LECTURE #11
Signals
Need For Signals
oOne of the major concerns of Physical layer is moving information in the form
of electromagnetic signals across a TX medium
oInformation can be voice, image, numeric data, characters or any message that
is readable and has meaning to the destination user (human or m/c)
oGenerally, the info usable to a person or application is not in a form that can
be transmitted over a network
oFor Example, you cannot roll up a photograph, insert it into the wire and
transmit it across the city
oYou can transmit however an encoded description of the photograph
oThe binary digits must be converted into a form that TX. Medium can accept
oTX. 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
oBoth data and signals that represent them can take either analog or digital form
¾ANALOG
• Analog refers to something that is continuous in time
•Continuous– A set of specific points of data and all possible points b/w
them
¾DIGITAL
• Digital refers to something that is discrete
•Discrete– A set of specific points of data with no points in between
oData can be Analog or Digital
9Example of ANALOG Data is Human voice
9When somebody speaks, a continuous wave is created in the air.
9This can be captured by a Microphone and converted to an Analog
Signal
9An 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
oSignals can be Analog or Digital
ANALOG Signal
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