary digits must be converted into
a form that TX. Medium can accept
o TX.
Media work by
conducting energy along
a physical path.
So the data
stream
of 1s and 0s must be turned into energy in the form of EM signals
™ Analog and Digital
o Both data and signals that represent them
can take either analog or digital form
ANALOG
|
Analog
refers to something that is continuous in time
Continuous- A
set of specific
points of data
and all possible
points b/w
them
|
DIGITAL
|
•
•
|
Digital refers
to something that is discrete
Discrete- A set of
specific points of data with no points in between
|
o Data can be Analog or Digital
Example of ANALOG Data is Human voice
When somebody speaks, a continuous wave is
created in the air.
This
can be captured
by a Microphone
and converted to
an Analog
Signal
An
example of DIGITAL
data is Data
stored in the
memory of a
computer
in the form of 1s and 0s. It is usually converted to a digital
signal when
it is transferred
from one position
to the other
inside or
outside
the computer
o Signals can be Analog or Digital
™ ANALOG Signal
|
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