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Lecture 13 Internet & Internet Services

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. Today’s Goal.

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Lecture 13 Internet & Internet Services

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  1. Lecture 13Internet & 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 Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones

  6. Internet Users Worldwide 673M in 20021B+ 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. 216.122.128.109www.fccollege.edu.pk DNS address IP 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. Protocol Identifier Server Address Directory & File Name http://www.fcc.edu.pk/cs/index.html

  26. How does the Web work?

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

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

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

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

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

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

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

  34. Browser displays index.html User’s Computer 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 Noticeablypoor 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?

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