Using MIS 2e Chapter 6: Data Communications Appendix: How the Internet Works David Kroenke

1. Using MIS 2e Chapter 6: Data CommunicationsAppendix: How the Internet Works David Kroenke

2. Study Questions (Chapter 6) Q1 – What is a computer network? Q2 – What are the components of a LAN? Q3 – What are the alternatives for a WAN? Q4 – How does encryption work? Q5 – What is the purpose of a firewall? Reflection Guide: Human Networks Matter More 6-2 Chapter 6/Appendix 6: Data Communications/Internet

3. A computer network is a collection of computers that communicate with one another over transmission lines. Three basic types of networks are: Local area networks (LANs) –connects computers that reside in a single geographic location on the premises of the company that operates the LAN. Wide area networks (WANs) –connects computers at different geographic sites. WAN communication lines are owned by a third-party vendor. Internet – a network of networks (the author defines an internet as a network of networks and distinguishes between internets and the Internet) The networks that comprise the Internet use a large variety of communication methods and conventions, and data must flow seamlessly across them. This is accomplished via communications protocols. Q1 – What is a computer network? 6-3 Chapter 6/Appendix 6: Data Communications/Internet

4. A local area network (LAN) is a group of computers connected together on a single company site. A switch is a special purpose computer that receives and transmits messages on a LAN. Each device on a LAN has a hardware component called a network interface card (NIC) or wireless network interface card (WNIC) connects the device’s circuitry to the cable. Each NIC (or WNIC) has a unique identifier, which is called the (MAC) media access control address. Communicating devices have two addresses: physical address (MAC) and an IP address (logical address). Devices on a LAN are connected using either Unshielded, Twisted Pair (UTP) cable or optical fiber cables Q2 – What are the components of a LAN? 6-4 Chapter 6/Appendix 6: Data Communications/Internet

5. Q2 – What are the components of a LAN? 6-5 Chapter 6/Appendix 6: Data Communications/Internet

6. Q2 – What are the components of a LAN? 6-6 Chapter 6/Appendix 6: Data Communications/Internet

7. Q2 – What are the components of a LAN? 6-7 Chapter 6/Appendix 6: Data Communications/Internet

8. WANs connect computers located at physically separated sites by obtaining connection capabilities from a third-party, typically an Internet Service Provider (ISP). The network may be created using: Leased lines from telecommunication companies; the number of lines increases dramatically as new sites are added; beneficial when high volume of traffic occurs between fixed locations Public switched network (PSDN), a network of computers and leased lines that is developed and maintained by a vendor that leases time on the network to other organizations; the organization pays for the time it uses Virtual private network (VPN) use the Internet to create the appearance of private point-to-point connections. VPN software encrypts the messages to ensure security; offers the benefit of point-to-point leased lines while enabling remote access Q3 – What are the alternatives for a WAN? 6-8 Chapter 6/Appendix 6: Data Communications/Internet

9. Q3 – What are the alternatives for a WAN (Connecting a PC)? 6-9 Chapter 6/Appendix 6: Data Communications/Internet

10. A dial-up modem uses telephone lines and a Point-to-Point Protocol (PPP) to connect a personal computer to an ISP. You dial the number for your ISP and connect The maximum speed is 56 kbps A DSL (digital subscriber line) modem operates on the same lines as voice telephones The signals do not interfere with voice telephone service. They provide much faster transmission speeds than dial up They always maintain a connection. May be symmetric or asymmetric (same or different upload and download speeds) A cable modem provides high-speed data transmission using cable television lines. Transmission speeds vary based on the number of network users A wireless modem connects to a wireless network instead of to the telephone system. When you connect with a wireless modem, you are attached directly to your wireless ISP (Internet Service Provider) Q3 – What are the alternatives for a WAN (Types of Modems)? 6-10 Chapter 6/Appendix 6: Data Communications/Internet

11. Q3 – What are the alternatives for a WAN (Leased Lines)? Organizations can use networks of leased lines from telecommunications companies to connect computers located at geographically distributed sites as this figure shows. Only predefined sites can use the leased lines. These lines provide low-cost connections if the amount of traffic warrants it. 6-11 Chapter 6/Appendix 6: Data Communications/Internet

12. Q3 – What are the alternatives for a WAN (PSDN)? A public switched data network (PSDN) is developed and maintained by a vendor who leases network time to other organizations. Each user site must lease a line on a PSDN. The line connection location is called a Point of Presence (POP). PSDNs are less costly and require less management than leased lines. 6-12 Chapter 6/Appendix 6: Data Communications/Internet

13. Q3 – What are the alternatives for a WAN (VPNs)? Virtual Private Networks (VPNs) create the appearance of private point-to-point connections by using tunnels to create virtual, private pathways over the Internet; i.e., a VPN appears to be a direct connection between two sites as shown in this figure. 6-13 Chapter 6/Appendix 6: Data Communications/Internet

14. Encryption is the process of transforming clear text into coded, unintelligible text for secure storage or communication. Consider a simple encryption scheme where each letter is transposed by a constant (known as the key) “Go Canes” becomes “Hp Dboft” (using key of 1) “Go Canes” becomes “Iq Ecpgu” (using key of 2) In this example: Only 25 keys are possible which is too limited This a symmetric key because the same key is used to encrypt and decrypt a message. Both sender and recipient must keep the key secret. In practice: Web browsers use 2128 possible keys (39-digit number) Two different keys are used to encrypt and decrypt a message (an asymmetric key). The public key is freely distributed; the private key is kept secret Q4 – How does encryption work? 6-14 Chapter 6/Appendix 6: Data Communications/Internet

15. Q4 – How does encryption work? 6-15 Chapter 6/Appendix 6: Data Communications/Internet

16. A firewall is a computing device that prevents unauthorized network access. It can be a special-purpose computer or a program on a general-purpose computer or on a router Organizations normally use multiple firewalls (next slide). Q5 – What is the purpose of a firewall? 6-16 Chapter 6/Appendix 6: Data Communications/Internet

17. A perimeter firewall sits outside the organization network; it is the first device that Internet traffic encounters. A packet-filtering firewall examines each packet and determines whether to let the packet pass. Packet-filtering firewalls can prohibit outsiders from starting a session with any user behind the firewall. They can also disallow traffic from particular sites, such as known hacker addresses. They can also prohibit traffic from legitimate, but unwanted addresses, such as competitors’ computers. Firewalls can filter outbound traffic as well. Many organizations employ internal firewalls inside the organizational network in addition to the perimeter firewall. The internal firewall protects the LAN Q5 – What is the purpose of a firewall (multiple firewalls)? 6-17 Chapter 6/Appendix 6: Data Communications/Internet

18. Reflection Guide–Human Networks Matter More 6-18 Chapter 6/Appendix 6: Data Communications/Internet

19. Study Questions (Appendix Chapter 6) Q1 – How does email travel? Ethics Guide: Sending Personal e-mail at work? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q4a – How is the Web different from the Internet? Q4b – How do you create a Web site? Q5 – How does www.prenhall.com become 165.193.123.253? 6-19 Chapter 6/Appendix 6: Data Communications/Internet

20. Q1 – How does email travel? 6-20 Chapter 6/Appendix 6: Data Communications/Internet

21. Sending/receiving personal e-mail from work generally takes only a few minutes and consumes little of the company’s resources. Is it OK to send personal e-mail? What if you send a picture (or other large file) to your friend? If you send 10 pictures to 100 friends? Where do you draw the line? What is the greater cost to the company; its resources or your time? Is there a problem? Is the activity illegal? Is the activity against company policy? Is the activity unethical? Is the activity smart? 6-21 Chapter 6/Appendix 6: Data Communications/Internet

22. A protocol is a standard means for coordinating an activity between two or more entities. A communications protocol is a means for coordinating activity between two or more communicating computers. Two machines must agree on the protocol to use, and they must follow that protocol as they send messages back and forth. An architecture is an arrangement of protocol layers in which each layer accomplishes a specific task The most commonly used architecture is comprised of five levels and is known as TCP/IP-OSI architecture. A program is product that implements a protocol Internet Explorer and Netscape are programs that implement the HTTP protocol at the top level of the TCP/IP-OSI architecture 6-22 Chapter 6/Appendix 6: Data Communications/Internet

23. Q3 – What are the functions of the five TCP/IP—OSI layers? 6-23 Chapter 6/Appendix 6: Data Communications/Internet

24. The Post Office is a good analogy of how the Internet works (Ed Krol in the Whole Internet, O’Reilly and Associates, 1992) You drop a letter into a mailbox where it is picked up with other letters and delivered to local post office The letters are sorted and sent to another post office that is closer to the destination The process is repeated until the letter is eventually picked up by the mail carrier at the other end and delivered to the local destination Each postal substation considers all of the routes available and makes the best possible decision according to the prevailing conditions All that matters is the beginning and ending address; i.e., the path may change the next time a letter is mailed Q4 – How does the Internet work (Overview)? 6-24 Chapter 6/Appendix 6: Data Communications/Internet

25. Q4 – How does the Internet work? 6-25 Chapter 6/Appendix 6: Data Communications/Internet

26. Continue the Post Office analogy, but this time we are mailing a book, not a letter. The Post Office (for whatever reason) does not accept large packages and thus we have to rip the pages out of the book and send them separately Each page is placed in its own envelope and each envelope (packet) is sent separately into the postal system Each packet may travel a different route, but all packets are assembled on the other end and then delivered This may seem complicated, but it is actually quite clever: Individual packets take turns using the connection medium so that large packages (books) do not monopolize traffic Each packet is checked for accuracy individually; if an error is found only the individual packet has to be resent All that matters is the starting and ending address; the path of individual packets may change the next time a letter is mailed Q4 – How does the Internet work (TCP/IP)? 6-26 Chapter 6/Appendix 6: Data Communications/Internet

27. Q4 – How does the Internet work (Packet Switching)? 6-27 Chapter 6/Appendix 6: Data Communications/Internet

28. HTTP (Hyper Text Transfer Protocol) the protocol that is used to transmit Web documents HTTPS – Secure protocol for confidential transactions; data is encrypted prior to being sent over the Internet HTML – The main language in which Web documents are displayed; uses codes to specify how the content should appear to the user URL (Uniform Resource Locator) – the address of a document on the Web Web Browser – A software program used to locate and display Web pages; e.g., Netscape or Internet Explorer IP address – a series of dotted decimals that identifies a unique device on a network Q4 – How does the Internet work? (Acronyms)? 6-28 Chapter 6/Appendix 6: Data Communications/Internet

29. The Internet is a network of networks Connects millions of computers in a global network where any computer can communicate with any other computer, as long as both have an Internet connection and follow Internet protocols Supports multiple protocols and applications including e-mail, news groups, instant messaging, HTTP, and FTP Originally a project of the US government and ARPANet (1969) The Web is a subset of the Internet which consists of sites that process the HTTP protocol Uses HTTP and Web browsers to access Web pages linked together by hyperlinks Created by Tim Berners Lee of CERN (1991) The Internet is about computers whereas the Web is about documents. The Web makes the Internet more interesting, but the Internet makes the Web possible Q4 – How does the Internet work? (Internet versus the Web) 6-29 Chapter 6/Appendix 6: Data Communications/Internet

30. Q4a – How do you create a Web site (Obtain a Domain Name)? 6-30 Chapter 6/Appendix 6: Data Communications/Internet

31. Once you register a domain name, you will be contacted by multiple developers seeking to create and/or host your Web site. Easiest initially to have the same company do both The cost can vary from a few hundred dollars to many thousands, depending on the nature of the site. Four distinct steps – create, host, maintain, and attract Create the site Determine the complexity of the site; the more complex, the more expensive. Complexity can go from merely displaying information, to downloading documents, to simple security (log-in), to e-commerce Navigation (depth of links; horizontal versus vertical links) Determine a visual design; a simple template is inexpensive whereas custom design adds significant Q4a – How do you create a Web site? 6-31 Chapter 6/Appendix 6: Data Communications/Internet

32. Host the site After the site is created you need a company to host the site (i.e., provide a Web server) for you. The site should be scalable; i.e., it should be built in such as way that you can simply add more servers as traffic increases Maintain the site You want control of the content (at least initially); i.e., you should be the one to add/modify content (e.g., the special of the month) Attract visitors to the site This is an entirely different issue and requires a marketing campaign in conjunction with various search engines to direct users to your site Q4a – How do you create a Web site (continued)? 6-32 Chapter 6/Appendix 6: Data Communications/Internet

33. Q5 – How does www.prenhall.com become 165.193.123.253? The domain name system (DNS) converts user-friendly names into their IP addresses. Any registered valid name is a domain name. Every domain name must be unique. A non-profit agency (ICANN, Internet Corporation for Assigned Names and Numbers) administers the registration of domain names. The top-level domain (TLD) refers to the last letters in a domain name; e.g., com, edu, and gov Converting a domain name into an IP address is called Domain Name Resolution www.prenhall.com = 165.193.123.253 Domain name resolvers are computers that store the correspondence of domain names and IP addresses. Root servers maintain lists of IP addresses of servers that resolve each type of TLD. Each Web address is called a Uniform resource locator (URL); e.g., http://www.prenhall.com is the URL for Prentice Hall. The URL may contain additional information about the document or folder where it is located; e.g., http://www.prenhall.com/kroenke 6-33 Chapter 6/Appendix 6: Data Communications/Internet

34. Q5 – How does www.prenhall.com become 165.193.123.253? (Top Level Domains 2005) 6-34 Chapter 6/Appendix 6: Data Communications/Internet

35. 6-35 Chapter 6/Appendix 6: Data Communications/Internet

36. Summary A computer network is a collection of computers that communicate with one another over transmission lines. Three types of computer networks are: LANs, WANs, and the Internet. A protocol is a set of rules for accomplishing the functions of a particular layer. An architecture is an arrangement of protocol layers; The most commonly used architecture is comprised of five levels and is known as TCP/IP-OSI architecture The Internet functions conceptually the same way as the post office; i.e., all that matters is the ending address in sending a message across the network. 6-36 Chapter 6/Appendix 6: Data Communications/Internet

37. Summary (Continued) The Web is a subset of the Internet which consists of sites that process the HTTP protocol The domain name system (DNS) converts user-friendly names into their IP addresses. You can apply for your own domain name using Register.com or a host of similar sites Four distinct tasks associated with establishing a Web site (Create, Host, Maintain, and Attract Customers) Encryption is the process of transforming clear text into coded, unintelligible text for secure storage or communication. An asymmetric approach is used with two keys, one public and one private 6-37 Chapter 6/Appendix 6: Data Communications/Internet

38. Review: Select the appropriate term for each item Subset of the Internet World Wide Web Software application used to display Web pages Browser Arrangement of protocol layers Architecture He invented the Web Berners-Lee The language of the Web HTML Special purpose computer that implements the IP protocol (the basic building block of the Internet) Router Popular protocol for LAN Ethernet Series of dotted decimals to identify a device IP Address An agreed upon format for transferring data between computers Protocol Protocol used to transmit Web documents HTTP A secure Internet protocol HTTPS 6-38 Chapter 6/Appendix 6: Data Communications/Internet