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Chapter 1
The Big Picture
Introduction to Computer Networks and Data
Communications
Data Communications & Computer
Networks, Second Edition
1
Introduction
Who today has not used a computer
network?
 Examples?
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Networks, Second Edition
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The Language of Computer
Networks
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Computer network
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Local area network
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Metropolitan area network
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Networks, Second Edition
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The Language of Computer
Networks
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Wide area network
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Personal area network
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Data communications
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Networks, Second Edition
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The Language of Computer
Networks
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Voice network
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Data network
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Telecommunications
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Network management
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Networks, Second Edition
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The Big Picture of Networks
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Networks are composed of many devices,
including:
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workstations (computers and telephones)
network servers
network hubs and switches (bridges)
routers (LAN-WAN and WAN-WAN)
telephone switching gear
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Networks, Second Edition
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Data Communications & Computer
Networks, Second Edition
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Computer Networks - Basic
Configurations
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Computer terminal-to-mainframe computer
Microcomputer-to-mainframe computer
Microcomputer-to-local area network
Microcomputer-to-Internet
Local area network-to-local area network
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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Networks, Second Edition
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Computer 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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Networks, Second Edition
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Data Communications & Computer
Networks, Second Edition
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Microcomputer-to-Local Area
Network
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Highly 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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Networks, Second Edition
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Networks, Second Edition
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Microcomputer-to-Internet
Very popular with home users and some
small businesses
 Typically a dial-up modem is used to
connect user’s microcomputer to an
Internet service provider.
 Newer technologies such as DSL (digital
subscriber line) and cable modems are
replacing dial-up modems.
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Networks, Second Edition
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Networks, Second Edition
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Local 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 filter traffic
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Networks, Second Edition
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Networks, Second Edition
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Personal Area Network-toWorkstation
Interconnects devices such as PDAs,
laptops, and music playback devices using
wired or wireless transmission
 Used over a short distance such as a few
meters
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Networks, Second Edition
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Networks, Second Edition
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Local 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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Networks, Second Edition
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Data Communications & Computer
Networks, Second Edition
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Local Area Network-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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Networks, Second Edition
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Data Communications & Computer
Networks, Second Edition
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Sensor-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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Networks, Second Edition
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Networks, Second Edition
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Satellite and Microwave
Long distance wireless connections.
 Many types of applications including long
distance telephone, television, radio, longhaul data transfers, and wireless data
services.
 Typically expensive services but many
companies offer competitive services and
rates.
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Networks, Second Edition
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Networks, Second Edition
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Network Architecture Models
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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 converge.
There are two models that are required learning:
The OSI Model, and the Internet Model.
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Networks, Second Edition
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OSI Model
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Seven layers
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Networks, Second Edition
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OSI Seven Layers
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Application layer
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Presentation layer
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performs a series of miscellaneous functions necessary for
presenting the data package properly to the sender or receiver.
Session layer
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where the application using the network resides. Common network
applications include remote login, file transfer, e-mail, and web page
browsing.
responsible for establishing sessions between users.
Transport layer
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provides an end-to-end error-free network connection. Makes sure
the data arrives at the destination exactly as it left the source.
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Networks, Second Edition
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OSI Seven Layers
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Network layer
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Data link layer
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responsible for creating, maintaining and ending network
connections. Transfers a data packet from node to node within the
network
responsible for taking the data and transforming it into a frame with
header, control and address information, and error detection code.
Physical layer
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handles the transmission of bits over a communications channel.
Includes voltage levels, connectors, media choice, modulation
techniques.
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Networks, Second Edition
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The Internet Model (TCP/IP Model)
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Networks, Second Edition
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OSI Model vs. Internet Model
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Application layer - equivalent to the OSI’s
presentation and application layers
Transport layer - performs same function as OSI
transport layer
Network layer - roughly equivalent to the OSI’s
network layer
Interface layer - equivalent to the OSI’s physical
and data link layers
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Networks, Second Edition
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Logical and physical connections
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Logical and physical
connections.
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Note that in a network
architecture model, only the
lowest layer contains a
physical connection, while all
higher layers contain logical
connections
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Networks, Second Edition
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Network Models in Action
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The Internet Model in Action
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See Figure 1-19 on pp. 25
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 termed encapsulation
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Networks, Second Edition
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Networks, Second Edition
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