Using MIS 2e Chapter 6 Appendix How the Internet Works David Kroenke © Pearson Prentice Hall 2009 6A-1 Study Questions Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-2 Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-3 Q1 – How does email travel? There are many different network components involved in sending an email message across the Internet. Different types of computers, like a PC or a MAC, are used. Different types of operating systems, such as Windows, MAC OS, or Linux, are used. Different types of email application programs, such as Outlook or Mozilla Thunderbird, are used. A combination of wired and wireless connections are used. Messages are broken down into packets, or pieces of messages, that routers send in different directions. Once a message arrives at its intended destination, software programs put the pieces back together. The key concept is to divide & conquer. © Pearson Prentice Hall 2009 6A-4 Q1 – How does email travel? This figure shows how an email message may use various components to travel from one location to another. Fig 6A-1 Sample Networks © Pearson Prentice Hall 2009 6A-5 Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-6 Q2 – What is a communications protocol? A protocol is a standardized means for coordinating an activity between two or more entities. Communication protocols coordinate the activity between two or more communicating computers and allow messages to pass back and forth. © Pearson Prentice Hall 2009 6A-7 Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-8 Q3 – What are the functions of the five TCP/IP—OSI layers? The Internet uses layered protocols, also called protocol architectures. The International Organization for Standardization (ISO) developed a seven-layered Reference Model for Open Systems Interconnection (OSI) architecture. The Internet Engineering Task Force (IETF) developed a fourlayered Transmission Control Program/Internet Protocol (TCP/IP) architecture. Portions of these two architectures are combined to provide the Internet with the TCP/IP—OSI architecture. © Pearson Prentice Hall 2009 6A-9 Q3 – What are the functions of the five TCP/IP—OSI layers? This chart gives you the specific and broad functions of each layer in the TCP/IP-OSI architecture. Fig 6A-3 TCP/IP-OSI Architecture © Pearson Prentice Hall 2009 6A-10 Q3 – What are the functions of the five TCP/IP—OSI layers? Throughout this appendix, and while you’re using the Internet, you’ll hear these terms used frequently. Architecture is the arrangement of protocol layers with each given specific tasks. Protocols are sets of rules that accomplish tasks in each layer. Programs are specific computer products that implement protocols. © Pearson Prentice Hall 2009 6A-11 Q3 – What are the functions of the five TCP/IP—OSI layers? Layer 5 is the application layer and uses protocols to govern how applications work with each other. The Simple Mail Transfer Protocol (SMTP) is contained in email application programs like Outlook and Mozilla Thunderbird. The Hypertext Transfer Protocol (HTTP) is contained in Web browser programs like Internet Explorer and Mozilla Firefox. The File Transfer Protocol (FTP) is used to copy or move files from one computer to another, generally within a Web browser program. © Pearson Prentice Hall 2009 6A-12 Q3 – What are the functions of the five TCP/IP—OSI layers? Layer 4, the transport layer, contains the Transmission Control Program (TCP) protocols that convert data so different computers can communicate with each other. The TCP protocols break messages into smaller segments and provide message transmission reliability. Layer 3, the Internet layer, contains the Internet protocols (IP) that send messages across an internet using a router computer. The segments from layer 4 are put into packets and transmitted through multiple routers until they reach their intended destination. Layer 1, the physical layer, and layer 2, the data link layer, provide basic computer connectivity using switches. The packets from layer 3 are put into frames in these two layers for further transmission. © Pearson Prentice Hall 2009 6A-13 Q3 – What are the functions of the five TCP/IP—OSI layers? This figure depicts the TCP/IP—OSI layers that an email message travels through. Fig 6A-4 TCP/IP on Your Computer © Pearson Prentice Hall 2009 6A-14 Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-15 Q4 – How does the Internet work? Each computer has two addresses, a physical and a logical address, that networks and the Internet use to route messages to the correct location. The physical address or MAC, media access control, address is assigned to each NIC, network interface card, as it’s built in the factory. No two are alike. This address is used by the protocols in layer 2 of the TCP/IP—OSI architecture. The logical address, or IP address, is used on internets, the Internet, and private networks by the protocols in layers 3, 4 and 5 of the TCP/IP—OSI architecture. This address is written as numbers, like 192.168.2.28. Hardware devices are not hardcoded with logical addresses but are assigned as needed. © Pearson Prentice Hall 2009 6A-16 Q4 – How does the Internet work? There are two kinds of IP addresses: Public IP addresses are used on the Internet and are unique across all computers on the Internet. They are assigned by ICANN (Internet Corporation for Assigned Names and Numbers) Private IP addresses are used within private networks and internets and are controlled by the company that operates the network. Dynamic Host Configuration Protocols are stored on DHCP servers. The program loans temporary IP addresses to users when they connect to a network. Once the online session is completed, the IP address is returned to the DHCP server for re-use. © Pearson Prentice Hall 2009 6A-17 Q4 – How does the Internet work? This figure shows how a typical LAN transmits messages within the network using a DHCP server. Fig 6a-5 Hotel LAN in Hawaii © Pearson Prentice Hall 2009 6A-18 Q4 – How does the Internet work? Switches (special computers that receive and transmit messages on a LAN) use switch tables of data that tell them where to send traffic. They work in layer 2 of the TCP/IP—OSI architecture and use MAC addresses. Similarly, routers use routing tables that tell them where to send traffic. They work in layer 3 of the TCP/IP—OSI architecture and use IP addresses. © Pearson Prentice Hall 2009 6A-19 Q4 – How does the Internet work? You can use the figure on this slide and the next one to trace messages as they pass through the TCP/IP—OSI protocols, switches, and routers, using private IP addresses. Fig 6A-6 Accessing the (Private) Hotel Web Server – Part 1 © Pearson Prentice Hall 2009 6A-20 Q4 – How does the Internet work? Fig 6A-6 Accessing the (Private) Hotel Web Server – Part 2 © Pearson Prentice Hall 2009 6A-21 Q4 – How does the Internet work? This figure shows how TCP/IP—OSI protocols over the Internet use Network Address Translation to change a public IP address into a private IP address and vice versa. Fig 6A-7 Hawaii Hotel to Ohio Company via Internet © Pearson Prentice Hall 2009 6A-22 Q1 – How does email travel? Q2 – What is a communications protocol? Q3 – What are the functions of the five TCP/IP—OSI layers? Q4 – How does the Internet work? Q5 – How does www.prenhall.com become 165.193.123.253? © Pearson Prentice Hall 2009 6A-23 Q5 – How does www.prenhall.com become 165.193.123.253? It’s much easier for people to recognize alphabetical names rather than a group of numbers. However, computers can only use numbers. The domain name system (DNS) converts user-friendly, domain names that people can use to IP addresses that computers can use. The process is called resolving the domain name. Every domain name must be unique throughout the world. ICANN administers how other companies register domain names and it manages the domain name resolution system. The term top-level domain (TLD) refers to the last letters in a domain name. In the domain name www.prenhall.com – the last three letters, com, is the TLD. © Pearson Prentice Hall 2009 6A-24 Q5 – How does www.prenhall.com become 165.193.123.253? Each Web address is called a Uniform resource locator (URL). www.prenhall.com is the URL for Prentice Hall. Converting a domain name into a public 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. © Pearson Prentice Hall 2009 6A-25