S4 CIT

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S4 CIT

• Computer Network

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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?

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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.

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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.

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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 worlds largest WAN.

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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.

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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 (??) to different users, so security is
  high.
• Examples School network, Playing on-line games

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Hardware Requirementfor a Network - NIC

• NIC (Network Interface Card)
• also called LAN Card
• an expansion board added to the computers
  motherboard
• key hardware component for connecting the
  computer to a network (wired or wireless)

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Hardware Requirementfor a Network - NIC

• NIC can be connected to the computer by means of
• PCI Bus
• USB Bus
• PCMCIA Bus (In Notebook Computer)

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Hardware Requirementfor a Network
Transmission Medium

• Data and signal need to be transmitted over a
  network through a medium (??)
• It can be a cable (wired) or through microwave
  (wireless)

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Transmission Medium Twisted-pair Cable

• Sometimes called the UTP Cable (Unshielded
  Twisted Pair).
• 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.

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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.

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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.

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Transmission Medium Microwave

• Electromagnetic waves which can wirelessly carry
  data through the atmosphere
• It travels in straight line from one microwave
  relay station(???) to another.

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Hardware Requirementfor a Network Connecting
Devices

• Hub
• provides a central connection point for cables in
  a network
• slower than switch

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Hardware Requirementfor a Network Connecting
Devices

• Switch
• advanced type of hubs
• faster than hubs

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Hardware Requirementfor a Network Connecting
Devices

• Router
• connect multiple networks
• connect LANs to form a WAN
• connect a LAN to the Internet

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Wireless Network

• Usually a Wireless LAN (WLAN)
• Use microwave (Radio Frequency, 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.

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Wireless Network
Wireless PCMCIA Card
Wireless NIC
Access Point
Wireless USB Adapter
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Advantages of usingWireless 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.

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MODEM

• MODEM Modulator and Demodulator
• Modulate
• Convert a digital signal into analogue signal.
• Demodulate
• Convert an analogue signal into digital signal.

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MODEM

• Analogue Signal (????)
• Can be transmitted along telephone lines and UTP
• Digital Signal (????)
• ie 01011010
• Computer can only process digital signal

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Using MODEMto connect to the Internet

• Traditionally,
• Use telephone lines
• Speed 56kbps
• Nowadays
• Use telephone lines UTP Cables
• Called ADSL MODEM
• Speed 1.5Mbps, 3Mbps, 6Mbps

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Network Topology

• It is the logical layout or the way in which the
  computers and other devices are connected.
• Types
• Ring
• Star
• Bus

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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.

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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.

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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.

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Comparison ofdifferent 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.

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Comparison ofdifferent Topologies - Star

• Star Topology
• Advantage
• One device failed will not
• affect the other devices
• Disadvantage
• If the server breaks down, the whole network
  fails.

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Comparison ofdifferent 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.

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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.

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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.

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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.

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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 servers 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

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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

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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
  schools Windows 2000 Server.

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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.

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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 differences of Yahoo! Mail and Outlook
  Express

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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.

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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

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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.

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