1. Lecture 13 Internet & Internet Services CSCS100 - Spring 2008 – Forman Christian College Asher Imtiaz Wajeeha Akram *Several of these slides have been adapted and modified from VU CS101 slides (Dr. Altaf A. Khan) and Peter Norton’s supplementary material.

2. Today’s Goal Internet Architecture Addressing scheme used on the Internet To look at several services provided by the Internet Web eMail Instant messaging VoIP

3. What Does the Internet Enable? Enables users located at far-way locations to easily share information with others located all over the world Enables users to easily and inexpensively communicate with others located all over the world Enables the users to operate and run programs on computers located all over the world

4. The Internet is unlike any previous human invention. It is a world- wide resource, accessible to all of the humankind.

5. “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Internet phones

6. Internet Users Worldwide 673M in 2002 1B+ in 2005 (48% wireless)

7. Key Characteristics (1) Geographic Distribution Global - reaches around the world Robust Architecture Adapts to damage and error Speed Data can travels at near ‘c’ on copper, fiber, airwaves

8. Key Characteristics (2) Universal Access Same functionality to everyone Growth Rate The fastest growing technology ever Freedom of Speech Promotes freedom of speech The Digital Advantage Is digital: can correct errors

9. Internet: Network of Networks A large number of networks, interconnected physically Capable of communicating and sharing data with each other From the user’s point view, Internet – a collection of interconnected networks – looks like a single, unified network

10. Internet ---- Web ?

11. Internet ---- Intranet ?

12. Internet Networking Protocols Communications on the Internet is controlled by a set of two protocols: TCP and IP

13. TCP/IP (1) Transmission Control Protocol/Internet Protocol Networking protocol used by all computers and networks on the Internet Originally developed by the US DoD for Unix, but now available for most other OSes

14. TCP/IP (2) Transmission Control Protocol/Internet Protocol TCP breaks down the message to be sent over the Internet into packets IP routes these packets through the Internet to get them to their destination When the packets reach the destination computer, TCP reassembles them into the original message

15. Internet Addressing Regular post cannot be delivered unless we write a destination address on the envelope Same is true for the Internet Regular post can be delivered at the intended address even if the given address is not precise. That is not the case for Internet addressing

16. 216.122.128.109 www.fccollege.edu.pk IP address DNS address

17. IP Address (1) A unique identifier for a computer on a TCP/IP network Format: four 8-bit numbers separated by periods. Each 8-bit number can be 0 to 255 Example: 216.122.128.109 (IP address of the FCC Web server)

18. IP Address (2) Networks using TCP/IP route messages based on the IP address of the destination Any IP addresses (as long as they are unique) can be assigned within a PN However, connecting a PN to the Internet requires using unique, registered IP addresses

19. Domain Names IP addresses are fine for computers, but difficult to recognize and remember for humans A domain name is a meaningful, easy-to- remember ‘label’ for an IP address Examples: 216.122.128.109 www.fccollege.edu.pk 216.239.33.101 www.google.com

20. DNS: Domain Name System (1) DNS is the way that Internet domain names are located & translated into IP addresses Maintaining a single, central table of domain name/IP address relationships is impractical Billions of DNS-IP translations take place every day The DNS-IP tables get updated continuously

21. DNS: Domain Name System (2) Tables of DNs & IP addresses are distributed throughout the Internet on numerous servers There is a DNS server at most ISPs. It converts the domain names in our Internet requests to actual IP addresses In case it does not have a particular domain name in its table, it makes a request to another DNS server on the Internet

22. TCP/IP Settings in a Computer

23. Internet Services There are many, but we will look at only the following: Web eMail Instant messaging VoIP

24. The Web The greatest, shared resource of information created by humankind A user may access any item on the Web through a URL, e.g. http://www.fccollege.edu.pk/cs/index.html Before, going any further, let us dissect this URL

25. http://www.fcc.edu.pk/cs/index.html Protocol Identifier Server Address Directory & File Name

26. How does the Web work?

27. User’s Computer User launches the browser on his/her computer Browser

28. User’s Computer User types in the URL into the browser

29. User’s Computer The browser breaks down the URL http://www.fcc.edu.pk/cs/index.html http Protocol Identifier www.fcc.edu.pk Server’s Name cs/index.html Directory & File Name

30. User’s Computer DNS Server Browser sends server’s name to the DNS server Domain Name IP Address

31. User’s Computer Web Server Internet Browser establishes a connection with the server

32. User’s Computer Web Server Browser sends a ‘GET’ request for cs/index.html

33. User’s Computer Web Server Server sends the requested file to the browser

34. User’s Computer Browser displays index.html X

35. eMail Computer-to-computer messaging Inexpensive, and quite quick, but not instant! The most popular service on the Internet, even more than surfing, but soon to be overtaken by instant messaging Billions are sent every day

36. The Trouble with eMail Slow response times No way of knowing if the person we are sending eMail to is there to read it The process of having a conversation through eMail by exchanging several short messages is too cumbersome Instant messaging (IM) solves these problems

37. Instant Messaging The IM services available on the Internet (e.g. ICQ, GoogleTalk, MSN Messenger, Yahoo! Messenger and Skype) allow us to maintain a list of people (contacts) that we interact with regularly We can send an instant messages to any of the contacts in our list as long as that contact is online

38. Using Instant Messaging (1) Whenever a contact in our list comes online, the IM client informs us through an alert message and by playing a sound To send an instant message to a contact, just click on the contact in the IM client, and start typing the message The selected contact will receive that message almost immediately after you press ‘Enter’

39. Using Instant Messaging (2) When the contact’s IM client receives the message, it alerts the contact with a blinking message and by playing a sound That contact then can type a response to the received message, and send it instantly Several such conversations can be carried out simultaneously, each occupying a separate IM windows

40. Key Point Once the IM server provides the communication info to the user and his/her contact’s IM client, the two are able to communicate with each other without the IM server’s assistance This server-less connection is termed as a P2P connection

41. Question Why do we require the server in the first place? Why doesn’t my IM client look for the user’s contact’s IM client without the IM server’s help?

42. Answer Many users (including almost all home users) do not have permanent IP addresses. They are assigned temporary IP addresses by their ISP each time they connect to the Internet The server-based IM scheme removes the need of having permanent IP numbers It also gives IM users true mobility, allowing them the use of IM from any Internet- connected computer

43. VoIP: Voice over IP Voice delivered from one device to another using the Internet Protocol Voice is first converted into a digital form, is broken down into packets, and then transmitted over a TCP/IP network (e.g. Internet) Four modes: C2C C2T T2C T2T (with a TCP/IP net somewhere in between)

44. Pro Much cheaper than traditional phone service Con Noticeably poor quality of voice as compared with land-line phone service, but not much worse than cell phone service

45. Who runs the Internet ? Who owns it ?