CSC 242
Introduction to
Telecommunications Systems
Lecture # 1
Dr. Ehsan Munir
Department of Computer Science
COMSATS Institute of Information Technology
What is Communication
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When we communicate we share
information
Local Communication
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Face to face
Remote Communication
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Over distance
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DATA COMMUNICATIONS
Data communications are the exchange of data between
two devices via some form of transmission medium such
as a wire cable. The word data refers to information
presented in whatever form is agreed upon by the parties
creating and using the data.
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Data Communication System

For data communication to occur,
communicating devices must be a part
of a system made up of some specific
kind of hardware and software. This
system is known as “DC System”
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DC System Components
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Message
Sender
Receiver
Transmission Medium
Protocol
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Figure Five components of data communication
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Factors Effecting DC System
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Delivery
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Accuracy
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Deliver data accurately
Timeliness
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Deliver data to correct destination
Deliver data in a timely manner
Jitter
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Variation in packet arrival time
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Figure Data flow (simplex, half-duplex, and full-duplex)
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Data Flow
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Simplex
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Half duplex
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Transmission in one direction. Example Television
Either direction, but only one way at a time.
Example Walkie-talkies
Full duplex
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Both directions at the same time. Example
Phones.
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What is Telecommunication
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Tele is Greek word, meaning “far off”
Webster calls it communications at a
distance
The IEEE Standard Dictionary defines
telecommunications as the transmission
of signals over long distance,
Science of communicating over distance
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Networks
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A network is a set of devices (nodes)
connected by communication links.
A node can be a computer, printer, or any
other device capable of sending and/or
receiving data generated by other nodes on
the network.
A link is a communication pathway that
transfers data from one device to another
Topology: Arrangement of nodes in a network
specify topology.
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Figure Types of connections: point-to-point and multipoint
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Network Criteria
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Performance
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Reliability
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Throughput: Number of bits transmitted in one
second
Delay: How long it takes a bit of data to travel in
network
Robustness : ability of the network to perform its
function in the face of attack (node failure)
Security
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Unauthorized access
viruses
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Categories of topology
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Figure A bus topology connecting three stations
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Bus Topology
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Single cable connect all computers
Each computer has connector to shared cable
Cable must end with a terminator
Advantages
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Ease of installation
Inexpensive
Works well for small networks
Disadvantages
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Cable break, whole network down
Limited number of devices can be attached
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Figure A star topology connecting four stations
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Star Topology
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All computers attach to central point
The devices are not directly linked to one
another
Advantages
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Ease of installation
Inexpensive (less than mesh)
Robustness
Disadvantages
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Hub fails, whole network down
Costly than bus
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Figure A fully connected mesh topology (five devices)
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Mesh Topology
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Each device connected to every other device
Advantages
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Robustness
Can carry more data
Disadvantages
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Expensive
Difficult to install
Difficult to manage
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Figure A ring topology connecting six stations
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Ring Topology
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Each device connected to two devices
(immediate neighbors)
The signal is passed along the ring in one
direction
Advantages
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Easy to install and reconfigure
Inexpensive (less than mesh)
Disadvantages
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Break in a ring disables the whole network
Unidirectional
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Figure A hybrid topology: a star backbone with three bus networks
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Types of Networks
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Local Area Network (LAN)
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Wide Area Network (WAN)
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Links the nodes in a single office, building or
campus
Links the nodes in states, countries or in the
whole world
Metropolitan Area Network (MAN)
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Between LAN and WAN
Links the nodes in a town or city
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Protocols
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Protocol defines:
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What is communicated
How, it is communicated
When, it is communicated
Elements of a protocol
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Syntax
Semantics
Timing
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Standards
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A standard provides a model for
development that makes it possible for
a product to work regardless of the
individual manufacturer
Standards are essential in:
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Creating/Maintaining open and competitive
market
Guaranteeing National/International
Interoperability
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