Transcript Computer Confluence 6/e

© 2008 Prentice-Hall, Inc.
Slide 1
Chapter 8
Networking and Digital Communication
© 2008 Prentice-Hall, Inc.
Slide 2
 Describe the basic types of technology that make
telecommunication possible.
 Describe the nature and function of local area networks and
wide area networks.
 Discuss the uses and implications of email, instant
messaging, blogging, teleconferencing, and other forms of
online communication.
© 2008 Prentice-Hall, Inc.
Slide 3
 Explain how wireless network technology is
transforming the ways people work and communicate.
 Describe current and future trends in
telecommunications and networking.
© 2008 Prentice-Hall, Inc.
Slide 4
 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.
© 2008 Prentice-Hall, Inc.
Slide 5
 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.
© 2008 Prentice-Hall, Inc.
Slide 6
 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.
© 2008 Prentice-Hall, Inc.
Slide 7
Networks Near and Far
 In a local area network (LAN) computers are physically close to each other,
usually in the same building.

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.
 In a wireless network each node has a tiny radio (or, less commonly, infrared)
transmitter connected to its network port.

Computers send and receive data through the air rather than through cables.
© 2008 Prentice-Hall, Inc.
Slide 8
 A metropolitan area network (MAN) links two or more LANs within a city.
 A wide area network (WAN) extends over a long distance.

Each networked LAN site is a node on the WAN.
 Data transmitted over common pathways called a backbone.
© 2008 Prentice-Hall, Inc.
Slide 9
 Communication frequently happens between LANs and
WANs

Routers: hardware devices or software programs that route
messages as they travel between networks
 Mesh networks: an alternative to today’s networks; rely on
centralized routers


Used to set up small, temporary communication systems
Example: emergency personnel use at fire scenes to coordinate
actions
“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
© 2008 Prentice-Hall, Inc.
Slide 10
Specialized Networks: From GPS to Financial Systems
 Global Positioning System (GPS)

GPS is a specialized network developed by
U.S. Department of Defense.
 It 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.
© 2008 Prentice-Hall, Inc.
Slide 11
 Networks that keep our global financial systems running:

Automated Teller Machine (ATM): a specialized terminal linked to a bank’s main
computer through a commercial banking network
© 2008 Prentice-Hall, Inc.
Slide 12
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.
© 2008 Prentice-Hall, Inc.
Slide 13
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 measured in bits per second (bps)
 Transmit at 28,000 bps to 56.6K bps
© 2008 Prentice-Hall, Inc.
Slide 14
 Computers send digital signals.
 The modem (modulator/demodulator) converts the digital signals to
analog so that the message can be transmitted through telephone lines and
converts it back on the other end.
© 2008 Prentice-Hall, Inc.
Slide 15
 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.
© 2008 Prentice-Hall, Inc.
Slide 16
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.
© 2008 Prentice-Hall, Inc.
Slide 17
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.
© 2008 Prentice-Hall, Inc.
Slide 18
 Bluetooth: another type of wireless technology
 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
© 2008 Prentice-Hall, Inc.
Slide 19
 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.
© 2008 Prentice-Hall, Inc.
Slide 20
 More examples of Bluetooth possibilities:
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.
© 2008 Prentice-Hall, Inc.
Slide 21
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.
© 2008 Prentice-Hall, Inc.
Slide 22
 Communication software takes many forms:
 Network operating system (NOS)
 System handles communications among 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.
© 2008 Prentice-Hall, Inc.
Slide 23
The Network Advantage
Why do people use networks?
 Networks enable people to share computer hardware resources, reducing
costs and enabling people to take advantage of powerful computer
equipment.
 Networks enable people to share data and software programs, increasing
efficiency and productivity.
 Networks enable people to work together or collaborate in ways that are
difficult or impossible without network technology.
© 2008 Prentice-Hall, Inc.
Slide 24
A Home Computer Network
Wireless access
point
DSL modem
Wireless laptop
Firewall/router
USB cable
Multiplayer games
© 2008 Prentice-Hall, Inc.
Slide 25
The Many Faces of Email
 Email systems enable 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.
© 2008 Prentice-Hall, Inc.
Slide 26
 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.
© 2008 Prentice-Hall, Inc.
Slide 27
Mailing Lists
 Mailing lists enable you to participate in email discussion groups on
special-interest 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.
© 2008 Prentice-Hall, Inc.
Slide 28
Newsgroups
 Newsgroup: a public discussion on a particular subject
 Notes are written to a central Internet site.
 Notes are 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.
© 2008 Prentice-Hall, Inc.
Slide 29
Rules of Thumb: Online Survival Tips
 Let your system do as much of the work as possible.
 Store names and addresses in computer-accessible
addressbook.
 Don’t share your email address.
 Don’t open suspicious attachments.
 Protect your privacy.
 Cross-check on-line information sources.
 Be aware and awake.
 Avoid information overload.
© 2008 Prentice-Hall, Inc.
Slide 30
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.
© 2008 Prentice-Hall, Inc.
Slide 31
 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.
© 2008 Prentice-Hall, Inc.
Slide 32
Computer Telephony
 Voice mail is a messaging system with the ability to store, organize, and
forward messages.
 An example of a growing trend toward computer telephony integration
(CTI) is 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.
© 2008 Prentice-Hall, Inc.
Slide 33
Computer Telephony
 Internet Telephony has become a legitimate competitor to traditional
phone companies.
 Voice over IP (VoIP) requires a broadband connection to carry your
call over the Internet.
 You can place a calling using either a traditional phone with an adapter
or an Internet-connected PC with a microphone headset and
appropriate software.
© 2008 Prentice-Hall, Inc.
Slide 34
Computer Telephony
 Advantages of VoIP
 Calls are less expensive if you already have a broadband connection.
 Calls are routed to you no matter where you are connected.
 VoIP phones integrate more easily with online address books, video
conference services, and other Internet services.
© 2008 Prentice-Hall, Inc.
Slide 35
Computer Telephony
 Disadvantages of VoIP
 Communication is impossible during a power outage (most networks
are unusable).
 There is no 911 or directory assistance service available.
 Quality is suspect because there is no guarantee of packets being
delivered in a timely manner.
© 2008 Prentice-Hall, Inc.
Slide 36
Social Networks and Information Sharing
 Online communities such as MySpace and Facebook
 Massively multiplayer role playing games (MMORPG)
 Common information resources such as Flickr and Wikipedia
© 2008 Prentice-Hall, Inc.
Slide 37
Email Issues
 Problems with Spam – more than 50% of e-mails are unsolicited.
 Email and teleconferencing are vulnerable to machine failures, network
glitches, human errors, and security breaches.
 Email can be overwhelming.
 Email can pose a threat to privacy.
© 2008 Prentice-Hall, Inc.
Slide 38
Don’t Get Hooked—Advice on Phishing
Examine the URL in the address bar.
Re-examine the URL in the address bar.
Look for the https prefix.
Look for the padlock icon.
Pay attention to pop-up warnings about fraudulent certificates.
Make your own Web connection.
© 2008 Prentice-Hall, Inc.
Slide 39





Cookies – Can be used by snoopers to get information about you
Wireless issues of access, security, and privacy
Perils of posting too much information on blogs and websites
Internet Addiction – Some game players spend 40-80 hrs a week online
Virtual Sweatshops
© 2008 Prentice-Hall, Inc.
Slide 40
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.
© 2008 Prentice-Hall, Inc.
Slide 41
 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.
© 2008 Prentice-Hall, Inc.
Slide 42
 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.
© 2008 Prentice-Hall, Inc.
Slide 43