1. Chapter Extension 7 How the Internet Works © 2008 Prentice Hall, Experiencing MIS, David Kroenke

2. CE 7-2 Study Questions How does e-mail travel? What is a communications protocol? What are the functions of the five TCP/IP OSI layers? How does the Internet work? How does www.PrenHall.com become 192.52.0.34.65?www.PrenHall.com

3. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-3 How Does E-mail Travel? Messages and attachments sent from first computer – Broken down into pieces – Pieces called packets Routers determine the best way to move messages through Internet System employed to ensure all pieces are received – Packets resent if necessary Messages and attachments reassembled at recipient’s computer

4. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-4 What Is a Communications Protocol? Protocol – Standardized means – Used for coordinating activities – Sequence of ordered steps Communications protocol – Means for coordinating activities between communicating computers Computers agree on protocol to use – Broken down into layers

5. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-5 Layered Protocol Schemes Protocol architectures – Reference Model for Open Systems Interconnection (OSI) Developed by International Organization for Standardization (ISO) – Transmission Control Program/Internet Protocol (TCP/IP) Developed by the Internet Engineering Task Force (IETF) – TCP/IP-OSI architecture is blend

6. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-6 TCP/IP-OSI Architecture Figure CE7-3

7. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-7 Terminology Architecture – Arrangement of protocol layers Each layer performs specific tasks Protocol – Exist at each layer of architecture – Set of rules that accomplish tasks at that layer Program – Specific computer product – Implements a protocol

8. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-8 Layer 5 Protocols – Simple Mail Transfer Protocol (SMTP) Standard e-mail protocol – Hypertext Transfer Protocol (HTTP) Processes Web pages – File Transfer Protocol (FTP) Used to copy files from one computer to another

9. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-9 Layer 4 Transmission Control program (TCP) – Converts from one data representation to another – Breaks e-mail into segments Adds identifying segments to beginning of pieces – Provides reliability Checks to see if all packets are received

10. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-10 Layer 3 Internet Protocol – Interacts with TCP in Layer 4 – Routers send messages across Internet Works through IP Special purpose computers – Packages messages into packets Places IP data in front of TCP data

11. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-11 Layers 1 and 2 Switches facilitate data communications Layer 2 protocols – Program packages packets into frames Basic computer connectivity accomplished at layers 1 and 2

12. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-12 Network Addresses: MAC and IP MAC addresses – Physical addresses – Implemented by programs that use Layer 2 protocols – Each NIC card given an address by manufacturer – Address only shared within network or segment IP addresses – Logical addresses – Written as series of dotted decimals 192.68.2.28 – Not permanently associated with hardware device Can be reassigned as necessary

13. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-13 IP Addresses Two kinds of IP addresses: – Public Used on Internet Assigned by ICANN Each address is unique – Private Used within private networks Controlled by company operating network

14. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-14 Dynamic Host Configuration Protocol DHCP Distributes temporary IP address to computers – Address loaned while computer connected to LAN – When computer disconnected, IP address made available to others

15. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-15 Private IP addresses Assigned manually by network administrator Usually given to: – Web servers – Shared devices Most users are given addresses by DHCP

16. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-16 Networks Figure CE7-1

17. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-17 Using TCP/IP-OSI Protocols Within the Hotel Hotel has private Web server – IP address of server assigned by network administrator Guest computer signs into Web server – Guest browser constructs request for server – Uses HTTP TCP breaks request into segments, adds additional data TCP program hands segments to program that implements IP

18. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-18 Using TCP/IP-OSI Protocols Within the Hotel (continued) IP program adds header into packet Passes on to program that implements Ethernet Ethernet program translates IP address into MAC address Ethernet wraps packet into frame – Sends packet through switch

19. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-19 Switches and Routers Switches – Switch table Table of data – Entries for every device on network – Work with frames in Layer 2 – Use MAC addresses Routers – Routing tables Directs packet traffic on Internet Work with packets in Layer 3 Use IP addresses

20. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-20 Accessing Hotel Web Server Figure CE7-6

21. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-21 Using TCP/IP-OSI Protocols Within the Hotel (continued) Switch consults switch table Directs frame to router Ethernet unpacks frame, send packet to IP Router consults routing table, sends packet one hop down Internet Ethernet determines MAC address needed – Ethernet packages packet into frame addressed to appropriate MAC address – Sends frame to switch

22. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-22 Using TCP/IP-OSI Protocols Within the Hotel (continued) Switch sends frame to destination Ethernet unpacks frame, send packet to IP program IP program strips off header Sends segment to program that implements TCP TCP sends acknowledgement back to guest computer indicating receipt When both segments received, sent to Web server program – Processes HTTP request

23. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-23 Network Address Translation Internet traffic uses public IP addresses – Assigned in blocks Routers may have two IP addresses – Private one assigned by organization for local traffic – Public one assigned by ISP for Internet traffic Network Address Translation – Process of changing public IP addresses into private addresses and reverse – Routers receive packets on Internet and redirects them to individual computers on local network

24. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-24 Your E-mail You enter e-mail address of recipient – E-mail program works at application layer Implements SMTP to send email Uses domain name system to get public IP address E-mail message sent to router – Sends message to TCP Breaks into segments, placed in packets Sent to router Packets sent to Ethernet program – Placed in frame – Sent to switch, sent to router

25. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-25 Your E-mail (continued) Packets arrive at router – Implements NAT – Replaces private IP address with public IP address Router consults table, sends to gateway router of recipient Segments unpacked from packets, sent to TCP program Program waits for all segments, then sends to program that implements SMTP Program operates at Layer 5, puts message in mailbox

26. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-26 E-mail System Figure CE7-7

27. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-27 Domain Name System DNS – Converts user-friendly names into public IP address – Resolves domain name ICANN manages resolution system Domain name – Registered name Uniform Resource Locator (URL) – Document’s Web address

28. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-28 Domain Name Resolution ICANN manages root servers – 13 computers across the world – Maintain lists of IP addresses of servers Domain name resolvers – Cache name and IP address on local file – Used instead of going through entire resolution process

29. © 2008 Prentice Hall, Experiencing MIS, David Kroenke CE 7-29 Active Review How does e-mail travel? What is a communications protocol? What are the functions of the five TCP/IP OSI layers? How does the Internet work? How does www.PrenHall.com become 192.52.0.34.65?www.PrenHall.com