1_introduction to network
TRANSCRIPT
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Computer Networks
&
Data Communication
Gamini Wijayarathna
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Recommended Readings
• William A. Shay, “Understanding Data
Communications and Networks”, 2nd Edition,
1999, Brooks/Core Publishing Company.
• Comer Douglas, E. “Internetworking with
TCP/IP”, 3rd Edition, 2000, Prentice-Hall.
• Andrew S. Tanenbaum, “Computer Networks”, 3rd
Edition, 1997, Prentice-Hall, Inc.
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Why Study Communications?
Communication technology has invaded
virtually every aspect of daily life, from
professional and educational uses to
purely recreational ones.
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A Brief History
• The filed of communications is not new:
– For thousands of years people communicated using little
more than words, stone tablets, and smoke signals.
– The primary forms of sending information were based on
the auditory and visual senses.
• Communications changed drastically in 1837,
when Samuel Morse invented the telegraph. This
invention made it possible to send information using
electrical impulses over a copper wire. Messages were
sent by translating each character into a sequence of
long or short electrical impulses (dots and dashes).
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A Brief History (Cont.)
• In 1876 Alexander-Graham Bell took the
telegraph one step further. He showed that a
voice could be converted directly to electrical
energy and transmitted over a wire using
continuously varying voltages. At the wire’s other
end the electrical signals were converted back to
sound.
• During next 70 years the telephone system grew to
the point where the telephone became a common
device in a home.
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A Brief History (Cont.)
• In 1945 - Invention of the first electronic
computer, ENIAC (Electronic Numerical
Integrator and Calculator). It was the first
device that could actually process information
electronically.
• The relation between computers and
communications began to emerge after the
invention of the transistor in 1947. It allowed
smaller and cheaper computers to be built.
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A Brief History (Cont.)
• The new generation of computers that emerged during 1960s made new applications such as processing and routing telephone calls economically feasible.
• Another milestone in electronic communications occurred with the development of the personal computer (PC). The 1980s saw the infusion of millions of PCs into virtually every business, company, school, and organization and into many homes as well. The fact that so many people now had computers generated the need to make information even more easily accessible.
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A Brief History (Cont.)
• The 1990s saw the emergence of the World Wide
Web (WWW), an application that makes
information from around the world easily accessible
from one’s desk. With the click of a mouse button,
computer users can access files, programs, video
clips, and sound bites. Online services such as chat
rooms, bulletin boards, airline reservation systems,
and more. Computers and communications have
progressed to the point where most businesses or
schools can no longer function without them.
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Applications
• Transferring data between computers. LAN
/ WAN communications.
• Telephones /Fax / Cellular phones.
• Televisions.
• Voice and video communications.
• Teleconferencing.
• Information Services.
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Computer Communication
Schematic
Computer A Computer B
Communication
subsystem
Communication
subsystem
Application
process
Application
process
Data communication network
User-to-user
communication
Computer-to-computer
communication
Computer-to-network communication
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Uses of Computer Networks
(for Companies)
• Resource sharing
• High reliability
• Saving money
• Scalability
• Communication medium
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Resource Sharing
Goal is to make all
programs
equipments &
data
available to anyone on the network
without regard to the physical location
of the resource and the user.
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High Reliability
• Multiple copies of files
• Multiple CPUs
For military, banking, air traffic control,
nuclear power plant, and many other
applications, the ability to continue
operating in the face of hardware
problem is of utmost importance.
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Saving Money
• Small computers have a much
better price/performance ratio
than large ones.
• Mainframes are faster than PCs but
they cost a thousand times more.
Mainframes Client – Server Systems
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Client – Server Model
Client Machine Server Machine
Network
Request
Reply
Client
Process
Server
Process
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Scalability
should be replaced by
a large one.
• expensive
• disruption to the users
• new clients and
• new servers
can be added as needed.
Centralized Mainframes Client – Server Systems
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Uses of Computer Networks
(for People)
• Access to remote information
• Person-to-person communication
• Interactive entertainment
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Network Hardware
• Transmission technology
• Scale
Criterions for classifying networks:
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Transmission Technology
• Broadcast networks
• Point-to-point networks
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Scale Interprocess
or distance
Processors
located in same
Example
0.1 m Circuit board Data flow machine
1 m System Multicomputer
10 m Room
Local area network
( LAN )
100 m Building
1 km Campus
10 km City Metropolitan area
network ( MAN )
100 km Country Wide area network
( WAN ) 1,000 km Continent
10,000 km Planet The Internet
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Network Topology
Manner in which network devices are
connected physically.
Devices:
Mainframes, Workstations, File servers,
Printers, Scanners
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Network Topologies
• Bus topology
• Star topology
• Ring topology
• Hybrid topology
• Tree topology
• Complete topology
• Irregular topologies
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Bus Topology
Mainframe
Workstation File server Workstation
File server
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• A single communication line
• Each device has an interface that listens to
the bus and examines its data traffic
• Carrier Sense, Multiple Access with
Collision Detection (CSMA/CD)
Bus Topology (cont.)
Ethernet (IEEE 802.3)
http://www.ieee802.org/3/
- One popular bus network
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• A single communication line
• Each device has an interface that listens to
the bus and examines its data traffic
• Carrier Sense, Multiple Access with
Collision Detection (CSMA/CD)
Bus Topology (cont.)
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Bus Topology (Cont.)
A B
C D E
Cable A Segment
Cable C
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Bus Topology (Cont.)
A B
C D E
No traffic
Send Concurrently
X
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Bus Topology (Cont.)
CSMA/CD
A B
C D E
X
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Star Topology
Cables
Computer
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Star Topology (Cont.)
One station (often a mainframe or file
server) is a logical communication
center
Other stations communicate through it
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Star Topology (Cont.)
A B
C D Z
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Ring Topology Computer
Cables
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Ring Topology (Cont.)
Stations are arranged in a ring
Each station connected directly
only to its two neighbors
Messages pass through all of the
stations in between
(clockwise or counterclockwise)
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Ring Topology (cont.)
A B
C
D
E
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Hybrid Topology
bridge Computer Computer
Computer
bridge
Computer
Computer Computer
Computer
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Tree Topology
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Complete Topology
Cables
Computer
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Irregular Topology
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Local Area Networks ( LANs)
They are widely used to connect
personal computers & workstations in
company offices & factories to
share resources & exchange information.
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Popular LANs
Ethernet (IEEE 802.3)
• Bus topology
• 10 or 100 Mbps (Megabits/Sec.)
Megabit = 1,000,000 bits
but not 1,048,576 (220)
IBM Token Ring (IEEE 802.5)
• Ring topology
• 4 or 16 Mbps
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Metropolitan Area Networks
(MANs)
• Bigger version of LANs
• Normally uses similar technology
• DQDB (IEEE 803.6)
(Distributed Queue Dual Bus)
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Architecture of the DQDB
MAN
Bus A
Bus B
Direction of flow on bus A
Direction of flow on bus A
Head end
Computer 1 Computer 2
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DQDB MAN
Bus A
Bus B
Direction of flow on bus A
Direction of flow on bus A
Head end
Computer 1 Computer 2
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Wide Area Networks (WANs)
Spans a large geographical area
(a country or continent)
Contains a collection of hosts
Hosts are connected by a subnet
(communication subnet)