Transcript Chapter 1

Chapter 1:
First Things First
Web 101
Third Edition
Created by Wendy G. Lehnert &
Richard L. Kopec
Modified by Linda Kenney
January 22, 2008
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Learning Objectives
• Understand the purpose of your computer’s
CPU, RAM, and secondary storage.
• Learn about bits, bytes, kilobytes, megabytes,
and gigabytes.
• Find out how the Internet is structured and how
computers become part of the Internet.
• Discover how IP and DNS addresses are used.
• Master the basic navigational features of your
Web browser.
1-2
Taking Charge
• The Internet (or Net) is used by students and
others for many purposes.
• What are some purposes?
1-3
Organization of a Computer System
Central
Processing
Unit
Input
Device
Main
Memory
Output
Device
Secondary
Storage
1-4
The CPU (Central Processing Unit)
• Fetches instructions from main memory
• Carries out the operations commanded by the
instructions
• Each instruction produces some outcome
1-5
Memory and Storage
• Random Access Memory (RAM)
– This is also called Main Memory
• Long-term storage
1-6
Main Memory (or Primary Storage)
• Random Access Memory (RAM)
• The memory that the CPU uses when it
executes instructions
• The CPU reads and writes to RAM very quickly
• RAM is volatile - the information goes away
when the computer is turned off or restarted
(short-term)
• Each program that you run requires some
amount of RAM
1-7
Secondary Storage
• A nonvolatile (or “permanent”) storage medium
• Contents retained while power is off
• Hard disk drives are most common
– Records data magnetically on a circular disk
– Provides fast access to large amounts of data
• Optical devices store data on CD’s as pits
• USB flash memory devices
– High capacity device plugs into USB port
– Portable, reliable, and fits easily in a pocket
1-8
Software
• The programs that run on a computer
• Two major categories
– Operating systems
• Controls the processes within the computer
• Manages the computer's hardware devices
– Application Software
• Solve problems or perform tasks needed by users
• Examples include word processing, spreadsheets, games,
Internet browsers, playing music, etc)
• Each program is referred to as an application
1-9
Units of Memory
• The size of files is measurable.
• The smallest unit of data is the bit.
– A bit is either a 1 or a 0
– All data (and files) are a pattern of bits
• A byte is 8 bits
– Each byte can represent a character (letter, number
or symbol).
– The set of upper and lowercase letters, numbers,
and other symbols is called the ASCII character set.
1-10
• For more info, see
http://computer.howstuffworks.com/bytes1.htm
1-11
Units of Memory
• Kilobyte (K): 1024 bytes
• Megabyte (MB): 1024 kilobytes
• Gigabyte (GB): 1024 megabytes
• Terabyte (TB): 1024 gigabytes
1-12
Types of Files
• Besides the size, there are two types of files:
– ASCII text files contain ASCII characters
– Binary files contain characters that cannot be typed
on the keyboard, generated by software
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Units of Memory (see p. 16)
1-14
The Internet
• The Internet is a network of networks that are
spread all over the world.
• Networks that are geographically close are
called Local Area Networks (LANs).
– Often in the same building
– The university’s network is a prime example
• The Internet is a largely heterarchical network
containing many individual LANs.
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Some Network Basics
• A computer network is two or more computers
connected together so that they can
communicate.
1-16
Some Network Basics (cont.)
– Computers connected to a network are commonly
called hosts.
– The connection that carries data among hosts is
called the transmission medium.
1-17
Network basics (cont.)
• All the hosts on the network must somehow
share the transmission medium.
• Only one data transfer can take place at a time on the
transmission medium. (Draw the diagram.)
– This means that if host A is transferring data to host B, and host
C needs to transfer data to host D, host C must wait until host A
is done before it begins its transfer.
– If host A is transferring a lot of data to host B, host C could end
up waiting a long time.
– For this reason, it’s not desirable to give host A exclusive access
to the transmission medium until it’s done with its transfer.
– Instead networks use a system to ensure that access to the
transmission medium is shared equally among all connected
hosts. This system is called packet switching.
1-18
Packet switching (see p. 73-74, also)
• Packet switching avoids network delays by
ensuring that access to the transmission
medium is shared equally by all hosts.
– Each host that has data to transfer is given a turn.
– During its turn, each host gets exclusive access to
the transmission medium.
1-19
Packet switching (cont.)
– However, the total amount of data it’s allowed to transfer
during its turn is strictly limited.
• The largest amount of data a single host is allowed to transfer during
one turn determines the size of a single packet.
• Data that is bigger than the packet size for the network must be
broken up into multiple packets.
• If a host needs to send multiple packets, it must wait for later turns to
send the others.
• No host is allowed to send more than one packet per turn.
1-20
Packet switching (cont.)
– Every packet is labeled with the identity of the host
that sent it and the identity of the host for which it’s
destined.
• Every host on a given network must therefore have a
unique identity.
– Host identities are called addresses.
– Every network must have rules to determine how these identities
are assigned.
• And every packet must be constructed and labeled
according to a common set of rules as well.
• When we need common rules for computers to follow,
we define protocols.
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Packet Example
As an example, let's look at how an e-mail message might get broken
into packets. Let's say that you send an e-mail to a friend.
The e-mail is about 3,500 bits (3.5 kilobits) in size.
The network you send it over uses fixed-length packets of 1,024 bits (1
kilobit).
The header of each packet is 96 bits long and the trailer is 32 bits long,
leaving 896 bits for the payload (actual message).
To break the 3,500 bits of message into packets, you will need four
packets (divide 3,500 by 896).
Three packets will contain 896 bits of payload and the fourth will have
812 bits. Here is what one of the four packets would contain:
From http://computer.howstuffworks.com/question525.htm
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Packet Example (cont.)
From http://computer.howstuffworks.com/question525.htm
1-23
Heterarchical vs. hierarchical
• A heterarchical network contains many nodes
that are interconnected.
• A hierarchical network contains a tree-like
structure where some nodes are superior to
others.
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Heterarchical vs. hierarchical (cont.)
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Heterarchical vs. hierarchical (cont.)
• A characteristic of a heterarchical network is that it is a
robust network.
• If some nodes are removed, data can still be sent
between nodes
• Hierarchical networks do not lend themselves to
robustness
• The Internet also has dynamic routing, where the
route of the data is determined at the time of
transmission based on current network conditions.
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Host Machines and Host Names
• Each computer on the Internet is a host
machine.
• Each computer has a unique Internet Protocol
(IP) address, such as 124.110.24.1
– Some computers have a permanent IP address
– Some computers borrow an IP address while they
are connected to the Internet
• An IP address is not human-friendly
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IP addresses
• Because there are so many computers on the
Internet, IP addresses must be very large
numbers.
– Since it’s hard to work with very large numbers
accurately, IP addresses are commonly written using
dotted quad notation.
• Dotted quad notation consists of four numbers (in the
range 0 to 255) separated by dots (or periods)
• For example, 137.177.137.7 is the IP address for the
cisunix computer named turing
1-28
Assignment of IP addresses
• Every single computer added to the Internet must be
given an IP address that is not already in use.
• With millions of computers already on the Internet and
thousands more being added every day, that’s a
considerable challenge.
• It’s not practical for each individual computer user to
come up with their own unique IP address.
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Assignment of IP addresses (cont.)
• Since virtually all connections to the Internet are
managed by an organization of some sort (school,
company, ISP, etc.), it’s much more practical to place
each organization in charge of its own addresses.
– When an organization first establishes a connection to the
Internet, it is assigned an address space consisting of the
first one, two or three values in a dotted quad address.
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Assignment of IP addresses (cont.)
– Once assigned such an address space, the
organization is free to assign the remaining three,
two or single values as it sees fit to each computer it
connects to the Internet.
– No other organization is entitled to create addresses within that
assigned address space.
– And the organization that owns a given address space is solely
responsible for ensuring that no address within that space is ever
in use by two computers at the same time.
– At UNH, our address space consists of all addresses that begin
with 132.177.
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Assignment of IP addresses (cont.)
• Remember:
– IP addresses are assigned in a delegated manner.
– Users are assigned IP addresses by organizations
(UNH, Internet service providers (ISPs), etc.
• ISPs obtain allocations of IP addresses from a
local Internet registry (LIR) or national Internet
registry (NIR), or from their appropriate
Regional Internet Registry (RIR):
http://www.iana.org/ipaddress/ip-addresses.htm
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Host Machines and Host Names
• The IP address for most host machines are
mapped to a Domain Name Service (DNS)
address in order to be more people-friendly.
• The DNS address consists of a host name
followed by a domain name
• Example DNS Address: mail.yahoo.com
– Host Name is: mail
– Domain Name is: yahoo.com
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Host Machines and Host Names
• Each domain name consists of:
– Institutional site name
– Top Level Domain name (TLD)
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Host Machines and Host Names
• Examples of TLDs include:
–
–
–
–
–
–
–
.com
.edu
.net
.au
.fr
.hk
.es
a commercial organization
a US educational site
a network site
Australia
France
Hong Kong
Spain
• New TLDs have been added as the original set became
overloaded. Examples?
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• Example: cs.unh.edu
– Host name?
– Domain Name?
– Top Level Domain?
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Domain Names
• Anyone can register a DNS address
• When you type in a DNS address, a domain
name server translates it into an IP address.
1-37
Assignment of hostnames
• Since hostnames, like IP addresses, establish
identities for hosts, they too must be unique
across the entire Internet.
– Recall that with IP addresses, an organization is
assigned a unique address space when it connects to
the Internet.
– At the same time, an organization also typically
obtains a unique domain name.
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Network Information Center (NIC)
• The InterNIC Website!
• This website has been established to provide the
public information regarding Internet domain
name registration services.
• http://www.internic.net/
1-39
Speed and Bottlenecks
• When you go online, your computer exchanges
data with other computers.
• The transfer of data is measured in bits per
second (bps); bandwidth
• Your data transfer rate is determined by:
– The type of connection (e.g. dial-up) (see p. 68)
– The traffic over the network
• The bottleneck is the part of your connection
that slows the data rate during transfer
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The Client/Server Software Model
• Clients and servers are host machines.
• A client is the host machine that requests
information from the server.
• The server is a resource that provides a service
for (many) clients.
• The client/server interaction is the
foundation for all Internet communication.
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The Client/Server Software Model
1-42
Internet services
What the Internet allows us to do is determined
by the services that it provides.
– When we are using the Internet, we are utilizing one
or more of these Internet services.
• World Wide Web allows self-publication in electronic formats.
• E-mail allows directed communication with other Internet users.
• Remote login allows computers to be controlled remotely by users
on other computers.
• File transfer allows files to be moved and copied between various
computers.
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The World Wide Web and Web Browsers
• The Web and the Internet are not the same.
• The World Wide Web has become a popular
means of accessing information and services.
• A Web browser is the software necessary to
view information.
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The World Wide Web and Web Browsers
• Navigating the Web only takes a few commands.
• The information in the Web is organized as
hypertext, graphics, video, and sound.
• The text in a Web page may contain hyperlinks
that, if clicked, allows you to view related
information on other Web pages.
• You control where you go and what information
you see via these hyperlinks.
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The World Wide Web and Web Browsers
• A Web page is a document on the Web that you
view through your Web browser.
• The act of reading Web pages and clicking on
hyperlinks is called browsing (basically,
exploring).
• Each Web page has a unique address called a
Uniform Resource Locator (URL) that you
can use to jump directly to it.
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URL Uniform Resource Locator
• URL
Represents the
address of a
resource on the
Internet.
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How to Get Online
• Before you can use Internet resources, you need
to get access to the Internet.
• Many students use their accounts on university
computers.
• Others use the computers at the library, their
workplace, or even that of a friend.
• Others will need to get an account and software
through a commercial Internet Service
Provider (ISP). Examples?
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How to Get Online (cont.)
• An ISP provides technical support for the
provided software.
• Your account gives you a userid and password.
1-49
Browser Tips and Tricks
• Select your own default home page
– When you start your browser, a default Web page is
displayed.
– You can change the default page to another URL.
• Use the Find command
– Find allows you to find text in a page.
– You enter the text that you want to find.
– If that text is in the page, then you view the first
instance of the text in the page.
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Browser Tips and Tricks (cont.)
• Use your History list
– The History list is a list of the URLs that you have visited
recently.
– You can click on a URL from the list to revisit the page.
• Abort a download if you get stuck
– If the browser appears to be stuck while loading a page,
select the option to stop the page loading.
– The page may display, but if not try clicking on the link
again.
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Browser Tips and Tricks (cont.)
• Use Bookmarks (Favorites)
– A bookmark is a pointer to a Web page that you
expect to revisit.
– You can select a bookmark from a list, and quickly
jump to that Web page.
• Add Bookmarks with care
– Bookmarking every page of interest is tempting.
– Large bookmark lists are difficult to use.
– Create folders for your bookmarks.
1-52
Browser Tips and Tricks (cont.)
• Turn off graphics
– Graphics files can be large and take a long time to
download.
– If you are in a hurry or have a slow Internet
connection, then you may spend time waiting for
pages to load.
– You can set your browser to not download graphics.
1-53
Browser Tips and Tricks (cont.)
• Use the Phishing Filter
– Phishing is a form of Social Engineering (see
Chapter 2) designed to get unwary users to enter
sensitive information (like passwords or account
numbers) for nefarious purposes.
– Your browser warns you when visiting a known
phishing site.
– But - your browsing history must be monitored to
enable this feature.
1-54
Dear Amazon Member,
We recently noticed an attempt to log in to your Amazon account from a foreign Ip
address and we have reason to believe that your account was used by third party
without your authorization.
If you recently accessed your account while traveling,the unusual log in attempts
may have been initiated by you.Therefore,if you are the rightful account holder,
click on the link below to log into your account and follow the instructions.
http://www.atlas-hs.com/rafa/amazon/SignIn.htm
if you choose to ignore our request,you leave us on choice but to temporarily
suspend your account.
If you received this notice and you are not authorizes account holder,please be
aware that it is in violation of Amazon policy to represent oneself as another Amazon
user.Such action may also be in violation of local,rational,and/or international law.
Amazon is committed to assist law enforcement with any inquires related to attempts
to misappropriate personal information with the intent to commit fraud or theft.
Information will be provided at the request of law enforcement agencies to ensure that
impersonators are prosecuted to the fullest extent of the law
Thank you for your patience as we work together to protect your account
Sincerely,
Amazon Account Review Department
1-55
Browser Tips and Tricks (cont.)
• Don’t let a “404 Not Found” message stop you.
– The error means that the specified URL was not
found.
– Check that the URL was correct.
– The page may have been removed or moved .
– You can always backtrack through the URL to
see if a related part of the site is available.
– HOW?
http://wps.aw.com/aw_lehnert_web101_3/chapter1/file.html
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Browser Tips and Tricks (cont.)
• Avoid peak hours
– The Internet has times of high traffic where
response times are slower than off-peak times
– In the US, the peak times of usage during the week
are:
• The middle of the day
• Early evenings
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Browser Tips and Tricks (cont.)
• Other Useful browser Features found on page 49
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–
–
–
–
–
–
–
Automatic Update
Bookmark Import/Export
Bookmark manager
Content Advisor
Cookie Manager
Customization
Download Manager
Form Manager
1-58
Browser Tips and Tricks (cont.)
• Other Useful browser Features (cont.)
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–
–
–
–
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History Manager
Integrated Search
Javascript Disable
Password Manager
Pop-up Blocker
RSS Feeds
Security Manager
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Alternate Web Browsers (pp. 51 – 58)
• Firefox
– Available for Windows and Mac
– Replaces the aging Mozilla browser
– http://www.mozilla.com/firefox/
• Mozilla (aka SeaMonkey)
– Available for Windows and Mac
– Includes web page editor, mail client, Usenet News reader,
IRC Chat cient
– http://www.mozilla.org/projects/seamonkey
– http://www.mozilla.org/products/mozilla1.x/
1-60
Alternate Web Browsers
• Netscape
–
–
–
–
Available for Windows and Mac
Based on Firefox browser
Includes integrated Security Center
http://www.netscape.com/
• Opera
– Available for Windows and Mac
– Includes widgets and a BitTorrent client (see Section 6.4.1)
– http://www.opera.com/
1-61
Mac Only Web Browsers
• Safari
– Includes “Private Browsing” feature which keeps no record
of sites visited
– http://www.apple.com/
• Camino, iCab, Shiira
– http://www.mozilla.org/ (Camino)
– http://www.iCab.de/ (iCab)
– http://hmdt-web.net/ (Shiira)
1-62