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Lesson - 1
Introduction to Computer Networks and
Data Communications
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Introduction Who today has notused a computer network?
Mass transit, interstate highways, 24-hour bankers, grocery
stores, cable television, pagers, mobile telephones, most
businesses and schools, and other retail outlets can support someform of computer networks.
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The Language of Computer Networks Computer network - an interconnection of computers and
computing equipment using either wires or radio waves over small
or large geographic distances
Local area network - networks that are small in geographic sizespanning a room, building, or campus
Metropolitan area network - networks that serve an area of 3 to
30 miles - approximately the area of a typical city
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The Language of Computer Networks Wide area network - a large network that encompasses parts of
states, multiple states, countries, and the world
Data communications - the transfer of digital or analog data using
digital or analog signals
Voice network - a network that transmits telephone signals
Data network - a network that transmits computer data
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The Language of Computer Networks Telecommunications - the study of telephones and the systems
that transmit telephone signals
Network management - the design, installation, and support of a
network and its hardware and software
Personal area networka network of a few meters, between
wireless devices such as PDAs, laptops, and similar devices.
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The Big Picture of Networks Networks are composed of many devices, including:
workstations (computers and telephones)
network servers
network hubs and switches (bridges)
routers (LAN-WAN and WAN-WAN)
telephone switching gear
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Computer Networks - Basic Configurations Computer terminal-to-mainframe computer
Microcomputer-to-mainframe computer
Microcomputer-to-local area network
Microcomputer-to-Internet
Local area network-to-local area network
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Computer Networks - Basic Configurations Local area network-to-metropolitan area network
Personal area network-to-workstation
Local area network-to-wide area network
Sensor-to-local area network
Satellite and microwave
Wireless telephone and wired telephone-to-network
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Basic ConfigurationsComputer terminal
to mainframe computer
Predominant form in 60s and 70s.
Still used in many types of businesses for data entry and data
retrieval.
Usually involves a low-speed connection.
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Basic ConfigurationsMicrocomputer-to-
Local Area NetworkHighly common throughout business and academic environments,
and now even homes
Typically a medium- to high-speed connection
Microcomputer requires a NIC (network interface card)
NIC connects to a hub-like device
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Basic ConfigurationsMicrocomputer-to-
InternetVery popular with home users and some small businesses
Typically a dial-up modem is used to connect users
microcomputer to an Internet service provider.Newer technologies such as DSL and cable modems are replacing
modems.
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Basic ConfigurationsLocal Area
Network-to-Local Area Network
Found in businesses and schools that have two or more LANs and
a need for them to intercommunicate.
A bridge-like device is typically used to interconnect LANs.
Bridge-like device can filterframes
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Basic ConfigurationsPersonal AreaNetwork-to-Workstation
Interconnects wireless devices such as PDAs, laptops, and music
playback devicesUsed over a short distance such as a few meters
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Basic ConfigurationsLocal Area
Network-to-Metropolitan Area Network
Used to interconnect companies (usually local area networks) to
networks that encompass a metropolitan city
High speed networks with redundant circuits
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Basic ConfigurationsLocal AreaNetwork-to-Wide Area Network
One of the most common ways to interconnect a user on a LAN
workstation to the Internet (a wide area network).
A router is the typical device that performs LAN to WAN
connections.
Routers are more complex devices than bridges/switches
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Basic ConfigurationsSensor-to-Local
Area Network
Not all local area networks deal with microcomputer workstations.
Often found in industrial and laboratory environments.
Assembly lines and robotic controls depend heavily on sensor-
based local area networks.
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Basic ConfigurationsSatellite andMicrowave
Long distance wireless connections
Many types of applications including long distance telephone,
television, radio, long-haul data transfers, and wireless data
services.
Typically expensive services but many companies offer
competitive services and rates.
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Basic ConfigurationsMobile Telephones
Quickly expanding market across the U.S. and world.
First generation analog services and second generation PCS
services available in most areas and under many types of plans.
Third generation services beginning to appear in Europe and Asia.
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Network Architecture Models
A reference model that describes the layers of hardware and
software necessary to transmit data between two points
Reference models are necessary to increase the likelihood that
different components from different manufacturers will converse
There are two models that are required learning: The OSI Model,
and the Internet Model
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Network Architecture Models
The OSI Models seven layers
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Network Architecture Models Application layer - where the application using the network
resides. Common network applications include remote login, file
transfer, e-mail, and web page browsing.
Presentation layer - performs a series of miscellaneous functions
necessary for presenting the data package properly to the sender or
receiver.
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Network Architecture Models
Session layer - responsible for establishing sessions between
users.
Transport layer - provides an end-to-end error-free network
connection. Makes sure the data arrives at the destination exactlyas it left the source.
Network layer - responsible for creating, maintaining and ending
network connections. Transfers a data packet from node to node
within the network.
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Network Architecture Models Data link layer - responsible for taking the data and transforming
it into a frame with header, control and address information, and
error detection code.
Physical layer - handles the transmission of bits over acommunications channel. Includes voltage levels, connectors,
media choice, modulation techniques.
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Network Architecture Models
The Internet Model (DoD Model or TCP/IP Model)
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Network Architecture Models
Application layer - equivalent to the OSIs presentation and
application layers
Transport layer - performs same function as OSI transport layer
Network layer - roughly equivalent to the OSIs network layer
Interface layer - equivalent to the OSIs physical and data link
layers
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Network Models in Action
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The Internet Model in Action
Note the flow of data from user to web browser and back
At each layer, information is either added or removed, depending
on whether the data is leaving or arriving at a workstation
Adding information over pre-existing information is termedencapsulation
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