1. Internet Services

2. Today’s Goal: Internet Services To become able to appreciate the role of the Internet in today’s computing To look at several services provided by the Internet –FTP –Telnet –Web –eMail –Instant messaging –VoIP

3. Internet : the enabler !

4. What does the Internet enable ?

5. What Else? 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

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

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

8. 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

9. 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

10. inter. net

11. 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

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. Tools & Services Available on the Internet Electronic mail (POP, SMTP) Instant messaging (ICQ, MSN) Remote login (telnet) File transfer (ftp) WWW (http)

16. Chronology of events that led to today’s Internet

17. 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally connected 4 universities & enabled scientists to share info & resources across long distances ARPANET continued to expand throughout the 70's and 80's

18. 1970's Networking tools developed in the 70's include: 1972 - The National Center for Supercomputing Apps. (NCSA) develops the telnet application for remote login, making it easier to connect to a remote computer 1973 - FTP (File Transfer Protocol) is introduced, standardizing the transfer of files between networked computers

19. 1980's In 1982 and 1983, the first desktop computers begin to appear Many are equipped with an OS called Berkeley Unix, which includes networking SW, allowing easy connection to the Internet using telnet The PC revolution continues through the 80’s, making access to computer resources & net- worked info increasingly available to public

20. 1980's 1983 - The TCP/IP protocols becomes the only set of protocols used on the ARPANET This sets a standard for all networks, and generates the use of the term Internet as the net of nets

21. 1990's 1990 - The ARPANET is dissolved 1993-1994 - Web browsers Mosaic & Netscape Navigator are introduced Their GUI makes WWW & Internet more appealing to the general public

22. A lot has happened since then

23. Who runs the Internet ? Who owns it ?

24. 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

25. 203.81.197.188 www.umt.edu.pk IP address DNS address

26. 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: –203.81.197.188 (IP address of the UMT Web server)

27. ? client server

28. 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

29. 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: 203.81.197.188 www.umt.edu.pk 216.239.33.101www.google.com

30. 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

31. 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

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

33. FTP: File Transfer Protocol Used to transfer files between computers on a TCP/IP network (e.g Internet) Simple commands allow the user to: –List, change, create folders on a remote computer –Upload and download files Typical use: Transferring Web content from the developer’s PC to the Web server

34. Telnet Protocol Using Telnet, a user can remotely log on to a computer (connected to the user’s through a TCP/IP network, e.g. Internet) & have control over it like a local user, including control over running various programs In contrast, FTP allows file operations only Typical use: Configuring and testing of a remote Web server

35. 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://sst.umt.edu.pk/courses/Fall2006-7/CS101A/index.htm Before, going any further, let us dissect this URL

36. http://sst.umt.edu.pk/cs101/index.htm Protocol Identifier Server Address Directory & File Name

37. How does the Web work?

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

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

40. User’s Computer The browser breaks down the URL http://sst.umt.edu.pk/cs101/index.htm http Protocol Identifier sst.umt.edu.pk Server’s Name cs101/index.htm Directory & File Name

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

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

43. User’s Computer Web Server Browser sends a ‘GET’ request for cs101/index.htm

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

45. User’s Computer Browser displays index.htm X

46. 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

47. How does an email system work?

48. But first, the components: Email client SMTP server POP3 server

49. Email Clients Programs used for writing, sending, receiving, and displaying eMail messages Examples: Outlook, Communicator, Hotmail, YahooMail

50. SMTP: Simple Mail Transfer Protocol A protocol used to send and receive email messages over a TCP/IP network

51. POP3: Post Office Protocol A protocol used for receiving email messages A POP3 server maintains text files (one file per user account) containing all messages received by a user email client interacts with the POP3 server for discovering and downloading new email messages

52. Sender’s Computer The message is prepared using the email client Email Client

53. Sender’s Computer SMTP Server The email client sends it to the SMTP server

54. Sender’s Computer SMTP Server POP3 Server If the receiver is local, it goes to the POP3 server

55. Sender’s Computer POP3 Server The receiver picks it at his/her convenience Receiver's Computer SMTP Server

56. Sender’s Computer SMTP Server SMTP Server Internet Otherwise, it is sent to receiver's SMTP server

57. Sender’s Computer SMTP Server POP3 Server SMTP Server Which forwards it to the local POP3 server

58. Sender’s Computer SMTP Server POP3 Server SMTP Server The receiver picks it at his/her convenience Receiver's Computer

59. 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

60. Instant Messaging The IM services available on the Internet (e.g. ICQ, AIM, MSN Messenger, Yahoo! Messenger) 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

61. 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

62. Using Instant Messaging (2) The selected contact will receive that message almost immediately after you press ‘Enter’ When the contact’s IM client receives the message, it alerts the contact with a blinking message and by playing a sound

63. Using Instant Messaging (3) 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

64. How instant messaging works?

65. User launches the IM client My Computer IM Client Internet

66. IM client finds the IM server & logs in My ComputerIM Server

67. It sends communication info (IP address, etc) to the IM server My ComputerIM Server Temporary File

68. IM server finds user’s contacts & sends him/her the communication info for the ones online My ComputerIM Server

69. IM server also tells the contacts that the user is online; sends his/her communication info to them My ComputerIM Server Contact’s Computer

70. My ComputerIM Server Contact’s Computer Now the user’s & the contact’s IM clients are ready to communicate directly (P2P) The IM server doesn’t play any part in this P2P communication

71. My ComputerIM Server Contact A’s Computer As new contact’s come online, IM server informs them about the user being online & vice versa Contact B’s Computer

72. My ComputerIM Server Contact A’s Computer Multiple, simultaneous conversations are possible Contact B’s Computer

73. My ComputerIM Server Contact A’s Computer When the user logs-off, his/her IM client informs the IM server Contact B’s Computer

74. My ComputerIM Server Contact A’s Computer IM server erases the temporary file and informs the user’s contact’s about his/her ‘offline’ status Contact B’s Computer

75. 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

76. 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?

77. 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

78. 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)

79. Pro Much cheaper than traditional phone service Con Noticeably poor quality of voice as compared with land-line phone service

80. Today’s Goal: Internet Services We looked into history of Internet We looked at several services provided by the Internet –FTP –Telnet –Web –eMail –Instant messaging –VoIP We also found out about the addressing scheme used on the Internet