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Chapter 8


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Chapter 8

  1. 1. Chapter 8 Computer Network 8.1 The needs for Networking 144 8.2 LAN vs WAN 147 8.3 Hardware for a Network 149 8.4 Common Services on a Network 152
  2. 2. 8.1 The needs for Networking (1) <ul><li>Standalone Computers </li></ul><ul><ul><li>Early computers </li></ul></ul><ul><ul><li>Using floppy disk to transfer files </li></ul></ul><ul><ul><li>Reconnection is needed in sharing a printer </li></ul></ul>Chapter 8 Computer Network
  3. 3. 8.1 The needs for Networking (2) <ul><li>Advantages of a Network: </li></ul><ul><ul><li>1. Communication </li></ul></ul><ul><ul><ul><li>Users may communicate with each other through e-mails, notice boards, chat rooms, newsgroups, videoconferencing etc. </li></ul></ul></ul><ul><ul><ul><li>Each user is identified by a user name </li></ul></ul></ul><ul><ul><ul><li>Requiring both the user name and password to log on the system </li></ul></ul></ul><ul><ul><li>2. Sharing of hardware </li></ul></ul><ul><ul><ul><li>Some hardware can be shared out </li></ul></ul></ul><ul><ul><ul><li>e.g. Laser printer </li></ul></ul></ul><ul><ul><li>3. Sharing of data </li></ul></ul><ul><ul><ul><li>Folders and files in a computer can be shared out to allow authorised users to access. </li></ul></ul></ul>Chapter 8 Computer Network
  4. 4. 8.1 The needs for Networking (3) <ul><li>File server </li></ul><ul><ul><li>a computer where files are centralised </li></ul></ul><ul><ul><li>Fault tolerent, faster and larger storage capacity </li></ul></ul><ul><ul><li>Advantages: </li></ul></ul><ul><ul><ul><li>1. Data is always up-to-date. Can be updated by different users. </li></ul></ul></ul><ul><ul><ul><li>2. Data treated with more intensive care </li></ul></ul></ul><ul><ul><ul><ul><li>More frequent back up </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Automatic file duplication using another hard disk. </li></ul></ul></ul></ul><ul><ul><ul><li>3. Better file management - easy to tell which one is the most updated </li></ul></ul></ul>Chapter 8 Computer Network
  5. 5. 8.1 The needs for Networking (4) <ul><li>Advantages of a Network: </li></ul><ul><ul><li>4. Sharing of Internet Access </li></ul></ul><ul><ul><ul><li>A network, connected to the Internet, allows all users to access the Internet </li></ul></ul></ul><ul><ul><ul><li>using a single Internet account provided by ISP </li></ul></ul></ul><ul><ul><li>5. Sharing of Software </li></ul></ul><ul><ul><ul><li>Network version </li></ul></ul></ul><ul><ul><ul><ul><li>accessed from computers within the network </li></ul></ul></ul></ul><ul><ul><ul><ul><li>avoids installing the software in all computers </li></ul></ul></ul></ul><ul><ul><ul><ul><li>less expensive than individual copies for all the computers </li></ul></ul></ul></ul>Chapter 8 Computer Network
  6. 6. 8.2 LAN vs WAN <ul><li>1. LAN </li></ul><ul><li>2. WAN </li></ul>Chapter 8 Computer Network
  7. 7. 8.2.1 LAN (1) <ul><li>Local Area Network (LAN) </li></ul><ul><ul><li>linking computers/devices over short distances </li></ul></ul><ul><ul><li>Connection by </li></ul></ul><ul><ul><ul><li>cables </li></ul></ul></ul><ul><ul><ul><li>wireless media </li></ul></ul></ul><ul><ul><ul><ul><li>e.g. radio waves </li></ul></ul></ul></ul><ul><ul><li>Examples: </li></ul></ul><ul><ul><ul><li>home </li></ul></ul></ul><ul><ul><ul><li>school campuses </li></ul></ul></ul><ul><ul><ul><li>office buildings </li></ul></ul></ul>8.2 LAN vs WAN
  8. 8. 8.2.1 LAN (2) <ul><ul><li>1. LANs used at Home </li></ul></ul><ul><ul><ul><li>For sharing Internet access </li></ul></ul></ul><ul><ul><ul><li>Computers are usually joined peer-to-peer </li></ul></ul></ul><ul><ul><ul><li>Easy to set up, but weak in security </li></ul></ul></ul><ul><ul><ul><li>All the computers are workstations/No server for maintaining the network user accounts </li></ul></ul></ul><ul><ul><li>2. LANs used in Schools and Working Places </li></ul></ul><ul><ul><ul><li>Client/server based </li></ul></ul></ul><ul><ul><ul><li>Server </li></ul></ul></ul><ul><ul><ul><ul><li>maintains the network user accounts </li></ul></ul></ul></ul><ul><ul><ul><ul><li>responds to requests from the client computers (i.e. workstations) on the network. </li></ul></ul></ul></ul>8.2 LAN vs WAN
  9. 9. 8.2.1 LAN (3) <ul><ul><li>School LAN </li></ul></ul><ul><ul><ul><li>teaching materials are stored in the file server </li></ul></ul></ul><ul><ul><ul><li>Examination papers stored in area which is inaccessible to students </li></ul></ul></ul><ul><ul><ul><li>Should be linked to the Internet </li></ul></ul></ul><ul><ul><ul><ul><li>where a huge store of information for teaching and learning is available </li></ul></ul></ul></ul><ul><ul><li>Working place </li></ul></ul><ul><ul><ul><li>Several staff may update the same file at different times </li></ul></ul></ul><ul><ul><ul><ul><li>only authorised users can access </li></ul></ul></ul></ul><ul><ul><ul><li>Communication </li></ul></ul></ul><ul><ul><ul><ul><li>Staff may communicate by sending e-mails, messages or participating in videoconferencing using the LAN </li></ul></ul></ul></ul>8.2 LAN vs WAN
  10. 10. 8.2.2 WAN (1) <ul><li>Wide Area Network (WAN) </li></ul><ul><ul><li>covers a large geographic area using </li></ul></ul><ul><ul><ul><li>dedicated telephone lines or </li></ul></ul></ul><ul><ul><ul><li>radio waves </li></ul></ul></ul><ul><ul><li>Consisting of two or more LANs </li></ul></ul><ul><ul><li>Used in international banks </li></ul></ul><ul><ul><li>The Internet is the world's largest WAN </li></ul></ul>8.2 LAN vs WAN
  11. 11. 8.2.2 WAN (2) <ul><ul><li>Router </li></ul></ul><ul><ul><ul><li>Connect two networks </li></ul></ul></ul><ul><ul><ul><li>Direct the traffic of data flow </li></ul></ul></ul><ul><ul><ul><ul><li>modems are needed if connection via telephone line </li></ul></ul></ul></ul><ul><ul><li>WAN used in a Bank </li></ul></ul><ul><ul><ul><li>Each branch consists of a LAN </li></ul></ul></ul><ul><ul><ul><li>Transactions done in a branch must be updated immediately to the computer at the headquarter </li></ul></ul></ul><ul><ul><ul><li>The LAN of each branch is connected via dedicated telephone lines (or optical fibres) to the LAN at the headquarter. </li></ul></ul></ul><ul><ul><ul><li>This forms a WAN </li></ul></ul></ul>8.2 LAN vs WAN
  12. 12. 8.3 Hardware for a Network <ul><li>1. Basic Hardware for a LAN </li></ul><ul><li>2. Wireless LAN </li></ul><ul><li>3. Remote Access to a LAN </li></ul><ul><li>4. Transmission Rate </li></ul>Chapter 8 Computer Network
  13. 13. 8.3.1 Basic Hardware for a LAN <ul><li>1. Network interface card (NIC) </li></ul><ul><ul><ul><li>Installed in all computers, both client and server </li></ul></ul></ul><ul><ul><ul><li>controls the exchange of data among computers </li></ul></ul></ul><ul><li>2. Transmission medium </li></ul><ul><ul><li>A. Copper wire </li></ul></ul><ul><ul><ul><li>Connecting computers on the same floor </li></ul></ul></ul><ul><ul><li>B. Optical fibre </li></ul></ul><ul><ul><ul><li>Connecting between floors in a building </li></ul></ul></ul><ul><ul><li>C. Radio waves </li></ul></ul><ul><li>3. Switch/hub </li></ul><ul><ul><ul><li>Connects all the cables together physically </li></ul></ul></ul><ul><ul><ul><li>Switch is faster than a hub </li></ul></ul></ul>8.3 Hardware for a Network
  14. 14. 8.3.2 Wireless LANs (1) <ul><li>1. Access point </li></ul><ul><ul><li>Behaves like a switch or hub </li></ul></ul><ul><ul><li>Connecting all computers via radio waves </li></ul></ul><ul><li>2. Wireless NICs </li></ul><ul><ul><li>Installed in the computers </li></ul></ul><ul><ul><li>Communicate with the access point via radio waves </li></ul></ul>8.3 Hardware for a Network
  15. 15. 8.3.2 Wireless LANs (2) <ul><li>Advantages: </li></ul><ul><ul><li>Saves the cost in laying cables </li></ul></ul><ul><ul><li>Eliminates the cluttering of wires </li></ul></ul><ul><ul><li>More flexible </li></ul></ul><ul><ul><ul><li>Workstations can be added easily </li></ul></ul></ul><ul><ul><ul><ul><li>as long as the access point can handle </li></ul></ul></ul></ul><ul><ul><ul><li>Workstations can be located anywhere </li></ul></ul></ul><ul><ul><ul><ul><li>so far as the radio waves can be received </li></ul></ul></ul></ul>8.3 Hardware for a Network
  16. 16. 8.3.3 Remote access to a LAN <ul><li>Modem </li></ul><ul><ul><li>short for modulator-demodulator </li></ul></ul><ul><ul><li>Signals for </li></ul></ul><ul><ul><ul><li>Computer: Digital </li></ul></ul></ul><ul><ul><ul><li>Telephone line: Analog </li></ul></ul></ul><ul><ul><li>A modem: Digital <--> Analog </li></ul></ul><ul><li>Dial-up Access </li></ul><ul><ul><li>Using ordinary telephone lines and regular modem </li></ul></ul><ul><ul><li>e.g. remote access from a home to an office </li></ul></ul><ul><ul><li>Disadvantages: </li></ul></ul><ul><ul><ul><li>Connection is temporary </li></ul></ul></ul><ul><ul><ul><li>Data transfer rate is slow </li></ul></ul></ul>8.3 Hardware for a Network
  17. 17. 8.3.4 Speed of Data Transfer <ul><li>Bandwidth </li></ul><ul><ul><li>Speed of data transmission on a network </li></ul></ul><ul><ul><li>Measured in Mbps (megabits per second) </li></ul></ul><ul><ul><li>Actual data transfer rate is much less than the bandwidth </li></ul></ul><ul><ul><ul><li>because of the overhead in transmission </li></ul></ul></ul>8.3 Hardware for a Network
  18. 18. 8.4 Common Services on a Network <ul><ul><li>1. File server </li></ul></ul><ul><ul><li>2. Print server </li></ul></ul><ul><ul><li>3. Mail server </li></ul></ul><ul><ul><li>4. Web server </li></ul></ul><ul><ul><ul><li>stores the contents of web pages </li></ul></ul></ul><ul><ul><ul><li>entertains requests from other users on the Internet </li></ul></ul></ul><ul><ul><li>5. Proxy server </li></ul></ul><ul><ul><ul><li>improves the efficiency of Internet access </li></ul></ul></ul><ul><ul><ul><li>filters web pages </li></ul></ul></ul><ul><ul><ul><ul><li>to prevent users from accessing certain sites. </li></ul></ul></ul></ul>Chapter 8 Computer Network