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The Internet

The Internet. Foundation Computing. Rome did not create a great empire by having meetings, they did it by killing all people who opposed them. Quiz. Why would you use slides when giving a presentation?. Quiz (2). How should a slide presentation be structured?. Quiz (3).

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The Internet

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  1. The Internet Foundation Computing Rome did not create a great empire by having meetings, they did it by killing all people who opposed them.

  2. Quiz • Why would you use slides when giving a presentation?

  3. Quiz (2) • How should a slide presentation be structured?

  4. Quiz (3) • How should a slide be designed?

  5. Quiz (4) • What are speaker notes used for?

  6. Quiz (5) • What type of content does the outline of a presentation contain?

  7. Quiz (6) • How do you group objects in presentation software?

  8. Quiz (7) • What are the characteristics of an effective presentation?

  9. Internet History • Conceived by US Department of Defense (1964) • “build a network that is sufficiently robust to withstand a nuclear attack” • ARPANET

  10. History (2) • Internetwork, or short internet, to link separate networks • No protocols for connecting different networking technologies • Common internetwork protocol, differences are hidden • TCP/IP: Transmission Control Protocol/Internet Protocol

  11. Protocols • Communication rules between two (or more) parties • Designed to solve particular internetworking problems including: • ensuring reliable transmission • routing the communication through a complex maze of computers or switches • controlling the flow of data where one communicating entity is going too fast for the other

  12. Protocols (2) • TCP/IP has three layers: • IP layer: • Responsible for getting each packet of data to its destination based on its Internet Address • does not guarantee delivery of packets • no acknowledgement sent by the IP protocol when packet is correctly delivered • Packets may get lost

  13. Protocols (3) • TCP layer • ensures that the communication is reliable • Every TCP packet is acknowledged by the receiving computer • Missing data can be retransmitted • Each end of the “conversation” can control the other if it is sending data too fast

  14. Protocols (4) • Socket layer • where internet clients (later) send information using different protocols

  15. Protocols (5) • TCP/IP independent of communications media, OS and hardware • Data split into “chunks” • Header added • Destination • Source • Service to connect to • Sequence numbers • keep packets ordered • resend lost packets

  16. Protocols (6) • Packets are very flexible – any volume, any type of payload (picture, web page, email, etc) • Packets are sent the following way • Router receives packet • If destination machine connected to this router • Deliver directly to the machine • If destination machine not connected to this router • Send it to another router • Decision where to send is made for each packet • Packets from same file can take different paths to destination

  17. Protocols (7) • Advantage: damage to part of the internet will have local effects only

  18. Internet Clients • TCP/IP allows communication between applications (clients) using their own protocols • Clients (and their protocols): • Web browsing (HTTP) • Email (SMTP – Simple Mail Transfer Protocol and POP – Post Office Protocol) • File transfer (FTP – File Transfer Protocol) • And many more…

  19. The World Wide Web • Part of the internet • Invented by Tim Berners-Lee in 1989 • A simple mechanism for sharing documents across the Internet • Key ingredients • HyperText Transfer Protocol (HTTP) • Web server • Web browser • HTML (Hypertext markup language)

  20. The World Wide Web (2) Client computer Server computer WWW browser HTTP request WWW server HTTP response HTML file

  21. The World Wide Web (3) • Every document has a Uniform Resource Locator (URL) that can be used to locate and retrieve it. • Documents in a standardised format (HyperText Markup Language or HTML) • HTML Documents can refer to other documents (hyperlinks) • Forms a "web" of documents.

  22. Browsers • retrieve and view documents on the web with browser program • browser uses hypertext transfer protocol and interprets and displays HTML documents • examples: Internet Explorer, Netscape Navigator, Mozilla Firefox • When you view a page with a browser you see the final layout, not the HTML

  23. Some Types of Websites • Personal • Educational • e-Commerce • Libraries, catalogues etc. • Search Engines

  24. Search Engines • scan the Web continuously (using a web-crawler) • websites can also be registered • build a huge data base • you can ask it to find relevant web pages by keyword • May display advertising • Google: www.google.com • Yahoo: www.yahoo.com

  25. Search Engines (2) • Search on google.com.au • Keywords • "Phrases" • AND, +, OR, NOT (-) • Website or domain (site:) • In title or URL (eg intitle: inurl:)

  26. What is a URL? • Universal Resource Locator • Components • Client protocol • Host (machine name) • Path to resource • Filename of resource http://www.sci.usq.edu.au/courses/csc1402/main.html 1 2 3 4

  27. Internet Addressing • every computer on the Internet has a numeric IP address, eg139.86.105.81 • inconvenient to remember • computers can also have a domain name, eg. www.usq.edu.au

  28. .au .gov.au .edu.au usq.edu.au sci.usq.edu.au www.sci.usq.edu.au Internet Addressing (2) • DNS (Domain Name System) maintains list of all mappings between host names and IP addresses world wide

  29. World Wide Web Consortium • Public organisation to create standards for the World Wide Web • Directed by Tim Berners-Lee • www.w3c.org

  30. Email • Client protocol for asynchronous (not at same time) messages • Requires • Sender address • Recipient address • Subject • Message • Other optional information

  31. Email (2) • Address • Unique user identifier (login) • Host (machine name) lochb@usq.edu.au 1 2

  32. Email (3) • Email vs. Webmail • Email • Client on user machine (eg Outlook) • Mail located on user machine • Mail accessed through ISP • Webmail • Accessed through Web browser (eg IE) • Mail located on webmail provider site • Mail accessed from anywhere

  33. Choosing an ISP • Check website in assignment 6 instructions for available ISPs • Some differences • Access (dialup): local (untimed) phone call or long-distance • Type of connection: dialup or broadband • Cost: connection time or download volume • Speed (upload and download) • Customer support • Modem support • Email and web space

  34. Internet Security • Encryption • Protection from attack - Firewalls • Viruses and Other Attacks • Attachments • Software • Backups • Separation • Anti-virus Software

  35. Encryption • Data transmitted on the internet can be intercepted • For privacy, communication may be encrypted (eg. credit card details) • Encryption turns plain text into encrypted text using an algorithm and a key

  36. Encryption schemes • Symmetric key (secret key) encryption: • Encryption and decryption done with same key • Key known only to sender and receiver • secure • Asymmetric key (public key) • 2 keys: public and private • Text encrypted by public key • Only receiver with private key can decode

  37. Certificates • Browsers use certificates for encryption • Used to prove that the owner of a public key is who they claim to be • Stops e.g. criminals masquerading as a legitimate e-commerce site • A trusted third party verifies that the details on the certificate are correct

  38. Firewalls • Unauthorised access to your computer from the Internet could: • "steal" information, including passwords • take control of your computer and do damage • A firewall filters all Internet traffic going into and out of your computer to ensure that it is authorised

  39. Viruses • Unwanted software that executes on your computer, possibly: • Changing settings • Doing damage, eg. deleting files • Collecting sensitive data, eg. password • Sending malicious information, eg. emails, to others

  40. Viruses (2) • Some ways in which viruses can get onto your computer: • as an attachment to an email that you inadvertently open and execute • free software downloaded that turns out to do more than you expect • active web content that is not properly authorised

  41. Viruses (3) • Don't open unknown email attachments • Download software only from reputable companies • Install anti-virus software and keep up to date • Keep backups of a "clean" system and regular updates of all your data • Separate system and personal data

  42. Spam • Not so much dangerous as annoying • Unwanted emails typically advertising something you don't want • Unwanted pop-up browser windows • Use anti-spam settings in email • Configure browser to block pop-ups • Never reply to spam email • Especially those offering to remove you from a mailing list • Example in next lecture

  43. What is a Web Cache? • Recently accessed files • Kept for future re-use • Stored in: • RAM (while browser is running) • Hard disk (between browser use) • Adjusting cache size can increase performance

  44. What is a Cookie? • Text information stored on your machine • Created by a visited site • Sent to that site (only) with later requests for resources

  45. Is My Browser Secure? • Look for the padlock • Transmissions between host and client encrypted

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