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Technology in Action
Chapter 13
Behind the Scenes: How the Internet Works
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
The Management of the Internet
• Ownership of the Internet
– Local networks are owned by
• Individuals
• Universities
• Government agencies
• Private companies
– Infrastructure (high-speed data lines) is
owned by
• Government entities
• Privately held companies
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The Management of the Internet (cont.)
•
Management the Internet
–
Nonprofit organizations and user groups
•
Each have a specialized purpose
•
Previously handled by U.S. government contractors
–
•
•
Changed because of global nature of the Internet
Guarantees worldwide engagement in the direction of the Internet
Paying for the Internet
–
–
National Science Foundation (NSF)
•
Pays for large part of infrastructure
•
Funds research and development for new technologies
•
Through federal taxes
Other countries participate as well
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The Management of the Internet (cont.)
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Internet Networking
Internet Data Routes
•
How computers are connected
to the Internet
– Internet is a “network of
networks”
• Similar to U.S.
highway system
– Main paths known
collectively as the Internet
backbone
• Large national and
international networks
• Owned by
commercial,
education, or
governmental
organizations
– Have fastest connections
– Bandwidth needs determine
what kind of line is used
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Internet Networking
Internet Data Routes (cont.)
•
How individuals connect to an ISP
–
–
Point of presence (POP)
•
A bank of modems, servers, routers, and switches
•
Many users can connect simultaneously
ISPs maintain multiple POPs throughout the geographic area they serve
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Internet Networking
The Network Model of the Internet
• The network model the Internet uses
– Client/server model
– Clients are
• Devices such as computers, tablets, and
smartphones
• Clients use browsers to request services
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Internet Networking
The Network Model of the Internet (cont.)
• The network model the Internet use (cont.)
– Types of servers
• Web servers: Run specialized operating systems
to host web pages and other information
• Commerce servers: Software that enables users
to buy goods and services; use security protocols
to protect sensitive information
• File servers: Provide remote storage; cloud
storage
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Data Transmission
and Protocols
• Network follows standard protocols to send information
• Protocol is a set of rules for exchanging electronic information
• Could be considered the rules of the road for the information
superhighway
– Open systems – the design of protocol is made public for access
by anyone
– Proprietary system – private system which was the norm
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Data Transmission
and Protocols (cont.)
• Problems in developing an open system
Internet protocol
– Agreeing on standards was easy
– Developing a new method of communication
was tough
• Circuit switching (technology available in the
1960s) was inefficient for computer
communication
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Data Transmission and Protocols
Circuit Switching
• Why we don’t use circuit switching to
connect two computers
– Used since early days of telephone
– Dedicated connection is formed between two
points
– Connection remains active for duration of
transmission
– Important when order of receiving information
is critical
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Data Transmission and Protocols
Circuit Switching (cont.)
• Why we don’t use circuit switching to
connect two computers (cont.)
– Inefficient when applied to computers
– Computers transmits data in a group, or burst
– Processor works on next task and ceases to
communicate until ready to transmit next burst
– Would need to keep circuit open, therefore
unavailable or have to be reestablished for
each burst
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Data Transmission and Protocols
Packet Switching
• What computers use to communicate
– Packet switching makes computer
communication efficient
– Doesn’t require a dedicated communications
circuit
– Data is broken into smaller chunks (packets
or data packets)
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Data Transmission and Protocols
Packet Switching (cont.)
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Data Transmission and Protocols
Packet Switching (cont.)
• What computers use to communicate
(cont.)
– Packets are sent over various routes at same
time
– They are reassembled at the destination by
receiving computer
– Fulfilled original goal of Internet: Data can still
travel to destination if a node is disabled or
destroyed
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Data Transmission and Protocols
Packet Switching (cont.)
• What information a packet contains
1. An address to which the packet is being sent
2. The address from where the packet
originates
3. Reassembly instructions, if the original data
is split between packets, and
4. The data that’s being transmitted
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•
Animation of packet switching….
– http://en.wikipedia.org/wiki/Packet_switching
•
TCP/IP data packet structure
– http://www.thegeekstuff.com/2012/03/ip-protocol-header/
•
https://www.youtube.com/watch?v=3mQK8uyKrFU
•
Network Switches & routers
–
https://www.youtube.com/watch?v=Ofjsh_E4HFY
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•
Review of terms
–
Proxy server - a server (a computer system or an application) that acts as an intermediary for
requests from clients seeking resources from other servers. A client connects to the proxy
server, requesting some service, such as a file, connection, web page, or other resource
available from a different server and the proxy server evaluates the request as a way to
simplify and control its complexity. Proxies were invented to add structure and encapsulation
to distributed systems.[
–
Network Switch - a computer networking device that connects devices together on a
computer network, by using a form of packet switching to forward data to the destination
device.
–
Router - a networking device, commonly specialized hardware, that forwards data packets
between computer networks. This creates an overlay internetwork, as a router is connected
to two or more data lines from different networks. When a data packet comes in one of the
lines, the router reads the address information in the packet to determine its ultimate
destination. Then, using information in its routing table or routing policy, it directs the packet
to the next network on its journey. Routers perform the "traffic directing" functions on the
Internet. A data packet is typically forwarded from one router to another through the networks
that constitute the internetwork until it reaches its destination node.[1
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Data Transmission and Protocols
Packet Switching (cont.)
• Why packets take different routes, and
how do they decide which route to use
– Routers monitor traffic and decide most
effective route
– Windows utility tracert shows details of exact
route request takes to destination server
• Tracert google.com and www.cityoflondon.gov.uk
• Ping google.com
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Data Transmission and Protocols
TCP/IP
• What protocol the Internet uses for
transmitting data
– Main suite of protocols is TCP/IP
• Transmission Control Protocol (TCP)
• Internet Protocol (IP)
– Consists of many interrelated protocols
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Data Transmission and Protocols
TCP/IP (cont.)
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Internet Identity: IP Addresses
and Domain Names
• Each computer, server, or device
connected to the Internet is required to
have a unique number
• IP address is the unique number
• Humans remember words better than
numbers
• Domain names are word-based IP
addresses
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Internet Identity: IP Addresses and Domain Names
IP Addresses
• IP address
– A unique identification number that defines
each device connected to the Internet
– Fulfills same function as a street address
– Must be registered with the Internet
Corporation for Assigned Names and
Numbers (ICANN)
• Ensures their uniqueness
• Allocates to network administrators
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• What an IP address looks like
– Typical IP address: 197.169.73.63
– Referred to as a dotted decimal number
(dotted quad)
– Binary form is
11000101.10101001.01001001.00111111
– Each is referred to as an octet
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• What an IP address looks like
– IP addresses are considered 32-bit numbers
– Can represent 4,294,967,296 values
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• Limited number of IP addresses
– Internet Protocol version 4 (IPv4) was created
in 1981 before explosive growth of Internet
– IPv4 offers a fixed number of IP addresses
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
•
Other Internet addressing systems
– Internet Protocol version 6 (IPv6), developed by IETF, uses 128-bit addressing
instead of 32-bit
•
Internet Engineering Task Force (IETF)
•
https://www.ietf.org/
•
Internet Engineering Task Force
– XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX
•
Each X is a hexadecimal digit
•
Hexadecimal is base-16 number system
•
Uses 0-9 or A-F
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• Other Internet addressing systems (cont.)
– IPv6 provides virtually unlimited supply of IP
addresses
– All modern operating systems handle both
IPv4 and IPv6
– Majority of routing still uses IPv4
– IPv6 conversion will happen soon as IPv4
addresses are running out
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• How my computer gets an IP address
(either/or)
– Static
• IP address never changes
• Assigned by network administrator or ISP
– Dynamic
• IP address is temporary
• Assigned from a pool of addresses
• More common
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• How dynamic addresses are assigned
– Handled by Dynamic Host Configuration
Protocol (DHCP)
– Belongs to TCP/IP protocol suite
– Takes from pool of available addresses on asneeded basis
– Assigns address for duration of session
– Might not be the same from session to
session
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Internet Identity: IP Addresses and Domain Names
IP Addresses (cont.)
• Benefits of dynamic
addressing
– Provides a more secure
environment
– Helps to keep hackers
out of system
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Internet Identity: IP Addresses and Domain Names
Domain Names
• Why IP addresses are not seen
– Domain names take the place of IP address
– Makes it easier for people to remember
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Internet Identity: IP Addresses and Domain Names
Domain Names (cont.)
How my computer knows the IP address of another computer
Computer converts URL to an IP address by consulting a database on
a domain name system (DNS) server
Functions like a phone book for the Internet
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Internet Identity: IP Addresses and Domain Names
Domain Names (cont.)
•
Controlling domain name registration
– ICANN assigns companies or organizations to manage registration
– One company is assigned each TLD
– Maintains a database of all registered domains and contact information
– . VeriSign is the current ICANN-accredited domain name registrar for
the .com and .net domains. VeriSign provides a database that lists all
the registered .com and .net domains and their contact information. You
can look up any .com or .net domain at Network Solutions
(networksolutions.com) to see whether it’s registered and, if so, who
owns it.
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Internet Identity: IP Addresses and Domain Names
Domain Names (cont.)
•
How domains are organized
– Organized by level
– Portion after the dot is the top-level domain (TLD)
– Establish by ICANN
• ICANN
• https://www.icann.org/
• The Internet Corporation for Assigned Names and Numbers (ICANN)
– Within TLDs are many second-level domains
•
Needs to be unique within its TLD
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Internet Identity: IP Addresses and Domain Names
Domain Names (cont.)
• Controlling domain name registration
(cont.)
– Country-specific domains are controlled by
groups in those countries
– Complete list of TLDs are found on Internet
Assigned Numbers Authority site (iana.org)
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HTML, XML, and other web Building Blocks
HTML
• How web pages are formatted
– Hypertext Markup Language (HTML)
•
Not a programming language
•
Set of rules for marking blocks of text
•
Browser knows how to display them
•
Surrounded by pairs of HTML tags
•
Tags and text are referred to as an element
•
<b><i>This should be bolded and
italicized.</i></b>
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HTML, XML, and other web Building Blocks
HTML (cont.)
• Viewing the HTML coding of a web page
– HTML documents are text documents with
tags applied
– Right-click, then select View Source
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HTML, XML, and other web Building Blocks
HTML (cont.)
• Current HTML standard
– HTML5 is current version; should be finalized
by 2014
– Modernizes features, such as
•
Reducing need for external plug-ins (like Flash)
•
Supporting better error handling
•
Introducing new tags to support media, like
<video> and <audio>
•
Making it easier to draw graphics
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HTML, XML, and other web Building Blocks
HTML (cont.)
• How developers can easily change the
formatting of HTML elements
– Cascading style sheet
•
List of rules that define in one location how to
display HTML elements
•
Enable a web browser to define formatting for
each element
•
Acts as a template
•
Allows global changes to be done easily
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HTML, XML, and other web Building Blocks
HTML (cont.)
• Where the cascading comes in
– Different layers of styles
•
External: Stored in a separate file
•
Embedded: Stored in the current document
•
Inline: Stored in a single line in the document
– Different rules can be created for the same
type of element in different places
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HTML, XML, and other web Building Blocks
HTML (cont.)
• Where the cascading comes in
– Style sheets are merged
– If conflict in rules, then rules are weighted in
hierarchy (cascade)
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HTML, XML, and other web Building Blocks
HTML (cont.)
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HTML, XML, and other web Building Blocks
XML
• How XML is different from HTML
– eXtensible Markup Language (XML)
describes what data is described rather than
how it is to be displayed
– Users build own markup languages to
accommodate data formats and needs
– Provides method of data validation through
XML schema diagrams (XSD)
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HTML, XML, and other web Building Blocks
XML (cont.)
• Custom XML packages
– XML has spawned custom packages for
specific communities
– Goal is information exchange standards that
can be easily constructed and customized to
serve growing variety of online applications
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HTML, XML, and other web Building Blocks
Web Browser Protocols
• Internet protocol a browser uses to send
requests
– Hypertext Transfer Protocol (HTTP) was
created for the transfer of hypertext
documents
– Hypertext documents have text that is linked
to other documents or media
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HTML, XML, and other web Building Blocks
Web Browser Protocols (cont.)
• How a browser safeguards secure
information
– Hypertext Transfer Protocol Secure (HTTPS)
ensures data security
– Combination of HTTP and Secure Sockets
Layer (SSL), a network security protocol
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HTML, XML, and other web Building Blocks
Web Browser Protocols (cont.)
• How a browser safeguards secure
information (cont.)
– Transport Layer Security (TLS) is an updated
extension of SSL
– These provide data integrity and security for
transmissions over the Internet
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HTML, XML, and other web Building Blocks
Server-Side Applications
• Server-side applications
– Web is a client/server network
– Program on server is considered server-side
– Can require many communication sessions
between client and server
– Can perform very complex operations
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• Popular server-side programming choices
– CGI (Common Gateway Interface)
– ASP.NET (Active Server Pages)
– VBScript
– PerlScript
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• How CGI makes a web page more
interactive
– Most browser requests result in file being
displayed in browser
– Some programs can perform actions, such as
gathering a name and address and adding it
to a database
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• How CGI makes a web page more
interactive (cont.)
– Common Gateway Interface (CGI) provides
methodology that allows a browser to request
that a program file be executed
– Allows functionality beyond simple display of
information
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• Programming language used to create a
CGI program
– Can be created in almost any language
– Known as CGI scripts
– Common languages include
•
Perl
•
C
•
C++
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• Programming language used to create a
CGI program (cont.)
– Almost any task can be accomplished
through a CGI script
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• How CGI programs are executed
– CGI bin (directory) is created and all CGI
scripts go into this directory
– These files aren’t just read and sent, they
need to be run
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HTML, XML, and other web Building Blocks
Server-Side Applications (cont.)
• How CGI programs are executed (cont.)
– Example
Step 1: A button gives a message
Step 2: Clicking the button executes a script
Step 3: Script generates a form
Step 4: Form information is sent back to server and recorded in
database
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HTML, XML, and other web Building Blocks
Client-Side Applications
• Client-side applications
– Program that runs on client computer
– Requires no interaction with web server
– New data is only sent in response to a
request
– Exchange of data can make interactivity
inefficient and slow
– More efficient to run client-side programs on
local computer
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• How client-side programming is done
– HTML embedded scripting language tucks
programming code directly in HTML tag
•
Most popular is JavaScript
– Applet (small application) is downloaded to
client and runs when needed
•
Most common language is Java
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• Delay in downloading an applet
– There is some delay but once downloaded it
executes without further communication with
server
– Example
Step 1: Browser makes request
Step 2: Server returns Java applet
Step 3: Computer executes the code
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• Scripting technologies
– Dynamic HTML (DHTML) combines HTML,
cascading style sheets, and JavaScript
– Creates lively and interactive websites
– Allows a web page to change after it’s been
loaded
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• Scripting technologies
– Occurs in response to user actions
– Brings special effects without downloading
and installing plug-ins or special software
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• JavaScript
– Commonly used scripting language
– Creates DHTML effects
– Not the same as Java programming
language
– Allows HTML documents to respond to
mouse clicks and typing
– All actions are executed on the client
computer
– Keeps web pages from being lifeless
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• How JavaScript controls the components
of a web page
– Document Object Model (DOM) is used to
organize objects and page elements
– Defines every item on a web page as an
object
– Allows web developers to easily change the
look and feel of objects
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
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HTML, XML, and other web Building Blocks
Client-Side Applications (cont.)
• Where web programming is headed
– Web pages interacting with servers at times
other than when being fetched
– Ongoing exchange of information
– Updating information without page refresh or
leaving the page
– AJAX (Asynchronous JavaScript and XML)
facilitates these applications
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Communications Over the Internet
E-Mail
• Invention of e-mail
– Ray Tomlinson (1971) helped develop
ARPANET (precursor to the Internet)
– Written to enable users to leave text
messages for each other on a single
machine
– Extended to sending text messages between
machines on Internet
– Became the most popular application
– 1973: Accounted for 75% of all data traffic
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Communications Over the Internet
E-Mail (cont.)
• How e-mail travels the Internet
– Simple Mail Transfer Protocol (SMTP) sends
e-mails along the Internet
– Part of the Internet Protocol suite
– Client/server application
– Passes through several e-mail servers
•
Specialized computers whose sole function is to
store, process, and send e-mail
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Communications Over the Internet
E-Mail (cont.)
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Communications Over the Internet
E-Mail (cont.)
• Where e-mail servers are located
– ISPs have e-mail servers that use SMTP
Step 1: Your ISP’s e-mail server receives your e-mail
Step 2: E-mail server reads domain name and
determines location using a DNS server
Step 3: DNS server turns domain name into IP
address
Step 4: E-mail is forwarded to receiver’s ISP server
Step 5: E-mail is stored on receiver’s e-mail server
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Communications Over the Internet
E-Mail (cont.)
• How we are able to send files as
attachments
– SMTP handles text messages
– Multipurpose Internet Mail Extensions
(MIME) specification created to send files
– E-mail is sent as text, but MIME handles the
encoding and decoding of files
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Communications Over the Internet
E-Mail Security: Encryption
• How other people can read my e-mail
– Highly susceptible to being read because
sent in plain text
– Copies might exist on numerous servers
– Encryption helps protect sensitive messages
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• How to encrypt e-mail
– Many e-mail servers offer built-in encryption
•
Hushmail
•
Comodo SecureEmail
– Can sign up to experiment
– Use secure account when secure
communications are required
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• How encryption works
– Codes e-mail so that only person with key to
code can decode the message
– Private key
– Public key
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Private key encryption
– Only the two parties have the code
– Could be a shift code
– Could be more complex substitution code
– Main problem is key security, code is broken
if:
•
Code is stolen
•
Someone is savvy about decoding
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Public key encryption
– Two keys (key pair) are created
•
One for coding, one for decoding
– Coding key is distributed as public key
•
Message being sent to you is coded using public
key
– Decode using private key
•
Only receiver knows private key
– Mathematical relationship between the two
keys
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Encryption used on the Internet
– Public key is the most common
– Pretty Good Privacy (PGP) is available for
download
– Can generate key pairs to provide private
key if desired
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• What a key looks like
– Binary numbers
– Vary in length depending on security needs
– Key and message run through complex
algorithm converts text into unrecognizable
code
– Each key generates different code
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Private key’s level of security
– Impossible to deduce private key from public
key because of complexity of algorithms
used
– In brute force attack every possible
combination is tried
– Can enable hackers to deduce key and
decode message
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Safe key
– 1990s: 40-bit keys thought to be completely
resistant to brute force attacks
– 1995: French programmer broke 40-bit key
– 128-bit keys became standard
– Strong encryption calls for 256-bit keys
•
Could take hundreds of billions of years to crack
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Communications Over the Internet
E-Mail Security: Encryption (cont.)
• Encryption used in corporations
– Paid services include
•
Confirmation of message delivery
•
Message tracking
•
Overwriting of e-mail messages when deleted
– Securus Systems and ZixCorp provide these
services
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Communications Over the Internet
Instant Messaging
• What you need to run instant messaging
– Client program that connects to an instant
messaging (IM) service
– Examples
•
Yahoo! Messenger
•
GoogleTalk
•
Windows Live Messenger
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Communications Over the Internet
Instant Messaging (cont.)
• How instant messaging works
– Client software makes a connection with
chat server
– Provides connection information to your
device
– Because friend’s device and your device
have same connection information, server
isn’t involved in chat session
– Chatting takes place directly between two
devices over the Internet
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Communications Over the Internet
Instant Messaging (cont.)
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Communications Over the Internet
Instant Messaging (cont.)
• IM security
– Most do not use high level of security
– Vulnerable to
•
Viruses
•
Worms
•
Hacking threats
•
Eavesdropping
– Increased security is in development
– Employers can monitor IM sessions
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Chapter 13 Summary Questions
1. Who owns, manages, and pays for the
Internet?
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Chapter 13 Summary Questions
2. How do the Internet’s networking
components interact?
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Chapter 13 Summary Questions
3. What data transmissions and protocols
does the Internet use?
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Chapter 13 Summary Questions
4. Why are IP addresses and domain names
important for Internet communications?
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Chapter 13 Summary Questions
5. What web technologies are used to
develop web applications?
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Chapter 13 Summary Questions
6. How do e-mail and instant messaging
work, and how is information using these
technologies kept secure?
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Publishing as Prentice Hall