Data and Computer
Communications
Tenth Edition
by William Stallings

Data Transmission
CHAPTER 3

Contents
3.1
Concepts and Terminology
3.2
Analogue and Digital Data Transmission
3.3
Transmission Impairments
3.4
Channel Capacity

“I have been trying to prove the following theorem: for any operators
T,R the length of an arbitrary message f1 multiplied by its essential
spectrum and divided by the distortion of the system is less than a
certain constant times the time of transmission of F multiplied by its
essential spectrum width or—roughly speaking—it is impossible to
reduce bandwidth times transmission time for a given distortion.
This seems to be true although I do not have a general proof as
yet.”
—Letter to Vannevar Bush,
February 16, 1939,
from Claude Shannon

Transmission Terminology
Data transmission occurs between transmitter
and receiver over some transmission medium
Communication
is in the form of
electromagnetic
waves
Guided
media
Twisted pair,
coaxial cable,
optical fiber
Unguided
media
(wireless)
Propagation
through air,
vacuum, and
seawater

Transmission
Terminology
•
No intermediate devices other than
amplifiers or repeaters used to
increase signal strength
Direct link
Direct link
•
Direct link between two devices
•
Are the only 2 devices sharing
medium
Point-to-point
Point-to-point
•
More than two devices share the
same medium
Multi-point
Multi-point

Transmission
Terminology
Simplex
Signals are transmitted in only one direction
One station is transmitter and the other is
receiver
Half Duplex
Both stations transmit, but only one at a time
Full Duplex
Both stations may transmit simultaneously
The medium is carrying signals in both directions
at the same time

Amplitude
(volts)
Time
(a) Analog
Amplitude
(volts)
Time
(b) Digital
Figure 3.1
Analog and Digital Waveforms

Amplitude (volts)
A
Time
0
–A
Amplitude (volts)
A
Time
0
–A
( a ) S i n e w
a v e
( b ) S q u a r e w
a v e
F
i g u r e 3 . 2 E
x a m
p l e s o f P
e r i o d i c S i g n a l s
period =
T
= 1/
f
period =
T
= 1/
f

Sine Wave
Is the fundamental periodic signal
Can be represented by three parameters
Peak amplitude (
A
)
•
Maximum value or strength of the signal over time
•
Typically measured in volts
Frequency (
f
)
•
Rate at which the signal repeats
•
Hertz (Hz) or cycles per second
•
Period (
T
) is the amount of time for one repetition
•
T =
1/
f
Phase (
)
•
Relative position in time within a single period of signal

Wavelength (
)
The wavelength of
a signal is the
distance occupied
by a single cycle
The wavelength of
a signal is the
distance occupied
by a single cycle
Can also be stated as the
distance between two
points of corresponding
phase of two consecutive
cycles
Can also be stated as the
distance between two
points of corresponding
phase of two consecutive
cycles
Assuming signal
velocity
v
, then the
wavelength is related
to the period
as
= vT
Assuming signal
velocity
v
, then the
wavelength is related
to the period
as
= vT
Or
equivalently
f = v

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- Fall '18
- Jarlath Nolan
- Digital Signal Processing