The Internet. Chapter 10. Learning Objectives. Chapter Outline. After reading this chapter, you should be able to:

Transcription

1 The Internet Chapter 10 Learning Objectives After reading this chapter, you should be able to: Discuss the responsibilities of the Internet Protocol (IP) and how IP can be used to create a connection between networks Discuss the responsibilities of the Transmission Control Protocol (TCP) and how it can be used to create a reliable end-to-end network connection Identify the relationships between TCP/IP and the protocols ICMP, UDP, ARP, DHCP, NAT, and tunneling protocols Cite the basic features of HTML, Dynamic HTML, and XML and describe how they differ from each other Describe the responsibility of the Domain Name Service and how it converts a URL into a dotted decimal IP address Describe the major Internet applications and services Discuss the business advantages of the World Wide Web Recognize that the Internet is constantly evolving and that IPv6 and Internet2 demonstrate that evolution Chapter Outline 1. Introduction 2. Internet Protocols a. The Internet Protocol (IP) b. The Transmission Control Protocol (TCP) c. Internet Control Message Protocol (ICMP) d. User Datagram Protocol (UDP) e. Address Resolution Protocol (ARP) f. Dynamic Host Configuration Protocol (DHCP) g. Network Address Translation (NAT) h. Tunneling protocols and virtual private networks (VPNs) 3. The World Wide Web a. Locating a document on the Internet b. Creating Web pages

2 4. Internet Services a. Electronic mail ( ) b. File Transfer Protocol (FTP) c. Remote login (Telnet) d. Voice over IP (Internet telephony) e. Listservs f. Streaming audio and video g. Instant messaging 5. The Internet and Business a. Cookies and state information b. Intranets and extranets 6. The Future of the Internet a. Ipv6 b. Internet2 7. The Internet In Action: A Company Creates a VPN 8. Summary Lecture Notes Introduction Many people think the Internet is only the service that allows a person to browse Web pages and click links, but it is actually much more. One of the first services, and still one of the more popular offered on the Internet, is the File Transfer Protocol (FTP), which allows a user to upload or download files. Other services offered by the Internet include remote login, Internet telephony, electronic mail, listservs, voice over IP, and streaming audio and video. To support the Internet, a host of protocols is necessary. Two of the most common protocols are the Internet Protocol (IP) and the Transmission Control Protocol (TCP). These protocols are supported by a host of secondary protocols, which include Internet Control Message Protocol (ICMP), User Datagram Protocol (UDP), and Address Recognition Protocol (ARP). Internet Protocols Although many protocols are necessary to support the operation of the Internet, several stand out as the most common: Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Internet Control Message Protocol (ICMP), and Address Resolution Protocol (ARP). The reliable transport service, provided by software called Transmission Control Protocol (TCP), turns an unreliable sub-network into a reliable network, free from lost and duplicate packets. If an application did not need to create a connection to transfer data, the User Datagram Protocol (UDP) could be used instead of TCP. UDP supports a connectionless application in which a connection-oriented stream of packets is not necessary. The

3 connectionless packet delivery service provides an unreliable, connectionless network service in which packets may be lost, duplicated, delayed, or delivered out of order. Even worse, the sender and receiver of these packets may not be informed that these problems have occurred. This connectionless packet delivery service is called Internet Protocol (IP). Because the connectionless packet delivery service doesn t inform users that problems may have occurred, a reliable transport service is needed above the connectionless packet delivery service to cover for its possible shortcomings. The World Wide Web Although the Internet still offers tried-and-true services, such as file transfer, electronic mail, and remote login, a relatively new service has grown dramatically since its introduction in 1992: the World Wide Web (WWW). Using a Web browser such as Netscape Navigator or Microsoft Internet Explorer, you can download and view Web pages on a personal computer. Of all the Internet services, the World Wide Web has probably had the most profound impact on business. Web pages are created using Hypertext Markup Language (HTML) generated manually with a text-based editor such as Notepad or by using a Web page authoring tool. Once a Web page is created, it is stored on a computer that contains Web server software and has a connection to the Internet. The Web server software accepts Hypertext Transport Protocol (HTTP) requests from Web browsers connected to the Internet, retrieves the requested Web page from storage, and returns that Web page to the requesting computer via the Internet. Although HTML is the original and still most commonly used method for controlling the display of Web pages, two new forms of HTML have emerged that offer more power and flexibility in Web page creation: dynamic HTML and extensible Markup Language. Internet Services When the Internet came into existence as the Arpanet, most people used the Internet for , file transfers, and remote logins. To appreciate the many capabilities of the Internet, let s examine several of the more popular services that the Internet provides today, starting with File Transfer Protocol for downloading and uploading files and continuing with remote login, Internet telephony, , listservs, voice over IP, and streaming audio and video. The Internet and Business An intranet is a TCP/IP network inside a company that allows employees to access the company s information resources through an Internet-like interface. Using a Web browser on a workstation, an employee can perform browsing operations, but the applications that can be accessed through the browser are available only to employees within the company. When an intranet is extended outside the corporate walls to include suppliers, customers, or other external agents, the intranet becomes an extranet. Since an extranet allows external agents to have access to corporate computing resources, a much higher level of security is usually established.

4 The Future of the Internet The Internet is not a static entity; it continues to grow by adding new networks and new users every day. People are constantly working on updating and revising the Internet s myriad pieces. One of the biggest changes to affect the Internet will be the adoption of a new version of the Internet Protocol, IPv6. Currently, most of the Internet is using IPv4, which was the version presented earlier in the chapter. If changes to the IP protocol are not enough, work is progressing on a new, very high-speed network that will cover the U.S., interconnecting universities and research centers at transmission rates up to a gigabit per second (1000 Mbps). The new highspeed network is called Internet2, and its links are currently being built and tested on top of existing Internet links. The Internet In Action: A Company Creates a VPN The In Action example for this chapter shows how a company can support its external and mobile employees by providing them with a virtual private network (VPN). This VPN uses the Internet along with additional protocols that support secure connections from anywhere into the corporate system. Quick Quiz 1. What is the relationship between the Internet and World Wide Web? The World Wide Web is one service of many offered by the Internet. 2. What is the relationship between HTTP and HTML? HTTP is the protocol to transfer Web pages and HTML is the scripting language that displays Web pages. 3. What are the principal functions of TCP and IP? TCP provides an error-free end-to-end connection, while IP provides a connectionless network packet transfer service. Discussion Topics 1. Is IP fragmentation a thing of the past? 2. Are cookies an invasion of privacy? 3. With the flurry of viruses that are passed in attachments, will the attachments such as Word files and Excel files become outlawed?

5 4. The hackers that perform distributed denial-of-service attacks on e-commerce sites: are they criminals or are they heroes helping computer specialists discover faults within computer networks and systems? Teaching Tips 1. Emphasize that the Internet offers many services and not just the World Wide Web. 2. Suggest that students seek out and join a listserv of their choice. Make sure they save the information necessary to unsubscribe at a later date. 3. It is probably not necessary to discuss each of the fields in the IP and TCP headers. You may only want to introduce the few that are relevant to the discussion. 4. Tunneling protocols and virtual private networks are very popular. Make sure you discuss these terms with an example or two. 5. You might want to discuss the current status of IPv6 and/or Internet2. Solutions to Review Questions 1. What was the precursor to the present day Internet? Arpanet first, then NSFnet 2. List the main responsibilities of the Internet Protocol. To transfer data packets across the Internet 3. List the main responsibilities of the Transmission Control Protocol. To create an error-free end-to-end connection over the Internet 4. Explain the relationship of the port to an IP address. An IP address identifies a computer s connection to the Internet, while a port address identifies a particular application on that computer. 5. Is UDP the same thing as TCP? UDP creates an error-free connectionless connection, while TCP creates an error-free connection-oriented connection.

6 6. What is the purpose of MPLS? To speed packets through routers 7. What is the relationship between IP and ICMP? ICMP returns an error message to the sender when an error happens during IP. 8. Is DHCP the same thing as NAT? Explain. No. DHCP dynamically assigns IP addresses to machines that need them, while NAT can substitute an IP address when the packet leaves the user s premises. 9. What is the relationship between the Internet and the World Wide Web? The World Wide Web is one service of the Internet. 10. What is the HTTP protocol used for? It is used to transfer Web pages across the Internet. 11. How is a Web markup language different than a programming language? Much simpler, relatively English-like, does not require loops or decisions 12. What features have been added to HTML to produce dynamic HTML? Pop-up responses, layering, cascading style sheets, and better data binding 13. What can a cascading style sheet add to a Web page? Uniformity by creating one style sheet (or a series of style sheets) for multiple documents. 14. How does XML differ from HTML and dynamic HTML? XML also defines the data that is transferred with the Web page. 15. What is the purpose of the uniform resource locator (URL)? To identify every document on the Internet 16. List the four basic parts of the URL. Service, host name, directory info, filename

7 17. How does the domain name server translate a URL into a 32-bit binary address? DNS uses a distributed database system of URL address. 18. What are the different classes of IP addresses? Classes A through D (using classful addressing) 19. What is the File Transfer Protocol (FTP) used for? It is used to download and upload files across the Internet. 20. What is the main function of Telnet? To allow a remote user to log in to a computer system via the Internet 21. Is VoIP more reliable within a business or over the Internet? Explain. More reliable within a business (better throughput) 22. What other options are available for transmitting voice via Internet technology besides voice over Internet? Voice over frame relay and voice over ATM 23. List the basic features of a common electronic mail system. Send, receive, archive messages; group mailings; listservs 24. What are the duties of SMTP, POP3, and IMAP when referring to systems? SMPT is used to transfer an , and POP3 and IMAP are used to hold and later access messages. 25. What is a listserv used for? It is used to support an -based discussion group on a particular subject of interest. 26. What tools are necessary to support streaming audio or video? A real-time streaming protocol and a software viewer 27. How does Instant Messaging differ from ? It is instant and usually only one or two lines of data.

8 28. What are the two competing protocols used to support Instant Messaging? This is not covered in the text, but here is what Wikipedia has to say: There have been several attempts to create a unified standard for instant messaging: IETF's SIP (Session Initiation Protocol) and SIMPLE (SIP for Instant Messaging and Presence Leverage), APEX (Application Exchange), Prim (Presence and Instant Messaging Protocol), the open XMLbased XMPP (Extensible Messaging and Presence Protocol), more commonly known as Jabber and OMA's (Open Mobile Alliance) IMPS (Instant Messaging and Presence Service) created specifically for mobile devices. 29. What is the relationship between Electronic Data Interchange and e-commerce? EDI is one facet of e-commerce. 30. What is a cookie? Who makes cookies and where are they stored? A cookie is a small set of data stored on a user s computer. Created by a Web server, cookies are stored in a file or files on the computer s hard disk. 31. How do intranets and extranets compare and differ from the Internet? An intranet is an internal Internet that is usually only open to employees of a company. An extranet is an interconnection of intranets. 32. How can a business use a private virtual network and tunneling to support an offsite connection? They allow a remote user to create a secure connection across the Internet into the user s corporate computing system. 33. How will IPv6 differ from the current version (4) of IP? Smaller, simpler header; bigger IP addresses; better security; quality of service added 34. What are the main features of Internet2? High speed, high bandwidth for computationally intensive applications Suggested Solutions to Exercises 1. Does the U.S. government support the Internet? Explain. No, it no longer directly supports the Internet. Private industry and universities now support the many facets of the Internet.

9 2. Given an IP packet of size 540 bytes and a maximum packet size of 200 bytes, what are the IP Fragment Offsets and More flags for the appropriate packet fragments? First fragment: Offset=0, More flag=true Second fragment: Offset=25, More flag=true Third fragment: Offset=50, More flag=false 3. The Hop Limit field in IP version 6 is 8 bits long (the same size as the equivalent Time to Live field in IPv4). Since this hop count is decremented each time an IP datagram enters a router, what are the implications of such a small field size? A packet cannot hop through as many routers. 4. In your town there is a small commercial retail building with essentially one room. On one side of the room is a real estate agency and on the other side of the room is a guy who sells tea. What is the relationship between this setup and the concept of IP addresses with TCP port numbers? You could think of the building as having one postal address (IP address) with two operations within the building (two port addresses). 5. Somewhere in the middle of the United States are two Internet routers with routing tables that are all messed up. The two routers keep sending their packets back and forth to each other, nonstop. Will an error message ever be generated from this action? If so, who will generate the error message and what might it look like? Eventually each packet s Time to Live field should expire, causing the packet to be discarded and ICMP to send a message back to the source that generated the packet. 6. Why is ARP necessary if every workstation connected to the Internet has a unique IP address? Because once a packet arrives at the destination local area network (such as a CSMA/CD LAN), the LAN protocol does not look at IP addresses but uses the MAC layer addresses to deliver the frame. 7. If I dial in to the Internet from home, is it likely that my workstation is using DHCP? Explain. Yes, very likely. It s much easier to assign an IP address dynamically than to give every potential user an IP address. 8. If someone on the Internet sends you an , will NAT delete it before it gets delivered to you? Why or why not?

10 No, because even though a user on the inside did not request the incoming packet, the NAT server will recognize that the packet is intended for the local server. 9. If three users on one local area network all request a Web page at the same time, how does NAT know which results go to which workstation? The NAT software records each outgoing request so that when the Web pages come back, it knows which Web page goes to which workstation. 10. If your computer workstation has an IP address of , is it a Class A, B, C, or D IP address? It is a Class C address. 11. What are the advantages and disadvantages of using dynamic IP address assignments? Advantages: A company can purchase fewer IP addresses since each machine will not be statically assigned a fixed address but dynamically assigned an address when it accesses the Internet. Disadvantages: The software is more elaborate; what if 100 IP addresses are purchased and the 101st user tries to access the Internet? 12. Locate and label the service, host name, directory, and filename in the following URL: Service: Host name: Directory: /listings/pages/ Filename: web.htm 13. Using a Web browser, go to site and list three of the subdirectories in the directory pub. 14. If you use your computer primarily for Telnet into a remote computer, will you have a large long-distance telephone bill? No. Telnet allows you to log in to a remote computer system by placing a (hopefully) local call to your Internet service provider. 15. What is the difference between voice over the Internet and private VoIP? Private VoIP exists only within a corporate network and may never access the outside Internet. 16. Convert the telephone number into ENUM form e164.arpa

11 17. With respect to , what is the relationship between SMTP and POP3? Can one operate without the other? SMTP transmits the messages, while POP3 holds the messages and displays them when you log on. You really need both for an system to work. 18. Your company has asked you to keep abreast of workplace ethics. Which Internet service(s) introduced in this chapter would best help you accomplish this task? You might consider a listserv for workplace ethics. If there is none, the World Wide Web would also be a good resource. 19. Are HTTP and HTML two protocols with the same function? Explain. No. HTTP transmits Web pages and HTML displays them. 20. Given the following section of HTML code, what will be displayed on the screen when the HTML code is read by a browser: <HTML> <BODY> <H1> Chapter Eleven </H1> <HR> <IMG SRC= amerflag.gif ALIGN=RIGHT> <A HREF= > Everyone College Home Page </A> </BODY> </HTML> 21. Which dynamic HTML concept will print the phrase Computer Network multiple times on the screen, each one larger than the previous one and each one slightly overlapping the previous one? Layers 22. Is HTML a subset of XML, or is it the other way around? Explain. HTML is a subset of XML. In XML, you can define any tag you wish, including the tags normally used in HTML. 23. Some of the new protocols, such as Internet Protocol version 6, are not including any kind of error detection scheme on the data portion of the packet. What significance does this trend indicate? To some degree, the protocols are relying on the better transmission qualities of modern media, such as fiber-optic cable. Also, the protocols are relying on higher-layer protocols to take care of error detection and correction.

12 Thinking Outside the Box 1. You are working for a company that wants to begin electronic data interchange (EDI) with two other companies that supply parts. Your company produces mobile telephones, and the two other companies produce batteries and telephone keypads. When your company places an order with the battery company, it specifies battery size, battery type, battery power, and quantity. When your company places an order with the keypad company, it specifies keypad configuration, power consumption, keypad dimensions, and keypad color. How might XML be used to support EDI between these companies? XML can be used to define the data structure (battery size, battery type, battery power, quantity) that is part of the purchase order. 2. Two banks want to establish an electronic link between themselves, over which they can transmit money transfers. Can they use a virtual private network and a tunneling protocol, or is a better technique available? Defend your answer. A VPN would be a good solution, as long as a high level of security is implemented. A leased telephone service with encryption will also work. 4. You are thinking about creating a network solution for a small business of approximately 10 users. You give each user a workstation and access to the Internet. Which Internet protocols will your network and workstations need to support? Which optional IP protocols might you implement? TCP, IP, and ARP are necessary. NAT and DHCP might be very useful too. 5. A company currently has a telephone system and a separate system of local area networks. It is thinking about converting its telephone system to VoIP and running both voice and data over the system of local area networks. What must the company consider before making this move? Can the company s current network support the much higher load of voice over IP? If not, what has to be installed? How much will this upgrade cost?