Lecture 3

1. Lecture 3 The Internet: technology and services

2. Internet Technologies

3. The UNIX Connection • The Internet has grown out of UNIX Operating System • Some Internet terms (email address) and services (FTP) become more clear after we cover UNIX

4. The Internet: A Network of Networks The Internet is an interconnected network of thousands of networks linking academic, research, government, and commercial institutions.

5. Networks Near and Far • There are two general types of computer networks: • LAN(Local Area Network) • WAN(Wide Area Network)

6. LAN (Local Area Network) • A LAN is a network in which the computers are physically close to each other • LAN networks are usually set up to share peripherals, such as printers and network servers • Each computer andshared peripheral isa node on the LAN

7. WAN (Wide Area Network) • A WAN is a network in which the computers are a great distance from one another • Connections are madevia telephone lines, satellites, and/ormicrowave relay towers • Each network site is anode

8. WAN (Wide Area Network) • WANs are often made up of LANs

9. Communication á la Modem • A modem is needed to connect a computer to a phone line • The computercommunicateswith digital signals • The telephone systemwas designed to transmit voice signals which are analog

10. Client/Server Model

11. Internet Protocols TCP/IP (Transmission Control Protocol/Internet Protocol) is the protocol at the heart of the Internet.

12. Internet Protocols • TCP/IP translates into: • TCP (transmission control protocol) breaks messages into packets. • IP (Internet protocol) is the addressing for the packets. • computer in the Internet (host) is identified by IP address (e.g. 128.214.9.225) • IP addresses run out

13. Internet Addresses An Internet address is made up of two parts separated by the @ symbol: • the person’s user name • the host name The host is named using DNS (domain name system), which translates IP addresses into a string of names.

14. Internet Addresses An Internet address includes: username@hostname.sub.dom username is the person’s “mailbox” hostname is the name of the host computer and is followed by one or more domains separated by periods: • host.subdomain.domain • host.domain • www.cs.helsinki.fi • gurtov@cs.helsinki.fi (Andrei.Gurtov@Helsinki.FI alias)

15. Internet Addresses Top level domains include: • .edu - educational sites • .com - commercial sites • .gov - government sites • .mil - military sites • .net - network administration sites • .org - nonprofit organizations

16. Intranets • Intranets – internal closed networks of organizations that are designed using the same technology as the Internet. • Firewalls - used to prevent unauthorized communication and secure sensitive internal data. • Virtual Private Networking (VPN) -- a way to access intranets from public Internet

17. Internet Services

18. The World Wide Web:Browsing the Web WWW is a distributed browsing and searching systems developed by CERN. Use hypertext links and navigational aids to explore information on the Internet.

19. Web Addresses URL (Uniform Resource Locator): addresses for the World Wide Web. http (hypertext transfer protocol): the protocol of the WWW

20. Searching the Web • A directory (also an index) is a hierarchical catalog of Web sites compiled by researchers.

21. Searching the Web • A search engine offers a more complete database of what is one the WWW. A software robot or spider retrieves the entries according to key word queries.

22. Email on the Internet • Email (one-on-one communication). • Pine - UNIX-based mail program. • MIME - Multipurpose Internet Mail Exchange - allows you exchange files through email. Outlook express and Netscape provide more advanced mail readers

23. Disadvantages of Email • Works only if the recipient responds • Authentication is not ensured • Email is not private • Can be overwhelming (SPAM) • Both filter out manyhuman componentsof communication

24. Mailing Lists and Newsgroups • Email is a valuable tool for one-to-one communication • Mailing lists allow you to participate in email discussion groups on special-interest topics. • Usenet Newsgroups are virtual bulletin boards that you access with a news reader

25. Example of a mailing list FOREIGN-STUDENTS@HELSINKI.FI is an email list meant for distributing information among foreign students at the University of Helsinki. Instructions on how to USE and LEAVE the mailing list are available at the ESN website:http://www.helsinki.fi/hyy/esn/eng/lists.html Before posting mail to the mailing list, be sure that you have read the NETIQUETTE of this list:http://www.helsinki.fi/hyy/esn/eng/misc/fs_netiquette.html

26. Mailing list (cont) To subscribe mail majordomo@helsinki.fi in message body subscribe foreign-students To unsubscribe mail majordomo@helsinki.fi in message body unsubscribe foreign-students Remember, the machine is stupid so write exactly as above and try several times if it fails Never send these requests to the mailing list itself

27. Mailing list (cont) Contact the list administrator with related problems at foreign-students-owner@helsinki.fi Do not start or participate in flaming • I.e. making offensive comments about the person, spelling mistakes, etc. • If you do, the administrator can remove you from the list

28. Other email features • Attachments (one MB files are ok) • Filters • Ignore sender • Group by conversation • Work offline • Encryption and signature

29. News groups • News (BBS) and web forums are an alternative for mailing lists • Most news groups maintain Frequently Asked Questions (FAQ) • Read FAQ before posting questions • Web browsers like Netscape and IE have tools for reading news

30. Remote Access and File Transfer The most popular use of the Internet is information discovery and retrieval. Because the Internet is unorganized, you can use the following tools: Telnet: for remote login to other computers. FTP: file transfer protocol; transfer files from remote computers. SSH: secure remote login and file transfer

31. Paging and chatting Talk is a UNIX program that allows you to carry on a split-screen communication Internet relay chat (IRC) allows several users to type simultaneously ICQ (I seek you): user-friendly messaging system • Microsoft Messenger is a similar tool

32. Streaming • Listen to music from live radio stations • Using RealPlayer or Microsoft Media Player • E.g. www.yle.fi provides links to several life stations • You can even find live air traffic control • Pilots talking to a dispatcher

33. File sharing • Search and download files like latest hits (mp3), blockbuster movies (mpeg), latest software packages (zip),pictures... • Make your own files available to others • Tools like Gnutella or Napster • Difficult for authorities to snap these systems to their distributed nature

34. Real-Time Communication Video telephony (see, hear, and type to another person). • MBONE - Multicast Backbone – centralized distribution • NetMeeting – works over ”off-the-shelf” Internet

35. E-Commerce • Users connect (usually for a fee) to a variety of on-line databases • On-line databases include: • current stock market status • digital libraries • banking • shopping

36. Online banking • Provided in Finland by all major banks • E.g. in Leonia costs less than any other service package • You get a customer number and a PIN code to log-in at their web site • You get a challenge-response table of codes • All connections are encrypted • Within the same bank money are moved instantly, otherwise it takes a couple of days

37. Rules of Thumb: On-line Survival Tips • Protect your privacy • Cross-check on-lineinformation sources • Netiquette • Avoid informationoverload