Laboratory of Physical Layer
Mux/Demux
Physical Layer
Physical layer includes transmission media that
is connected to the physical layer.
• The first introduces the entities involved in the
physical layer.
• Transmission method consists of digital and
analog.
• Bandwidth Utilization: How to use the
available bandwidth by using Multiplexing
and Spectrum Spreading.
• Switching can occur in any layer.
Intro. Of Physical Layer
Physical layer moves data in the form of
electromagnetic signals across a
transmission medium.
• Data and signals can be either analog or
digital.
– Analog refers to an entity that is
continuous;
– digital refers to an entity that is discrete.
Intro. Of Physical Layer
• Periodic analog signals can be used in
data communication.
– simple and
– composite signals.
• The attributes of analog signals consist of:
• period,
• frequency, and
• phase.
Intro. Of Physical Layer
Nonperiodic digital signals can be used in
data communication.
• The attributes of a digital signal such as:
– bit rate and bit length
• How digital data can be sent using analog
signals.
• Baseband and broadband transmission.
Intro. Of Physical Layer
Transmission impairment.
1. attenuation,
2. distortion, and
3. noise
How they can impair a signal?
Intro. Of Physical Layer
How many bits per second we can send with the available
channel.
Data rate depends on three factors:
• The bandwidth available
• The level of the signals we use
• The quality of the channel (the level of noise)
Two theoretical formulas were developed to calculate
the data rate:
1. Nyquist for a noiseless channel,
2. Shannon for a noisy channel.
Multiplexing
Data link with limited bandwidths.
Bandwidth utilization:
• multiplexing and
• spectrum spreading
Link = physical path
Channel = the portion of a link that carries a transmission
between a given pair of lines
(One link can have many n channels)
N lines share one link
Multiplexing
8
Multiplexing Techniques
FDM – Example
Wavelength-Division Multiplexing
Time-Division Multiplexing
The link is shown sectioned by time rather than by
frequency. In the figure, portions of signals 1,2,3,
and 4 occupy the link sequentially.
Multiplexer (Mux)
• Selects between one of N inputs to connect to
output
• log2N-bit select input – control input
• Example:
2:1 Mux
S
0
1
2:1 multiplexer
symbol
Y
D0
D1
Select input S
S
0
0
0
0
1
1
1
1
D1
0
0
1
1
0
0
1
1
D0
0
1
0
1
0
1
0
1
Y
0
1
0
1
0
0
1
1
Truth table
Multiplexer Implementations
• Logic gates
– Sum-of-products form