Chapter 3

1. Chapter 3 Internet

2. Physical Components of the Internet • Servers • Networks • Routers

3. Server • Computer • Answers requests for services. • Mail servers • Web servers • List servers (discussed in Ch. 10) • News servers (discussed in Ch. 10)

4. Network • A computer system that uses communications equipment to connect two or more computers and their resources. • Actual physical means for transporting data (packets of information)

5. Network • Uses: • Copper wires -- electrical impulses. or • Fiber-optic cables - light waves. or • Radio Waves or • Microwaves or • Infrared light -- invisible light that carries a message through air.

6. Router • Special-purpose computer • Computer that directs data packets along the network.

7. Local Area Network (LAN) • A network designed to share data and resources among several computers, usually personal computers in a limited geographical area, such as an office or a building. (compare to WAN)

8. Wide Area Network (WAN) • A network of geographically distant computers and terminals. (compare to LAN)

9. Host • The central computer in a network, to which other computers, and perhaps terminals, are attached. • A personal computer with file-transfer software permits a user to download data files from the host or upload data files to the host.

10. Downloading a file means to retrieve it from another computer.

11. Uploading a file means to send a file to another computer.

12. Node • A device, usually a personal computer, that is connected to a network.

13. Star network topology Hub Computer

14. Ring network topology Computers are connected in a circular fashion

15. Bus network topology Network is preserved if one computer fails

16. Benefits of a Network • Used as a back up for files • Resources, such as printers, can be shared • Promotes an ease of communication through e-mail, transferring files and videoconferencing

17. Benefits of a Network (continued) • It costs less to use several small computers connected to a network than to use a large computer. • And several small computers connected to a network can offer more computing power than just using a single large computer.

18. Packet switching • Transmitted data is divided into small packets of information. • Each packet has the same destination but does not necessarily take the same path.

19. Advantages of packets • Packets can be rerouted to a less congested area of the network if a particular area is congested. • If the network experiences a failure, packets can be rerouted. • If a packet is corrupted, only the corrupted packet needs to be resent.

20. What other information is contained in a packet? • Info about the computer that sent it • Info about the computer to which it is being sent • A sequence number

21. TCP / IP • Software managing the transmission of the individual packets. • TCP / IP - Transmission Control Protocol / Internet Protocol • Consists of many (approx. 100) different protocols • Communication between networks is based on the TCP/IP suite.

22. TCP • Places the data into packets and reassembles the packets.

23. IP • Handles the addressing and sees to it that packets are routed across multiple computers.

24. Connecting to the Internet • User connects to the ISP (Internet Service Provider) using either a modem or an ISDN (Integrated Services Digital Network) • Replaces a modem with a special adaptor. • ISP connects to the NSP (Network Service Provider) networks through leased lines through the local phone company. • TCP/IP then divides the message into packets and sends them over the lines.

25. Connecting to the Internet (continued) • The router directs the packets to their destination. • The packets are reassembled at their destination-computer which then responds to any request. • A message is sent from the destination computer to the sending computer in order to request that any missing or corrupt packets be resent.

26. Internet • Network of networks • Used to: • View web pages (WWW) • Download files (ftp) • Files located on a remote computer can be downloaded • Communicate through e-mail

27. Internet (another definition) • Global information system linked together by a unique address space (DNS).

28. Domain Name System (DNS) • Used to assign names to host computers.

29. Domain Name • Symbolic name used to identify each computer on the Internet.

30. IP Address • Numeric name used to identify each computer on the Internet. • Consists of 32 bits (4 bytes)

31. Largest 8 bit number is 255. Smallest 8 bit number is 0 11111111 = 28 - 1 = 255 00000000 = 0

32. IP Address (continued) • Consists of a network component and a host component. • Ex. 102.150.8.68 • 01100110 = 102 • 10010110 = 150 • 00001000 = 8 • 01000100 = 68

33. Review • URL entered • http://publications.UNL.edu/faculty/index.htm • Browser queries the DNS for the IP Address • Domain Name System • IP address returned • 123.66.102.77

34. TCP connection is established with 123.66.102.77 • Browser then asks for the “what” part of the URL • index.htm • The server, publications.UNL.edu, sends back the file index.htm.

35. TCP connection is then closed • Browser renders the text portion of the HTML code contained in index.htm • Steps are repeated in order to retrieve any in-line images within index.htm. • In-line image -- Image within a document.

36. Who can publish on the web? • Anyone

37. Some material is monitored for accuracy. • Electronic Journals • Commercial presentations • Reputable authors

38. Be a critical judge • Who wrote it? • Is the writing quality high? • Is the document up to date? • Are there obvious errors?

39. Note: Pg. 126 Communication Mechanisms LOL - laughing out loud TY - thank you RTFM - Read The Fine Manual • Not all substitute the word “fine” for the letter “F”.