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S4 CIT Computer Network In the past...



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  • 1. S4 CIT
    • Computer Network
  • 2. In the past…
    • Computers are standalone machine.
    • What can we do if we want to…
      • share a file with someone?
      • print a file but the printer is connected to another computer?
  • 3.  
  • 4. Computer Network
    • It is a system in which two or more computers are connected so that
      • data communications
      • resources sharing ( File sharing , hardware sharing e.g. printer)
    • among the computers become possible.
  • 5. Types of Network
    • LAN (Local Area Network)
      • links computer and other peripheral devices over short distances .
      • For examples:
        • network at home
        • network in school campuses and offices
      • a LAN with an internal e-mail system, file server or message board is called Intranet .
  • 6. Types of Network
    • WAN (Wide Area Network)
      • covers a large geographic area using a communication channel such as dedicated telephone lines and radio waves .
      • a WAN consists of two or more LANs .
      • The Internet is the world’s largest WAN .
  • 7. Network Connection Protocol
    • Peer to Peer
      • Every computer is connected directly to every other computer.
      • Each computer can use information from, and provide information to each other.
      • There is no server.
      • Security is weak .
      • Example is WinMX.
  • 8. Network Connection Protocol
    • Client / Server
      • Individual computers (clients or workstations) are connected to a central computer ( server ).
      • Server computer maintains the network user accounts.
      • Clients can access programs or files stored on the server.
      • Clients request for services whereas servers provide services .
      • Since the server can give different levels of rights ( 權力 ) to different users, so security is high .
      • Examples: School network, Playing on-line games
  • 9. Hardware Requirement for a Network - NIC
    • NIC ( N etwork I nterface C ard)
      • also called LAN Card
      • an expansion board added to the computer’s motherboard
      • key hardware component for connecting the computer to a network (wired or wireless)
  • 10. Hardware Requirement for a Network - NIC
    • NIC can be connected to the computer by means of:
      • PCI Bus
      • USB Bus
      • PCMCIA Bus (In Notebook Computer)
  • 11. Hardware Requirement for a Network – Transmission Medium
    • Data and signal need to be transmitted over a network through a medium ( 媒體 )
    • It can be a cable (wired) or through microwave (wireless)
  • 12. Transmission Medium – Twisted-pair Cable
    • Sometimes called the UTP Cable ( U nshielded T wisted P air).
    • Looks similar to telephone cable
    • The most commonly used types of twisted pair wire is Cat5 cable .
    • The connector of this kind of cable is called RJ45 .
  • 13. Transmission Medium – Coaxial Cable
    • Transmit at a higher speed when compared with twisted-pair cables
    • Can transmit signal over long distances so they can be laid underground or underwater.
  • 14. Transmission Medium – Optical Fibre
    • Bundles of smooth, hair-thin strands of glass
    • Transmit data with high efficiency in terms of light beams
    • Can transmit signal over long distances
    • Largely replaced coaxial cables nowadays.
  • 15.  
  • 16. Transmission Medium – Microwave
    • Electromagnetic waves which can wirelessly carry data through the atmosphere
    • It travels in straight line from one microwave relay station ( 轉發站 ) to another.
  • 17. Hardware Requirement for a Network – Connecting Devices
    • Hub
      • provides a central connection point for cables in a network
      • slower than switch
  • 18. Hardware Requirement for a Network – Connecting Devices
    • Switch
      • advanced type of hubs
      • faster than hubs
  • 19. Hardware Requirement for a Network – Connecting Devices
    • Router
      • connect multiple networks
      • connect LANs to form a WAN
      • connect a LAN to the Internet
  • 20. Wireless Network
    • Usually a Wireless LAN (WLAN)
    • Use microwave ( R adio F requency, RF) to transmit and receive data over air
    • Have same features as a LAN, but without the limitations of a cable.
    • Access Point (AP)is required in a WLAN.
    • It is a device that transports data between a wireless LAN and a wired LAN .
    • wireless NICs are also required in each workstation .
  • 21. Wireless Network Wireless NIC Access Point Wireless PCMCIA Card Wireless USB Adapter
  • 22. Advantages of using Wireless network
    • Save the cost in laying network cables
    • No cluttering of cables
    • More flexible when adding workstations
    • Notebook computer can access network at anywhere under the coverage area.
  • 23. MODEM
    • MODEM – Mo dulator and Dem odulator
    • Modulate
      • Convert a digital signal into analogue signal.
    • Demodulate
      • Convert an analogue signal into digital signal.
  • 24. MODEM
    • Analogue Signal ( 模擬信息 )
      • Can be transmitted along telephone lines and UTP
    • Digital Signal ( 數 碼 信息 )
      • ie: 01011010
      • Computer can only process digital signal
  • 25.  
  • 26. Using MODEM to connect to the Internet
    • Traditionally,
      • Use telephone lines
      • Speed 56kbps
    • Nowadays
      • Use telephone lines & UTP Cables
      • Called ADSL MODEM
      • Speed 1.5Mbps, 3Mbps, 6Mbps
  • 27. Network Topology
    • It is the logical layout or the way in which the computers and other devices are connected.
    • Types:
      • Ring
      • Star
      • Bus
  • 28. Ring Topology
    • All devices are connected on a circular path
    • data flows in one direction .
    • When a computer sends data, the data travels to each computer on the ring until it reaches its destination .
  • 29. Star Topology
    • All devices on the network connect to a central computer (usually a server)
    • All data transferred from one computer to another passes through the server.
  • 30. Bus Topology
    • All computers and other devices are connected to a single central cable .
    • It is flexible because
      • computer can be attached to or detached from the network without disturbing the rest of the network .
  • 31. Comparison of different Topologies - Ring
    • Ring Topology
      • Advantage:
        • Easy and cheap to setup
      • Disadvantage:
        • Data transmission in one direction.
        • Failure of a single device means all devices after cannot function.
  • 32. Comparison of different Topologies - Star
    • Star Topology
      • Advantage:
        • One device failed will not
        • affect the other devices
      • Disadvantage:
        • If the server breaks down, the whole network fails.
  • 33. Comparison of different Topologies - Bus
    • Bus Topology
      • Advantage:
        • Failure of one device
        • will not affect other
        • devices.
      • Disadvantage:
        • Failure of the cable means the whole network is broken down.
  • 34. Practical Network Topology
    • more than one topology is used in a network .
    • For example,
      • in a school network,
      • a bus-star topology is used with a high bandwidth bus as the backbone (usually a optical fibre).
      • the backbone connects a number of star networks such as a LAN inside the computer room.
  • 35. Network Operating System
    • Windows 98/ME, Windows 2000/XP, Linux, etc include the software necessary to establish communication with a network server.
    • Old operating system like DOS do not have these network features.
  • 36. Brief Introduction to OS
    • The most important program that runs on a computer.
    • Every general-purpose computer must have an OS to run other programs.
    • OS perform basic tasks
      • recognizing input from the keyboard
      • sending output to the display screen
      • keeping track of files and directories on the disk
      • controlling peripheral devices such as disk drives and printers.
  • 37. Network Server Software
    • multi-user
    • like a traffic cop
      • different programs and users running at the same time do not interfere with each other.
      • controls file access from the server’s hard disk
      • manages the print queue
    • responsible for security
      • ensuring that unauthorized users do not access the system.
      • tracks user data such as user IDs and passwords
    • Examples include Windows 2000 Server Edition, Windows 2003 Server Edition
  • 38. Network Client Software
    • Gathers login information
    • Handles drive mapping
    • Directs printouts to the network printer
    • Examples include Windows 98/ME, Windows 2000/XP Home or Professional Edition
  • 39. Practical Consideration
    • The server and the client software components do not necessarily have to match.
    • A Windows NT computer in library and some Windows XP computer in classroom can login to the school’s Windows 2000 Server.
  • 40. Common Services on Network - File server
    • A high speed computer that stores the programs and data files shared by users.
    • Most file servers also store user accounts and the network information .
    • Data in a file server are important and must be back up regularly.
  • 41. Common Services on Network - Mail server
    • It provides e-mail services to users.
    • Each user has a mailbox which stores the incoming mails and copies of sent mails .
    • Note the difference s of Yahoo! Mail and Outlook Express
  • 42. Common Services on Network - Print server
    • It manages one or more printers on a network.
    • It allows a shared printer to be accessed by authorized users .
    • Sometimes, a Print Server may not be a computer.
    • In most case, it is connected to the main server in the LAN.
    • But a workstation can also act as a Print Server.
  • 43. Common Services on Network - Web server
    • A web server stores the contents of web pages .
    • It delivers web pages according to the requests from other users on the Internet.
    • Web pages are delivered through a program called web server program. Eg: Microsoft IIS, Apache
  • 44. Common Services on Network - Proxy server
    • It improves the efficiency of Internet access by temporarily storing copies of web pages visited by previous users of the same LAN.
    • It also filters web pages to prevent users from accessing certain sites.
  • 45.