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  1. 1. Data Communications and Internet Technology
  2. 2. Fundamental Networking Concepts <ul><li>A computer network is a collection of computers that communicate with one another over transmission lines. </li></ul><ul><li>Three basic types of networks are: </li></ul><ul><ul><li>Local area networks (LANs)–connects computers that reside in a single geographic location on the premises of the company that operates the LAN. </li></ul></ul><ul><ul><li>Wide area networks (WANs)–connects computers at different geographic sites. </li></ul></ul><ul><ul><li>Internets–a network of networks </li></ul></ul>
  3. 3. Fundamental Networking Concepts (Continued) <ul><li>The networks that comprise an Internet use a large variety of communication methods and conventions, and data must flow seamlessly across them. </li></ul><ul><li>To provide seamless flow, an elaborate scheme called a layered protocol is used. </li></ul>
  4. 4. Figure 5-1 Major Network Types
  5. 5. Figure 5-2 Example Networks
  6. 6. Communications Protocols <ul><li>A protocol is a standard means for coordinating an activity between two or more entities. </li></ul><ul><li>A communications protocol is a means for coordinating activity between two or more communicating computers. </li></ul><ul><li>Two machines must agree on the protocol to use, and they must follow that protocol as they send messages back and forth. </li></ul><ul><li>Communications protocols are broken into levels of layers. </li></ul>
  7. 7. Figure 5-5 TCP/IP-OSI on Your Computer
  8. 8. Layer 4 <ul><li>An email program (which uses SMTP) interacts with another protocol called TCP , or Transmission Control Program (TCP). </li></ul>
  9. 9. Local Area Networks <ul><li>A local area network (LAN) is a group of computers connected together on a single company site. </li></ul><ul><li>Usually the computers are located within a half mile or so of each other, although longer distances are possible. </li></ul><ul><ul><li>The key distinction, however, is that all of the computers are located on property controlled by the company that operates the LAN. </li></ul></ul><ul><li>Computers and printers are connected via a switch , which is a special-purpose computer that receives and transmits messages on the LAN. </li></ul>
  10. 10. Local Area Networks (Continued) <ul><li>Each device on a LAN (computer, printer, etc.) has a hardware component called a network interface card (NIC) that connects the device’s circuitry to the cable. </li></ul><ul><ul><li>The NIC works with programs in each device to implement Layer 1 and Layer 2 protocols. </li></ul></ul><ul><ul><li>Each NIC has a unique identifier, which is called the (MAC) media access control address. </li></ul></ul><ul><li>The computers, printers, switches , and other devices on a LAN are connected using one of two media. </li></ul><ul><ul><li>Most connections are made using unshielded, twisted pair (UTP) cable. </li></ul></ul><ul><ul><li>A device called an RJ-45 connector is used to connect the UTP cable into NIC devices on the LAN. </li></ul></ul>
  11. 11. Figure 5-6 Local Area Network
  12. 12. LANs with Wireless Connections <ul><li>Wireless connections have become popular with LANs. </li></ul><ul><li>The NIC for wireless devices have been replaced by wireless NIC (WNIC). </li></ul><ul><ul><li>For laptop computers, such devices can be cards that slide into the PCMA slot or they can be built-in, onboard devices. </li></ul></ul><ul><li>Several different wireless standard exist </li></ul><ul><ul><li>As of 2005, the most popular is IEEE 802.11g </li></ul></ul><ul><ul><li>The current standard, 802.11g allows speeds of up to 54 Mbps. </li></ul></ul><ul><ul><li>The WNICs operate according to the 802.11 protocol and connect to an access point (AP). </li></ul></ul>
  13. 13. Figure 5-10
  14. 14. Wide Area Networks <ul><li>A wide area network (WAN) connects computers located at physically separated sites. </li></ul><ul><ul><li>A company with offices in Detroit and Atlanta must use a WAN to connect the computers together. </li></ul></ul><ul><ul><li>Because the sites are physically separated, the company cannot string wire from one site to another. </li></ul></ul><ul><li>An Internet service provider (ISP) has three important functions: </li></ul><ul><ul><li>It provides you with a legitimate Internet address. </li></ul></ul><ul><ul><li>It serves as your gateway to the Internet. </li></ul></ul><ul><ul><li>It receives the communication from your computer and passes them on to the Internet, and it receives communication from the Internet and passes them on to you. </li></ul></ul>
  15. 15. DSL Modems <ul><li>A DSL modem is takes the place of a cable connection. </li></ul><ul><li>DSL stands for digital subscriber line. </li></ul><ul><li>DSL modems operate on the same lines as voice telephones and dial-up modems. </li></ul><ul><ul><li>They operate so that their signals do not interfere with voice telephone service. </li></ul></ul><ul><ul><li>They provide much faster data transmission speeds than dial up modems. </li></ul></ul><ul><ul><li>They always maintain a connection. </li></ul></ul>
  16. 16. Virtual Private Network <ul><li>Virtual private network (VPN) is the fourth WAN alternative. </li></ul><ul><li>A VPN uses the Internet or a private internet to create the appearance of private point-to-point connections. </li></ul><ul><li>A VPN uses the public Internet to create the appearance of a private connection. </li></ul><ul><li>A connection called a tunnel , is a virtual pathway over a public or shared network from the VPN client to the VPN server. </li></ul>
  17. 17. Virtual Private Network (Continued) <ul><li>VPN communications are secure. </li></ul><ul><ul><li>The VPN client software encrypts , or codes, the original messages so that its contents are hidden. </li></ul></ul><ul><li>Virtual private networks offer the benefit of point-to-point leased lines, and they enable remote access, both by employees and by any others who have been registered with the VPN server. </li></ul>
  18. 18. Figure 5-18 Remote Access Using VPN: Actual Connections
  19. 19. Domain Name System <ul><li>IP addresses are useful for computer-to-computer communication, but they are not well suited for human use. </li></ul><ul><li>The purpose of the domain name system (DNS) is to convert user-friendly names into their IP addresses. </li></ul><ul><li>Any registered, valid name is called a domain name. </li></ul><ul><li>The process of changing a name into its IP address is called resolving the domain name. </li></ul>