The Internet
Information Systems,
Higher
What is the Internet?
• Started in 1960s for military use
• ARPANET – forerunner of Internet
• 1989 WWW was invented
1990s hardware and telecommunications became cheaper
Internet use became widespread.
1998 – Internet Explorer supplied with Windows 98
Intranet
• Same as internet but restricted to a LAN
• Same software and protocols as Internet
• Gives organisations more control
• Firewall needed between Intranet and Internet.


How does the Internet Work?
Transmission Protocols
• TCP – Transmission Control Protocol
Breaks data into packets at sending end and puts packets back together at receiving end.

• IP – Internet Protocol
Provides routing device with source and destination address
Packet Switching
Packet switching
Internet Hosting
• Host – any hardware component connected to the internet
• Every host has a unique IP address
• Eg 10.120.10.60
Packet Switching
• Routing – the method used to send data packets across the internet
Advantages of TCP/IP and Packet Switching
• Any network or hardware device can communicate with any other
• Can take any route from source to destination
• If any server or router is down the packet takes a different route
• Communications channels are used more efficiently as packets from many users can use same channel.
Server Side Hardware
• Server – Powerful computer
– Used to store data for other computers to access
– (eg web server, mail server)
• Routers and Routing tables
– Router stores and forwards data packets
– Checks IP address on packet, then checks routing table for best route.
– Routing table is database containing info about all network paths
– Routing tables are constantly updated

Internet Service Protocols
• HTTP – HyperText Transfer Protocol
Transfers and downloads web pages

• FTP – File Transfer Protocol
uploading and downloading of large files

• SMTP – Simple Mail Transfer Protocol
for sending Email between servers

• POP – Post Office Protocol
Used to retrieve Email from a mail server



Revision of Protocols
• New hardware and software – compatibility issues
• New protocols eg VOIP
Standard URL Structure
Proxy Server
• Sits between the client application and real server
• Intercepts requests to real server to see if it can fulfil the request itself.


Domain Name Server (DNS)
• Resolves a URL into the correct IP address
• User enters URL
• Browser accesses database of IP addresses through ISP
• Network of databases is accessed till IP address is matched to URL
• Process is called
HOST NAME RESOLUTION
IP Addresses always have 32 bits
IP Addresses
• Split into network ID and host ID
• 5 main types of IP address classes depending on network type and size
• 3 most commonly used are
• Class A, Class B, Class C
Class A IP Address
Class B IP Address
Class C IP Address

Examples
• 12.140.60.14
• 140.45.45.96
• 201.35.120.34
Network mask
• Used to separate network ID from host ID

Sub-net mask
• Allows a network to be divided into “sub networks”
• Network administrator can divide the host part into 2 or more subnets.
Example using a class B IP address
Example using a class B IP address
Subnet mask part of the Octet

• 192 11000000 2 sub networks
• 124 11100000 6
• 140 11110000 14
Example
For a class C network how many sub networks will the subnet mask 255.255.255.192 have?

Gateway Address
• Gateway is a link between 2 different networks.
• Each gateway address belongs to a different subnet.
• Router applies subnet mask and sends packets to correct network.
TELNET
• Allows a user to remotely control a server
• Log on with valid user ID and password
• Enter commands and they will be executed as if you were entering them directly at the server console
Revision of Protocols
• Revised and new protocols are developed due to
• Incorporation of new technology eg video streaming, mobile internet.
• New services eg VOIP
Internet Regulatory Bodies
• IANA
• Internet Assigned Numbers Authority
• Administers IP addresses and top level domains
• 2 types of top level domains
• Country codes and generic codes
Internet Regulatory Bodies
• Register domain names
• Transfer and cancel domain names
• Domain names have to be assigned an IP address for DNS
Internet Regulatory Bodies
• W3C
• World Wide Web consortium
• Technical developments on WWW such as..
• Changes to HTML, XML, PNG
Social, Ethical and Legal Implications
Social
Ethical Implications
• Censorship?
• Privacy?
Data Protection Act (1998)
Data subject can
Data Protection Act (1998)
• 1984 act only covered data in electronic format.
• 1984 Act applied only in UK
• 1998 Act harmonised EU Data protection legislation.
Exemptions from DPA
Problems with DPA
• Personal Data held on web servers
• Guest books
Computer Misuse Act
• Hacking
• Sending viruses
• Service denial
– Server bombarded with millions of requests
• Copying of files
International Agreements
Viruses and Spyware/Adware
• Anti virus software
• Anti Spyware software
• Must be updated regularly
• Firewall is essential, especially with broadband connection.
Protection of Systems and Networks
• Packet filtering routers
-Filter out packets that come from certain IP addresses
Only checks IP address, does not read content
• Firewall
Only allows packets from named IP addresses through
Can read contents of packet as well as IP address.


Protection of Systems and Networks
• Proxy Server

Proxy Server
• Sits between the client application and real server
• Intercepts requests to real server to see if it can fulfil the request itself.

Protection of Systems and Networks
• Encryption
• Data is coded at sending end and decoded at receiving end.
• Encryption key (A mathematical formula) is used to code and decode the data.

Protection of Systems and Networks
• Uses public and private keys
• Public key used to code (encrypt) data
• Private key used to decode data
Protection of Systems and Networks
• RSA requires complicated calculations on every character sent
• Slow
• PGP is faster
• One computer creates a symmetric key and sends it to receiving computer using public key encryption (RSA)
• Computers communicate using symmetric key encryption
• New symmetric key created each session

Secure Socket Layer (SSL)
• Protocol used to provide an encrypted link.
• Secure servers are given a certificate by certificate authority
• Server sends digital certificate to browser
• Link is encrypted as well as the data
• Used by browsers.
• Combination of send and receive ports is called a socket
Digital signature
• Piece of encrypted data added to a document
• To give authenticity
Site tracking
• Depends on sending and receiving of cookies
• Text file placed on your hard disk by a web server
• When you request a web page browser checks for cookie
• Sends ID from cookie with URL
• If no cookie browser creates one.
• Eg hit counter on a web page
• Web servers have log files
• Big privacy issues
Internet Resources(web pages)
•Academic
•Commercial
•Personal
Academic Resources
• Edutainment
• e-books
• e-learning
Eg BBC Bitesize
• Web-based training
• Virtual libraries
• e-journals
• University, college and school websites
Commercial Resources
• e-commerce
• e-banking
• Airline reservations
• e-marketplace
• advertising
Personal Resources
• Computer games
• Multi-user games
• News and weather
• Music and video download sites
• Personal websites
Assessment of Web Resource Information
• Accuracy
• Bias
• Credibility
Browser
Application program that allows you to download and interact with web pages.
Eg MS Internet Explorer

Browser Facilities
• HTML interpretation
(interprets HTML instructions to display the web page
• capture graphics and text from web pages
• Set home page
• Security/privacy options
• File transfer
• Client side scripting
• Cookie functions
• Built in encryption functions
Authoring tools
• Icon based – click icons to add features to web page (no knowledge of HTML needed)
• Web tools
– eg hyperlink tool,
• Scripting tools
– Allow extra HTML code to be added to add extra features to page
• Save as web page
Hyperlink
• Text or graphic which when clicked takes you to another file or web page
Creating a Website
• 3 types of authoring software

Why use web authoring packages?
• User friandly
• Templates
• Wizards
• No knowledge of HTML required
• Facilities for uploading of web pages
Why Use HTML?
• Increases download efficiency as less unnecessary html script is generated
• Make specific changes to HTML after using icon based software
• Extra interactive features can be added
Server side and Client Side
• Server stores web pages as HTML
• Client computer downloads HTML which is interpreted by browser


Client Side Scripts
Cookies
Form Validation
Server Side Scripting
Cascading Style sheets
Style Sheets are text files with formatting rules for text in web pages
Cascading Style sheets
Current Developments
• Broadband – bandwidth increasing all the time
• 3g phones and mobile internet

Current DevelopmentsBrowsing Software
Current developments
Web Page Design
• Visual balance
(balance between text, graphics and menu bars)
• Consistency (especially with navigation)
• Emphasis
• Headers and footers
• Page layout
• Download efficiency
(not too many audio, video, flash animation linked files)

Browser Compatibility Issues
• Different versions of same browser may interpret some HTML tags differently.
• Eg tables may have different cell spacing.
• Different platforms may have different names for fonts/styles.
Download efficiency
• Web pages have to be downloaded by slow and fast connections
• Use compressed formats eg Gif, Jpeg, Mp3
• Not too many embedded audio or video clips
Uploading a Web Page
• FTP software required
• Web authoring packages contain ftp tools
• Home page must always be called index.htm