Chapter 12
DATA COMMUNICATION
AND NETWORKING
Communication
sending or receiving information
Beating of drums
Mirrors reflecting sunlight
Homing pigeons
Telegraph, telephone
Computers …
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•
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Data Communication
Data Communication
DATA COMMUNICATION
• Exchange of data between two devices
• wired or wireless transmission medium
Transfer of data
Method of transfer
Preservation of the
data during the
transfer process
Communication system (collection of hardware, software …)
Delivery
• The system must
deliver data to the
correct or the
intended
destination.
Accuracy
• The system must
deliver data
accurately (error
free).
Timeliness
• The system must
deliver data in a
timely manner
without enough
time lags.
Five components of a data
communication System
1. Message
• It is the information to be communicated. Popular forms of information include text, pictures, audio,
video etc.
2. Sender
• It is the device which sends the data messages. It can be a computer, workstation, telephone
handset etc.
3. Receiver
• It is the device which receives the data messages. It can be a computer, workstation, telephone
handset etc.
4. Transmission Medium
• It is the physical path by which a message travels from sender to receiver. Some examples include
twisted-pair wire, coaxial cable, radiowaves etc.
5. Protocol
• It is a set of rules that governs the data communications. It represents an agreement between the
communicating devices. Without a protocol, two devices may be connected but not communicating.
Data Transmission Modes
Simplex
• Data in a simplex channel is always one way. Simplex
channels are not often used because it is not possible
to send back error or control signals to the transmit
end. An example of a simplex channel in a computer
system is the interface between the keyboard and the
computer, in that key codes need only be sent one
way from the keyboard to the computer system.
Half Duplex
• A half duplex channel can send and receive, but not at
the same time. Its like a one-lane bridge where two
way traffic must give way in order to cross. Only one
end transmits at a time, the other end receives.
Full Duplex
• Data can travel in both directions simultaneously.
There is no need to switch from transmit to receive
mode like in half duplex. Its like a two lane bridge on
a two-lane highway.
Analog & Digital Transmission
Analog
• information changes continuously
and can take on many different
values. An analog clock’s hands
move constantly, displaying time
on a continuous scale.
Digital
• information is characterized by
discrete states. A light bulb, for
example, is on or off. A digital
clock represents the time in oneminute intervals and doesn’t
change its numbers again until
the next minute. A digital clock
can represent exact minutes but
not the seconds that pass in
between.
Analog & Digital Transmission …
Analog
Signals- Sine waves
Amplitude
Frequency
Wavelength
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Digital
Data Communication Measurement
Narrowband Services
64 Kbps or less channels
Wideband Services
1.5 Mbps to 45 Mbps (North American)
2 Mbps to 34 Mbps (International)
Broadband Services
45 Mbps or greater (North American)
34 Mbps or greater (International)
It Changes
Transmission Media
Radio Frequency Propogation
Modulation
Multiplexing
Multiplexing …
Synchronization- Controlling time
Asynchronous Transmission
Each character of data is treated independently
Synchronous Transmission
For sending large blocks of data
Control schemes
Character-oriented
Bit-oriented
Switching
…