Chapter 1

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1

Chapter One

Introduction to Computer
Networks and Data
Communications

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Introduction


Who today has
not

used a computer network?


Mass transit, interstate highways, 24
-
hour bankers,
grocery stores, cable television, cellphones,
businesses and schools, and retail outlets support
some form of computer network

Chapter One
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Introduction to Computer

Networks And Data Communications

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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 areas


Local area network


networks that are small in
geographic size spanning a room, floor, building, or
campus

Chapter One
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Introduction to Computer

Networks And Data Communications

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The Language of Computer Networks


Metropolitan area network


networks that serve an
area of 1 to 30 miles, approximately the size of a
typical city


Wide area network


a large network that
encompasses parts of states, multiple states, countries,
and the world

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Introduction to Computer

Networks And Data Communications

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The Language of Computer Networks


Personal area network


a network of a few meters,
between wireless devices such as PDAs, laptops, and
similar devices


Voice network


a network that transmits telephone
signals


Data network


a network that transmits computer
data

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Introduction to Computer

Networks And Data Communications

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The Language of Computer Networks


Data communications


the transfer of digital or
analog data using digital or analog signals


Telecommunications


the study of telephones and
the systems that transmit telephone signals


Network management


the design, installation, and
support of a network, including its hardware and
software

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Introduction to Computer

Networks And Data Communications

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The Big Picture


Networks are composed of many devices, including:


Workstations (computers, telephones)


Servers


Network hubs and switches (bridges)


Routers (LAN to WAN and WAN to WAN)


Telephone switching gear

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Computer Networks


Basic Connections


Computer terminal / microcomputer to mainframe


Microcomputer to local area network


Microcomputer to Internet


Local area network to local area network


Personal area network to workstation

Chapter One
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Introduction to Computer

Networks And Data Communications

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Computer Networks


Basic Connections


Local area network to metropolitan area network


Local area network to wide area network


Sensor to local area network


Satellite and microwave


Wireless telephone and wired telephone to network

Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Computer Terminal /
Microcomputer to Mainframe Computer


Predominant form in the 1960s and 1970s


Still used in many types of businesses for data entry
and data retrieval


Usually involves a low
-
speed connection

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Microcomputer to
Local Area Network


Highly common throughout business and academic
environments, and now homes


Typically a medium
-

to high
-
speed connection


Computer (device) requires a NIC (network interface
card)


NIC connects to a hub
-
like device

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Microcomputer to
Internet


Popular with home users and small businesses


Often a dial
-
up modem is used to connect user’s
microcomputer to an Internet service provider


Technologies such as DSL and cable modems are
replacing modems

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Local Area Network
to Local Area Network


Found in systems that have two or more LANs and a
need for them to intercommunicate


A bridge
-
like device (such as a switch) is typically
used to interconnect LANs


Switch can
filter

frames

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Personal Area
Network to Workstation


Interconnects wireless devices such as PDAs, laptops
and notebooks, and music playback devices


Used over short distances such as a few meters

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Local Area Network
to Metropolitan Area Network


Used to interconnect companies (usually their local
area networks) to networks that encompass a city


High
-
speed networks with redundant circuits


Metro Ethernet is latest form of metropolitan LAN


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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


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 switches


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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Wide Area Network
to Wide Area Network


High
-
speed routers and switches are used to connect
one wide area network to another


Thousands of wide area networks across North
America, many interconnected via these routers and
switches


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Introduction to Computer

Networks And Data Communications

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Basic Connections


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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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Satellite and
Microwave


Typically 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


Newer shorter
-
distance services such as Wi
-
Max


Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Basic Connections


Wireless or Cellular
Telephones


Constantly expanding market across the U.S. and
world


Third generation services available in many areas and
under many types of plans


Newest generation includes higher speed data
transfers (100s of kilobits per second)


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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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An Additional Basic Connection


Telephone to Network


Telephone systems are ubiquitous and now carry
more data than voice


Common configuration


telephone connected to
POTS


Newer configuration (VoIP)


telephone to LAN via
gateway or telephone to gateway via DSL/cable


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures


A reference model that describes the layers of
hardware and software necessary to transmit data
between two points or for multiple devices /
applications to interoperate


Reference models are necessary to increase likelihood
that different components from different
manufacturers will converse


Two models to learn: OSI model and TCP/IP protocol
suite


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures


The OSI model’s seven layers:


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures
-

OSI


Application layer


where the application using the
network resides. Common network applications
include web browsing, e
-
mail, file transfers, and
remote logins


Presentation layer


performs a series of
miscellaneous functions necessary for presenting the
data package properly to the sender or receiver


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures
-

OSI


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 exactly as 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.


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures
-

OSI


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
a communications channel. Includes voltage levels,
connectors, media choice, modulation techniques


Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures


The TCP/IP protocol suite (DoD protocol suite, Internet
model):


Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures


TCP/IP


Application layer


equivalent to OSI’s application
and presentation layers


Transport layer


equivalent to OSI’s transport layer


Network (Internet or internetwork) layer


equivalent
to OSI’s network layer


Network access (data link/physical) layer


equivalent to OSI’s data link and physical layers

Chapter One
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Introduction to Computer

Networks And Data Communications

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Network Architectures


Logical and physical connections


A logical
connection is one that exists only in the software,
while a physical connection is one that exists in the
hardware


Note that in a network architecture, only the lowest
layer contains the physical connection, while are
higher layers contain logical connections

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
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Introduction to Computer

Networks And Data Communications


Logical and physical connections

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Chapter One
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Introduction to Computer

Networks And Data Communications


Example of data flow through layers

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Chapter One
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Introduction to Computer

Networks And Data Communications


Network connections in action

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The TCP/IP protocol suite 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


The adding of information over pre
-
existing
information is termed
encapsulation

Chapter One
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Introduction to Computer

Networks And Data Communications

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Chapter One
-

Introduction to Computer

Networks And Data Communications