Undergraduate course content: Introduction: Types and sources of data, communication models, standards. Data transmission: techniques, transmission media and characteristics. Information theory: Information sources, information measure, entropy, source codes. Line codes: characteristics, return-to-zero and non-return-to-zero signaling, bipolar alternate mark inversion, code (radix, redundancy and efficiency), important codes in current use, frequency spectra characteristics of common line codes, receiver clock synchronization, optical fiber systems, scramblers. Modems: characteristics, modulation, equalization, control, V-standards. Error Control: Transmission impairments, forward error control, linear block codes, feedback error control.

1. Dr. Randa Elanwar
2012-2013

2.  Introduction: Types and sources of data,
communication models, standards.
 Data transmission: techniques, transmission
media and characteristics.
 Information theory: Information sources,
information measure, entropy, source codes.
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Data Communications Dr. Randa Elanwar 2012-2013

3.  Line codes: characteristics, return-to-zero and
non-return-to-zero signaling, bipolar alternate
mark inversion, code (radix, redundancy and
efficiency), important codes in current use,
frequency spectra characteristics of common
line codes, receiver clock synchronization,
optical fiber systems, scramblers.
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Data Communications Dr. Randa Elanwar 2012-2013

4.  Modems: characteristics, modulation,
equalization, control, V-standards.
 Error Control: Transmission impairments,
forward error control, linear block codes,
feedback error control.
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5.  Communication enters our daily lives in so
many different ways:
 The telephones in our hands, the radios and
televisions in our living rooms, the computer
terminals with access to the internet in our
offices and homes, and our newspapers are all
capable of communication from every corner of
the globe.
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6.  The list of applications involving the use of
communication is almost endless:
 It provides the senses for ships on the high seas,
aircraft in flight, and rockets and satellites in space.
 It keeps a weather forecaster continuously informed
of conditions
 A cellular keeps a car driver in touch with the office
or home miles away.
 Electrical communication is reliable,
economical and can transmit information over
very long distances and at the speed of light.
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7.  There are four important sources of information:
speech, music, images and computer data.
 This information is carried from source to
destination by a signal.
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8.  A signal is a single valued function of time that
describes a set of information or data.
 The signal can be one-dimensional as in case of
speech, music or computer data; two-
dimensional as in case of pictures; three
dimensional as in case of video data.
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9.  Data is either digital or analog.
 Digital data is constructed with a finite number of
symbols.
 For example, printed language consists of 26 letters, 10
numbers and several punctuation marks. Thus a text is a
digital message constructed from about 50 symbols.
 Another example, a Morse-coded telegraph message is a
digital message constructed from a set of only two
symbols (mark and space). It is therefore, a binary
message, implying only two symbols. A digital message
constructed with M symbols is called M-ary message.
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Data Communications Dr. Randa Elanwar 2012-2013

10.  The main characteristics for digital signal:
Amplitude, frequency , pulse width)
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11.  Analog data is constructed by values that vary
over a continuous range.
 For example, the temperature and the
atmospheric pressure can have infinite number
of possible values.
 Another example, the speech waveform has
amplitudes that vary over a continuous range.
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12.  The main characteristics for analog signal:
Amplitude, Frequency, phase angle)
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13.  Frequency is the rate of
change with respect to time.
 Change in a short span of
time means high frequency.
 Change over a long span of
time means low frequency.
 Phase describes the position
of the waveform relative to
time 0.
 Two signals with the same
phase and frequency, but
different amplitudes
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14.  Two signals
with the same
amplitude and
phase, but
different
frequencies
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15.  Three sine
waves with the
same
amplitude and
frequency, but
different
phases
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16.  The purpose of a communication system is to
deliver a message signal from an information
source in a recognizable form to a user
destination, with the source and the user being
physically separated from each other.
 The components of a communication system
are as follows:
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17.  A typical communication system components
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18.  The source originates a message or data.
 If the data is non-electrical (speech, video, etc.)
it must be converted by an input transducer
into an electrical waveform referred to as the
baseband signal or message signal.
 The transmitter modifies the baseband signal
for efficient transmission.
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19.  The channel is a medium such as wire, coaxial
cable, a wave guide, an optical fiber, or a radio link
through which the transmitter output is sent.
 The receiver reprocesses the signal received from
the channel by undoing (reversing) the signal
modifications made at the transmitter and the
channel.
 The receiver output is fed to the output transducer
which converts the electrical signal to its original
form (the message).
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20.  The destination is the unit to which the
message is communicated.
 Digital messages are transmitted by using a
finite set of electrical waveforms.
 For example, in Morse code, a mark can be
transmitted by an electrical pulse of amplitude
A/2 and a space can be transmitted by an
electrical pulse of amplitude -A/2 (square
pulse).
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21.  The channel acts partly as a filter to attenuate
the signal and distort its waveform.
 The signal attenuation increases with the
length of the channel.
 Such distortion can be corrected (with limits)
by a complementary equalizer at the receiver.
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22.  The waveform is distorted because of different
amounts of attenuation and phase shifts.
 For example, a square pulse is rounded or
“spread out” during the transmission. This
type of distortion is called linear distortion.
 The channel may also cause nonlinear
distortion through attenuation that varies with
the signal amplitude.
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23.  The signal is also contaminated along its path
by undesirable signals, called noise, which are
random and unpredictable signals from causes
external and internal.
 As shown in figure, (a) transmitted signal, (b)
received distorted signal (without noise), (c)
received distorted signal (with noise), (d)
regenerated signal.
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25.  Digital signals are more noise immune than analog
signals.
 Considering the binary case: two symbols as
square pulses of amplitudes A/2, -A/2. The only
decision to construct (regenerate) the signal at the
receiver is the selection between two possible
pulses received, not the details of the pulse
(waveform) shape.
 The decision is not affected if the pulses are
distorted or noisy.
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26.  In contrast, the waveform in an analog message
is important, and even a slight distortion or
interference in the waveform will cause an
error in the regenerated signal.
 Thus we sometimes tend to make Analog-to-
Digital conversion.
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27.  In general, there are two basic modes of data
communication:
1. Broadcasting, which involves the use of a
single powerful transmitter and numerous
receivers, here information signals flow only in
one direction (example: radio and television).
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28. 2. Point-to-point communication, where
communication takes place between a single
transmitter and a receiver. There is usually a
bidirectional flow of information signals
(example: telephones).
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29.  There are also two fundamental techniques of data
transmission: synchronous transmission and
asynchronous transmission.
 Example: the text prepared on a PC is usually
stored and then transmitted over a communication
channel (e.g., a telephone channel) with a single
character being sent at a time. This form of data
transmission is called asynchronous transmission,
as opposed to synchronous transmission in which
the whole sequence of characters is sent over the
channel in one long transmission.
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30.  Communication Networks
 A communication network
consists of an
interconnection of a number
of routers made up of
intelligent processors that
route data through the
network. Each router has
one or more hosts attached
to it. Hosts are the devices
that communicate with one
another.
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31.  Communication Networks
 The telephone network is an example of a
communication network. It uses a circuit as a
communication path between two hosts.
 The circuit consists of a connected sequence of
links from source to destination.
 The circuit remains uninterrupted for the duration
of transmission i.e. all resources allocated at the
connection time are owned to the two hosts until
the circuit is disconnected. This is referred to as
circuit switching.
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32.  Communication Networks
 In circuit switching, the communication link is
shared between the different sessions using
that link via fixed allocation of resources.
 On the other hand, in packet switching resource
sharing is done on demand. Thus, the link is
more efficiently utilized.
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33.  Communication Networks
 In packet switching, the network works on “store
and forward” principle. Any message larger than a
specified size is subdivided prior to transmission
into segments called packets.
 The original message is reassembled at the
destination. Accordingly, packet switching is more
suitable for computer communication
environment. However, the use of packet
switching requires the careful control on user
demands; otherwise, the network may be seriously
abused.
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34.  Communication Channels
 The transmission of information across a
communication network is accomplished in the
physical layer by means of a communication
channel.
 The communication channel properties
determine both the information-carrying
capacity of the system and the quality of
service offered by the system.
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35.  Communication Channels
 In communication systems, two primary
resources are employed: transmitted power and
channel bandwidth.
 We may classify communication channels as
bandwidth limited or power limited. A general
system design objective is to use these two
resources as efficiently as possible.
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36.  Communication Channels
 The channel bandwidth is the band of
frequencies allocated for the transmission of
the message signal.
 The transmitted power is the average power of
the transmitted signal. Increasing the signal
power reduces the effect of channel noise and
the information is received more accurately. A
larger Signal-to-Noise ratio (SNR) allows
transmission over longer distance.
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37.  Communication Channels
 The limitation imposed on communication by the
channel bandwidth and the SNR is determined by
Shannon’s equation:
C = B log2(1+SNR)
 C, the channel capacity, is the rate of information
transmitted per second, in other words, the
maximum number of binary symbols (bits) that
can be transmitted per second with probability of
error close to zero.
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38.  Communication Channels
 We have two basic groups of communication
channels: channels based on guided propagation
and those based on free propagation.
 The first group includes telephone channels,
coaxial cables, and optical fibers. The second
group includes wireless broadcast channels,
mobile radio channels and satellite channels.
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39.  Communication Channels
 The telephone channel: the message source is the
sound of the speaker’s voice and the destination is
the listener’s ear.
 The telephone channel supports only the
transmission of electrical signals. Accordingly, we
have transducers at both the transmitting and
receiving ends.
 The telephone channel is bandwidth-limited
channel due to the requirement of sharing the
channel among multiple users at the same time.
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40.  Communication Channels
 The telephone channel is built using twisted
pairs (two copper conductors) for signal
transmission. Twisted pairs are naturally
susceptible to electromagnetic interference.
Thus it is suitable only for point-to-point
services.
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41.  Communication Channels
 The coaxial cable consists of an inner conductor
and an outer conductor separated by a
dielectric insulating material.
 It is more immune to electromagnetic
interference than twisted pairs and have much
higher bandwidth thus supports the
transmission of digital data at much higher bit
rates.
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42.  Communication Channels
 Thus it is suitable for multiple access media
like local area networks (LANs).
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43.  Communication Channels
 The optical fiber is a dielectric wave guide
made of silica glass that transports light signals
from one place to another just like twisted pairs
and coaxial cables transport electrical signals.
 Optical fibers have enormous bandwidth, low
transmission losses, immunity to
electromagnetic interference and high
flexibility.
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44.  Communication Channels
 Thus it is suitable for very long distance
communications.
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45.  Communication Channels
 Wireless broadcast channels support the
transmission of radio and television signals in
the free space.
 The transmission originates from transmitter
antenna in the direction and line of sight to the
receiving antenna to avoid diffraction and
scattering.
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46.  Communication Channels
 Mobile radio channels support the
transmission in case the transmitter or the
receiver is in motion.
 Sometimes there is no line of sight path and
signals are scattered by buildings. Thus, radio
waves reach their destination from different
directions and with different time delays.
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47.  Communication Channels
 Satellite channel enables access to remote areas
not covered by conventional cables or fiber
communications.
 It provides broad-area coverage, reliable
transmission links and wide transmission
bandwidths but is power limited.
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