Transcript Chapter 8

Computer
Confluence 7/e
© 2006 Prentice-Hall, Inc.
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Chapter 8
Networking and Telecommunication
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Chapter 8
Objectives
 Describe the basic types of technology that make
telecommunication possible
 Describe the nature and function of local-area networks and widearea networks
 Discuss the uses and implications of email, instant messaging,
teleconferencing, and other forms of online communication
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Objectives (continued)
Explain how wireless network technology is
transforming the ways people work and communicate
Describe current and future trends in
telecommunications and networking
© 2006 Prentice-Hall, Inc.
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Arthur C. Clarke’s Magical Prophecy
Clarke’s laws
 If an elderly but distinguished scientist says
that something is possible, he is almost
certainly right, but if he says that it is
impossible he is very probably wrong
 The only way to find the limits of the possible
is to go beyond them into the impossible
 Any sufficiently advanced technology is
indistinguishable from magic
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Arthur C. Clarke’s Magical Prophecy
 Arthur C. Clarke’s most famous work was the
monumental 1968 film 2001: A Space Odyssey,
in which he collaborated with movie director
Stanley Kubrick
 Clarke’s most visionary work may be a paper
published in 1945 in which he predicted the use
of geostationary communications satellites—
satellites that match the Earth’s rotation so they
can hang in a stationary position relative to the
spinning planet below, relaying wireless
transmissions between locations on the planet
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Basic Network Anatomy
 A computer network is any system of two or
more computers that are linked together
 How is networking important?
 People share computer hardware, thus reducing
costs
 People share data and software programs, thus
increasing efficiency and production
 People work together in ways that are otherwise
difficult or impossible
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Networks Near and Far
 A local area network (LAN): computers are physically close to each other,
usually in the same building
 In a wireless network each node has a tiny radio (or, less commonly, infrared)
transmitter connected to its network port
 Sends and receives data through the air rather than through cables
 Computers are linked within a
building or cluster of buildings
 Each computer and peripheral is
an individual node on the network
 Nodes are connected by cables
which may be either twisted pair (copper wires) or coaxial cable
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 Metropolitan area network (MAN) links two or more LANs within a city
 A wide area network (WAN) extends over a long distance
 Each network site is a node on the network
 Data transmitted over common pathways called a backbone
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Basic Network Anatomy
 Communication frequently happens between LANs and WANs
 Bridges and gateways: hardware devices that can pass messages between networks
 Often translate messages so they can be understood by networks that obey
different software protocols
 Routers: hardware devices or software programs that route messages as they travel
between networks
Pretty soon you’ll have no more idea
of what computer you’re using than
you have an idea of where your
electricity comes from.
—Danny Hillis, computer designer
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Specialized Networks: From GPS to Financial Systems
 Global Positioning System (GPS)
 Specialized network developed by
U.S. Department of Defense
 Includes 24 satellites that circle the Earth
 Each satellite contains a computer, an atomic
clock, and a radio
 On the ground, a GPS receiver can use
signals broadcast by three or four visible
satellites to determine its position
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 Networks that keep our global financial systems running:
 An Automated Teller Machine (ATM): a specialized terminal linked to a bank’s
main computer through a commercial banking network
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The Network Interface
 A network interface card (NIC) permits
direct network connection:
 Adds an additional serial port to the computer
 Controls the flow of data between the computer’s RAM
and the network cable
 The most common types of networks today require some kind of Ethernet card
or port in each computer
 Ethernet is a popular networking architecture developed in 1976 at Xerox
 Most newer PCs include an Ethernet port on the main circuit board, so they don’t
require NICs to connect to Ethernet networks
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Communication á la Modem
 Modem: a hardware device that connects a
computer’s serial port to a telephone line
(for remote access)
 May be internal on the system board or external,
sitting in a box linked to a serial port
 Modem transmission speed is measured in bits per second (bps) and modems
generally transmit at 28,000 bps to 56.6K bps
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 Computers send digital signals
 The modem (modulator/demodulator) converts the digital signals to
analog so that the message can be transmitted through telephone lines
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 Broadband connection—a connection with much greater
bandwidth than modems have
 DSL uses standard phone lines and is provided by phone companies in
many areas
 Cable modems provide fast network connections through cable
television networks in many areas
 High-speed wireless connections can connect computers to networks
using radio waves rather than wires
 Satellite dishes can deliver fast computer network connections as well
as television programs
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Fiber Optic Connections
 DSL and cable modems have nowhere near the bandwidth of the fiber optic
cables that are replacing copper wires in the worldwide telephone network
 A fiber optic network can rapidly and reliably transmit masses of multimedia data at
the same time that it’s handling voice messages
NETWORKS ARE BUILT ON PHYSICAL MEDIA
Type
Uses
Maximum Operating Principal
Distance (without amplification)
Cost
Twisted pair
Small LANs
300 feet
Low
Coaxial cable
Large LANs
600–2,500 feet
Medium
Fiber optic
Network backbones; WANs
1–25 miles
High
Wireless/infrared
LANs
3–1,000 feet (line of sight)
Medium
Wireless/radio
Connecting things that move
Varies considerably
High
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Wireless Network Technology
 A lightning-fast network connection to your desktop is of little use if you’re
away from your desk most of the time; when bandwidth is less important than
mobility and portability, wireless technology can provide practical solutions
 The fastest growing wireless LAN
technology is known as Wi-Fi or 802.11b
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 Another type of wireless technology is Bluetooth
 Named for a Danish king who overcame his country’s religious differences
 Overcomes differences between mobile phones, handheld computers, and PCs, making
it possible for all of these devices to communicate with each other regardless of
operating system
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 With Bluetooth it’s possible to create a
personal area network (PAN)—a network that
links a variety of personal electronic devices so they can
communicate with each other
 Bluetooth technology is currently limited to simple device
connectivity, but in the future it will open up all kinds of
possibilities:
 A pacemaker senses a heart attack and notifies the victim’s
mobile phone to dial 911
 A car radio communicates with parking-lot video cameras
to find out where spaces are available
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 A pen scans business cards and sends the information to a PDA inside a
briefcase
 A medical wristband transmits an accident victim’s vital information to a
doctor’s handheld computer
 A cell phone tells you about specials on clothes that are available in your
size as you walk past stores in a mall
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Communication Software
 Protocol is a set of rules for the exchange of data between a terminal and a
computer or between two computers
 Communication software establishes a protocol that is followed by the
computer’s hardware
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 Many forms:
 Network operating system (NOS)
 Handles communications between many workstations
 Client/server model
 One or more computers act as dedicated servers and all the
remaining computers act as clients
 Peer-to-peer model
 Every computer on the network is both client and server
 Many networks are hybrids, using features of the
client/server and peer-to-peer models
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The Network Advantage
 Why do people use networks?
 To share computer resources
(hardware and software)
 To support working together in new
and different ways
 Microsoft Exchange, the most widely-used groupware
product, combines email, scheduling, contacts, tasks, and
other personal information management features to facilitate
information sharing and workgroup collaboration
 Exchange Server is the server end of a client/server solution
that also includes Microsoft Outlook or its Web-based
equivalent, Outlook Web Access (OWA), which is shown
here
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A Home Computer Network
Wireless access
point
DSL Modem
Wireless laptop
Firewall/router
USB Cable
Multiplayer Games
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Email, Instant Messaging, and Teleconferencing:
Interpersonal Computing
The Many Faces of Email
 Email system enables you to send and receive messages to others on the
network
 Web-based email systems and many older UNIX-based programs require that
read and unread messages be stored in post office boxes or folders on the
remote mail servers
 Many email messages are plain ASCII text
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 Even if their software can display HTML mail, not all email users want HTML
emails
HTML encoding can slow down an email program
An HTML email message can also carry a Web bug
 Most email programs can send and receive formatted word processor
documents, pictures, and other multimedia files as attachments to messages
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Mailing Lists
 Mailing lists enable you to participate in email discussion groups on specialinterest topics
 Subscribing to a busy list might mean receiving hundreds of messages each
day
 To avoid being overwhelmed by incoming mail, many list members sign up to
receive them in daily digest form
 Some lists are moderated to ensure that the quality of the discussion remains high
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Network News
 Newsgroup: a public discussion on a particular subject
 Notes written to a central Internet site
 Redistributed through a worldwide newsgroup network called USENET
 Listserv mail messages are delivered automatically to your mailbox, but you have
to seek out information in newsgroups
 Mailing list messages are sent to a specific group of people, whereas newsgroup
messages are available for anyone to see
 Moderated newsgroups contain only messages that have been filtered by
designated moderators
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Rules of Thumb: Online Survival Tips
 If you don’t have to be on line, go off line
 Avoid peak hours
 Let your system do as much of the work as possible
 Store names and addresses in an on-line address book
 Protect your privacy
 Cross-check on-line information sources
 Be aware and awake
 Avoid information overload
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Instant Messaging and Teleconferencing:
Real-Time Communication
 Mailing lists and newsgroups are delayed or asynchronous communication
The sender and the recipients don’t have to be logged in at the same time
 Instant messaging (IM) has been possible since the days of text-only
Internet access
 Newer, easier to use messaging systems from AOL, Microsoft, Yahoo,
Apple, and others have turned instant messaging into one of the most
popular Internet activities
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 Online services also offer chat rooms—public or private virtual conference
rooms where people with similar interests or motivations can type messages
to each other and receive near instant responses
 Several IM programs make it possible to carry on two-way video
teleconferences
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Computer Telephony
 Voice mail: a messaging system with the ability to store, organize, and forward
messages
 An example of a growing trend toward computer telephony integration (CTI)—the
linking of computers and telephones to gain productivity
 It’s also possible to send voice signals through a LAN, a WAN, or the Internet,
bypassing the phone companies (and their charges) altogether
 Handheld PDA computers use software to integrate the functions of a PDA, a
phone, and an Internet terminal
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 Online communication enables decisions to evolve over time
 Online communication makes long-distance meetings possible
 Email and instant messaging emphasize the message over the messenger
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Email, Instant Messaging, and Teleconferencing:
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Online Issues: Reliability, Security, Privacy, and Humanity
 Email and teleconferencing are vulnerable to machine failures, network
glitches, human errors, and security breaches
 Email can be overwhelming
 Email can be unsolicited
 Email can pose a threat to privacy
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 Email can be faked
 Email works only if everybody plays
 Email and instant messaging filter
out many “human” components of
communication
 Problems notwithstanding, email and electronic
messaging have become fixtures in businesses,
schools, and government offices everywhere
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Digital Communication in Perspective
 Many services we take for granted today—video rentals, cable TV,
newspapers, and magazines, for example—will be transformed or
replaced by digital high-bandwidth interactive delivery systems of the
future
 At the same time, entirely new forms of communication are likely to
emerge
 Telecommunications technology is rapidly changing our lives, and the
changes will accelerate as the technology improves
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Rules of Thumb: Netiquette
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
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
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
Say what you mean, say it with care and keep it short
Proofread your messages
Don’t assume you’re anonymous
Learn the “nonverbal” language of the Net
Keep your cool
Don’t be a source of spam
Send no-frills mail
Check your FAQs
Give something back
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Inventing the Future: A World Without Wires
 Most of us connect to the Internet through wires
 Wi-Fi, or 802.11b, a wireless multiband LAN technology
 Built on Ethernet’s data packets and Internet protocols
 Turning up in home networks, public buildings, and neighborhood freenets
 Several other promising technologies are being tested and refined in research
labs




Ultrawideband
Mesh networks
Adaptive radio
Software-defined radio
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Inventing the Future: A World Without Wires
We stand at the brink of a transformation. It is
a moment that echoes the birth of the Internet
in the mid-’70s…This time it is not wires but the
air between them that is being transformed.
— Chris Anderson, Editor in Chief, Wired
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Lesson Summary
 Networking is one of the most important trends in computing today
 LANs are made up of computers that are close enough to be directly
connected with cables or wireless radio transmitters/receivers
 Most LANs include shared printers and file servers
 WANs are made up of computers separated by considerable distance
 Many computer networks are connected together through the Internet so
messages and data can pass back and forth among them
 Some specialized networks, including global positioning systems and
financial systems serve unique functions
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Lesson Summary (continued)
 Most computer networks today use the Ethernet architecture; an Ethernet
port is a standard feature on most modern PCs
 Communication software takes care of the details of communication
between machines—details like protocols that determine how signals will
be sent and received
 Email, instant messaging, and teleconferencing are the most common
forms of communication between people on computer networks
 It’s not clear how all of these emerging technologies will converge; what is
clear is that the wireless revolution is far from over
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