technology in action chapter 13 behind the scenes: how the internet works copyright © 2013 pearson...

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

Copyright © 2014 Pearson Education, Inc. Publishing as Prentice Hall 2

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


The Management of the Internet (cont.)


Internet NetworkingInternet 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


5

Internet NetworkingInternet 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


Internet NetworkingThe 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


Internet NetworkingThe 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


Data Transmissionand 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


Data Transmissionand 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


Data Transmission and ProtocolsCircuit 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


Data Transmission and ProtocolsCircuit 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


Data Transmission and ProtocolsPacket 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)


Data Transmission and ProtocolsPacket 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



• 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


• 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


http://en.wikipedia.org/wiki/Packet_switching



http://www.thegeekstuff.com/2012/03/ip-protocol-header/



https://www.youtube.com/watch?v=3mQK8uyKrFU

https://www.youtube.com/watch?v=3mQK8uyKrFU

• 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


http://en.wikipedia.org/wiki/Server_(computing)

http://en.wikipedia.org/wiki/Client_(computing)

http://en.wikipedia.org/wiki/Proxy_server#cite_note-1

http://en.wikipedia.org/wiki/Computer_networking_device

http://en.wikipedia.org/wiki/Computer_network


http://en.wikipedia.org/wiki/Data_packet

http://en.wikipedia.org/wiki/Computer_network

http://en.wikipedia.org/wiki/Internetwork

http://en.wikipedia.org/wiki/Routing_table

http://en.wikipedia.org/wiki/Routing_policy

http://en.wikipedia.org/wiki/Internet

http://en.wikipedia.org/wiki/Router_(computing)#cite_note-1


• 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


Data Transmission and ProtocolsTCP/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


Data Transmission and ProtocolsTCP/IP (cont.)


Internet Identity: IP Addressesand 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

Copyright © 2014Pearson Education, Inc. Publishing as Prentice Hall 22

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



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




• What an IP address looks like– IP addresses are considered 32-bit numbers

– Can represent 4,294,967,296 values




• 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



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


https://www.ietf.org/



• 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




• 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




• 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 as-needed basis

– Assigns address for duration of session

– Might not be the same from session to session




• Benefits of dynamic addressing– Provides a more secure

environment

– Helps to keep hackers out of system



Domain Names

• Why IP addresses are not seen– Domain names take the place of IP address

– Makes it easier for people to remember



Domain Names (cont.)


How my computer knows the IP address of another computerComputer converts URL to an IP address by consulting a database on

a domain name system (DNS) serverFunctions like a phone book for the Internet



• 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.



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




• 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)


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>


• Viewing the HTML coding of a web page– HTML documents are text documents with

tags applied

– Right-click, then select View Source



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



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



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



HTML (cont.)

• Where the cascading comes in– Style sheets are merged

– If conflict in rules, then rules are weighted in hierarchy (cascade)



HTML (cont.)



HTML (cont.)

• 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)



XML

• 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



XML (cont.)

• 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



Web Browser Protocols

• 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



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



Web Browser Protocols (cont.)


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


• Popular server-side programming choices– CGI (Common Gateway Interface)

– ASP.NET (Active Server Pages)

– VBScript

– PerlScript



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




• 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




• 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++




• Programming language used to create a CGI program (cont.)– Almost any task can be accomplished

through a CGI script




• 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




• How CGI programs are executed (cont.)

– ExampleStep 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





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


• 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



Client-Side Applications (cont.)

• Delay in downloading an applet– There is some delay but once downloaded it

executes without further communication with server

– ExampleStep 1: Browser makes request

Step 2: Server returns Java applet

Step 3: Computer executes the code




• 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




• Scripting technologies– Occurs in response to user actions

– Brings special effects without downloading and installing plug-ins or special software




• 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




• 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




• 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




Communications Over the InternetE-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


• 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


Communications Over the InternetE-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



• 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



Communications Over the InternetE-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


• 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


Communications Over the InternetE-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



• 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



• 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



• 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



• 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



• 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



• 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



• 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



Communications Over the InternetInstant 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


• 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


Communications Over the InternetInstant 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



1. Who owns, manages, and pays for the Internet?


Chapter 13 Summary Questions

2. How do the Internet’s networking components interact?



3. What data transmissions and protocols does the Internet use?



4. Why are IP addresses and domain names important for Internet communications?



5. What web technologies are used to develop web applications?



6. How do e-mail and instant messaging work, and how is information using these technologies kept secure?



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