Transcript Business Data Communications and Networking

Business Data
Communications and
Networking, 6th ed.
FitzGerald and Dennis
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Copyright © 1999 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this work
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herein.
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Chapter 1
Introduction to Data
Communications
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Objectives
Become familiar with…
 the history of communications and
information systems,
 the applications of data communication
networks,
 the major components of networks,
 the importance of standards,
 three key trends in communications and
networking,
Understand the role of network layers.
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INTRODUCTION
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Why Study Data
Communications?
The key technology of the information age is
communications.
Data communications and networking is a
truly global area of study, both because the
technology enables global communication,
and because new technologies and
applications often emerge from a variety of
countries and spread rapidly around the
world.
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DATA COMMUNICATIONS
NETWORKS
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Data Communications
 Data
Communications
The movement of computer information from one
point to another by means of electrical or
optical transmission systems.
Such systems are often called data
communications networks.
 Telecommunications
Includes the transmission of voice and video as
well as data.
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Analog and Digital Data
Transmission
 Digital
Signals are
electrical pulses
generated by a computer
or a terminal (binary: onoff)
 Analog
signals are
audio tones into which the
digital signals are
converted for transmission
in a telephone network
(wave: numerous values)
©Jaana Porra 2001
 A modem is a device
which converts the direct
electrical signals produced
by the computer (positive
and negative voltages of
electricity) to modulated
audio signals that can be
sent over telephone
communications circuits
 Connector
cable
connects the modem to
the micro computer (or a
terminal)
Using Telephone Networks (Analog)
for Data Communications (Digital)

Local loop: In a telephone

network, the “last mile” which
connects home or office to
telephone company’s central
office

Central Office, end office
or Exchange office contains
the switching facilities operated
by the telephone company.

Private Leased Circuit
refers leasing a private circuit
path and bypassing switching at
the central office
©Jaana Porra 2001
Interchange
Channels/Circuits (IXC) are
the circuits that go from one
telephone company central
office to another central office
(coaxial, fiber, satellite etc.)

Common Carrier is a
company recognized by FCC or
an appropriate state licensing
agency as having the right to
furnish telecommunications
services to individual
subscribers or business
organizations
Components of a Network
 Server
(or Host computer)
Central computer in the network, storing data or
software that can be accessed by the clients.
 Client
The input/output hardware device at the other
end of a communications circuit.
 Circuit
The pathway through which the messages travel.
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Components of a Network
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Computer Networks
in a Nutshell
Corporation 1, Town 1
Corporation 2, Town 2
M
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T
WIDE
R
O
AREA
P
O
NETWORK
L
BACKBONE
B
LAN LAN A
I
LAN
C
T
K
A
N
BACKBONE B
O AREA
N NW
©Jaana Porra 2001
BACKBONE E
BACKBONE
B
A
C BACKBONE
K
B
O
N BACKBONE
E
Intranet, Internet, Extranet in a
Nutshell
©Jaana Porra 2001
INTRANET
I
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T
R
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INTRANET A
X
N
E E
INTRANET T
INTRANET
INTERNET
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T
E T EXTRANET
Types of Networks
Networks can be classified in many different
ways. One of the most common is by
geographic scope:
•
•
•
•
Local Area Networks (LAN)
Backbone Networks (BNs)
Metropolitan Area Networks (MANs)
Wide Area Networks (WANs)
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Types of Networks
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Types of Networks
 Local Area
Networks (LAN)
A group of microcomputers of terminals located
in the same general area and connected by a
common circuit.
Covers a clearly defined small area, such as
within or between a few buildings,
Support data rates of 10 to 100 million bits per
second (Mbps).
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Types of Networks
 Backbone
Network (BN)
A larger, central network connecting several
LANs, other BNs, metropolitan area networks,
and wide area networks.
Typically span up to several miles.
Support data rates from 64 Kbps to 45 Mbps.
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Types of Networks
 Metropolitan Area
Network (MAN)
Connects LANs and BNs located in different
areas to each other and to wide area networks.
Typically span from 3 - 30 miles.
Supports data rates of 100 to 1000 Mbps.
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Types of Networks
 Wide Area
Network (WAN)
Connects BNs and MANs and are usually leased
from inter-exchange carriers.
Typically span hundreds or thousands of miles.
Supports data rates of 28.8 Kbps to 2 Gbps.
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Some Network Architectures
 Peer-to-Peer
network

is a computer network in
which computers function
as equals
 Hierarchical
Network is
a computer network which
is controlled by a central
computer often called the
host computer
©Jaana Porra 2001
Point-to-point network
connects two points (e.g.,
a micro computer to a
server)

Broadcast network
(one-to-many) connects
one point (e.g., a server)
to many (e.g., a host
computer to micro
computers)
Connecting Network Nodes

Circuit is the pathway through

which the messages travel
(copper wire, fiber optic cable,
wireless transmission)


connects two similar networks
which have the same network
protocol. It also chooses the
best route between two
networks when there are
multiple paths between them.
Bridge is a device that
connects two similar networks
using the same data link and
network protocols.

©Jaana Porra 2001
Brouter is a device which
combines the functions of a
bridge and a router.
Gateway is a device that
connects two dissimilar
networks and allows two
networks of different vendors to
communicate by translating one
vendor’s protocol into another.
Router is a device that

Repeater is a device used to
boost the strength of a signal.
Repeaters are spaced at
intervals throughout the length
of a communication circuit.
Establishing a Connection

Protocol is a formal set of
conventions governing the
format and control of inputs and
outputs between two
communications devices. This
includes the rules by which
these two devices communicate
as well as handshaking and line
discipline

Handshaking is the
exchange of predetermined
signals when a connection is
established between two data
devices. This is used to
establish the circuit and
message path.
©Jaana Porra 2001

Session is the logical
connection between two
terminals. This is the part of the
message transmission between
two points after the
communications circuit has
been established and is
functioning.
Client-Server in a Nutshell
2. Distributed
Presentation
Management
Dialog
Application
or
Presentation
Manager
1. Fill-in-the
Blanks
User Interface
4. Distributed
Data Access
6. Local
Processing
Data Base
Data
Man.
Files
SQL
Flat File
5. Physical
3. Application
File Server
to Application
©Jaana Porra 2001
Interface
NETWORK MODEL
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Network Model
A method of describing and analyzing data
communications networks, by breaking the
entire set of communications functions into
a series of layers, each of which can be
defined separately.
This allows vendors to develop software and
hardware to provide the functions
separately.
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Networking Model
Open System Interconnection (OSI) Model,
developed in 1984, helped change the face
of network computing.
Other models like TCP/IP have become more
prominent in the design of networks and
network technology.
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International Organization for
Standardization (ISO) Open Systems
Interconnection (OSI) Reference Model
APPLICATION
PRESENTATION
SESSION
Application Services APPLICATION
are Provided by the
PRESENTATION
Upper Layer
Infrastructure
SESSION
TRANSPORT
DATA LINK
End-to-End Services
are Provided by the
Lower Layer
Infrastructure
PHYSICAL
©Jaana Porra 2001
PHYSICAL
TRANSPORT
NETWORK
NETWORK
DATA LINK
The OSI Reference Model
Continued
©Jaana Porra 2001
APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
Manages the communication A letter mailed
between applications
and received
Adds structure to the
The envelope layout
exchanged data units
Adds control mechanisms Address, return address
to exchanged data
postage on envelope
Transfers and multiplexes data The US Postal
reliably across the network
Service
Transfers data over the network The Postal Service ground
independent of media and
and air transportation
topology of subnetworks
network
Transfers data over a single
A mail truck from post
communications link, does
office to airport
framing and error control
Responsible for the electro-mechanical The truck
interface to the communications media
A 4-Layer Model
©Jaana Porra 2001
APPLICATION
NETWORK
DATA LINK
Application software
used by the network
APPLICATION
user
Translates and routes the
message; collects
NETWORK
accounting information
Controls the physical
layer; formats the message DATA LINK
detects and corrects errors
PHYSICAL
PHYSICAL
The physical connection
between sender and
receiver
Networking Model
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Simplified Network Model
 Application
layer (Layer 4)
The application software used by the network
user, allows the user to define what message
are sent over the network.
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Simplified Network Model
 Network
layer (Layer 3)
Takes the message generated by the application
layer and performs three functions before
passing them to the data link layer.
1. Translates the destination of the message into an
address understood by the network.
2. If multiple routes possible, it decides which routes
to take.
3. Collects message accounting information that can
be used to identify how many messages each user
has sent and to track errors.
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Simplified Network Model
 Data
link layer (Layer 2)
Takes the message generated by the network
layer and performs three functions before
passing the message on the physical layer.
1. It controls the physical layer by deciding when to
transmit messages over the media.
2. It formats the message by indicating where
messages start and end, and which part is the
address. (It may break it into smaller packets).
3. It detects and corrects any errors that have
occurred in the transmission of the message.
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Simplified Network Model
 Physical
layer (Layer 1)
The physical connection between the sender
and receiver.
It transfers a series of electrical, radio, or light
signals through the circuit from sender to
receiver.
It specifies the type of connection, and the
signals that pass through it.
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Network Models
For Communications to be successful, each
layer in one computer must be able to
communicate with its matching layer in the
other computer.
This is accomplished by standards.
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NETWORK STANDARDS
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The Importance of Standards
Standards are necessary in almost every
business and public service entity.
The primary reason for standards is to ensure
that hardware and software produced by
different vendors can work together.
The use of standards makes it much easier to
develop software and hardware that link
different networks because software and
hardware can be developed one layer at a
time.
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The Standards Making
Process
Two types of standards:
• Formal standards are developed by an official
industry or government body.
• Defacto standards emerge in the marketplace
and supported by several vendors, but have no
official standing.
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The Standards Making
Process
Formal standardization process has three stages
1. Specification stage: developing a
nomenclature and identifying the problems to
be addressed.
2. Identification of choices stage: those working
on the standard identify the various solutions
and choose the optimum solution from among
the alternatives.
3. Acceptance, the most difficult stage: defining
the solution and getting recognized industry
leaders to agree on a single, uniform solution
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Telecommunications
Standards Organizations
 International
Organization for Standards
(ISO)
Member of the ITU, makes technical
recommendations about data communications
interfaces.
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Telecommunications
Standards Organizations
 International
Telecommunications Union Telecommunication Standardization Sector
(ITU-TSS)
Technical standard setting organization of the UN
ITU. Formerly called the Consultative
Committee on International Telegraph and
Telephone (CCITT)
Comprised of representatives of over 150 Postal
Telephone and Telegraphs (PTTs), like AT&T,
RBOCs, or common carriers.
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TC Standards Organizations
• American National Standards Institute (ANSI)
• Institute of Electrical and Electronics Engineers
(IEEE)
• Electronic Industries Association (EIA)
• National Institute of Standards and Technology
(NIST)
• National Exchange Carriers Association (NECA)
• Corporation for Open Systems (COS)
• Electronic Data Interchange -(EDI) of Electronic
Data Interchange for Administration Commerce
and Transport (EDIFACT).
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FUTURE TRENDS IN
COMMUNICATIONS AND
NETWORKING
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Future Trends
Between now and the year 2010, data
communications will grow faster and
become more important than computer
processing itself.
There are three major trends driving the
future of communications and networking:
• Pervasive Networking
• The Integration of Voice, Video and Data
• New Information Services
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Pervasive Networking
In the future, communications networks will
be everywhere.
This pervasive networking means that
virtually any computer will be able to
communicate with any other computer in
the world.
This will increase telecommuting in which
employees perform some or all of their work
at home instead of going to the office each
day.
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Pervasive Networking
Cellular telephone networks will begin to
compete directly with the current wired
telephone network.
Pervasive networking will also increase the
use of electronic data interchange (EDI),
the paperless transmission of business
documents between companies.
The Internet has experienced such rapid
growth that it now connects millions of
computers in virtually every country in the
world.
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The Integration of Voice,
Video and Data
The integration of voice and data is largely
complete in wide area networks.
The integration of video into computer
networks has been much slower, partly due
to past legal restrictions, and partly due to
the immense communications needs of
video.
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New Information Services
The World Wide Web has changed the nature
of computing so now that almost anyone
with a computer can be their own publisher.
Never before in the history of the human race
has so much knowledge and information
been available to ordinary citizens.
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End of Chapter 1
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End of Lecture 2!
© 2001 Jaana Porra University of Houston