4.3.1 - Networks - Network Topologies

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  • Created by: Annie
  • Created on: 07-05-13 19:16
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  • Network Topologies
    • Star
      • What is it?
        • The switch manages and controls all functions of the network
          • It also acts as a repeater for the data flow to maintain signal strength
        • Data passes through the switch/hub before continuing to its destination
        • A star topology is designed with each node (tile server, workstations and peripherals) connected directly to a central network, switch or hub
      • Advantages
        • If one cable fails, the other stations are not affected
        • Consistent performance even under heavy use
        • Reliable market proven system
        • Few problems with data collision since each station has its own cable to the server
        • Security can be implemented in the hub/swith
      • Disadvantages
        • May be costly to install because of the cable lengths required
        • The speed of the network is dependent on the quality of the switch/hub
        • If the central hub/switch fails, the whole network goes down
    • Ring
      • What is it?
        • Connects computers on a single circle of cable
          • No terminated ends
        • Signals travel around the loop in one direction and pass through each computer, which can act as a repeater to boost the signal and send it on to the next computer
        • It is a Peer to Peer network
        • One method of transmitting data around a ring is called Token Passing
          • The Token is passed from computer to computer until it gets to a computer that has data to send
            • The data is read by each computer until it reaches the computer with the destination address
              • The receiving computer returns a message to the sending computer indicating that the data has been received
                • After verification, the sending computer creates a new token and releases it on the network
      • Advantages
        • High data transmission rates are possible
        • Transmission around the network is one way only
        • Each computer has the same level of access, so no one PC can dominate communications
        • No dependence on a central computer or file server... each node controls communication to and from itself
      • Disadvantages
        • If one node breaks down or a cable is broken, the data transmission fails
        • To add new devices to the network, all activity must cease until the work is finished
        • Faults in the cable are difficult to locate
        • If used over large distances, a repeater is required because of degradation of signal
          • Over a large distance, the amount of cable required is greater
    • Bus/Ethernet
      • What is it?
        • All the devices on the network (server, PCs, printers etc) are connected by a common main cable
        • Data flows in both directions on the cable
        • Terminators are used at either end to "absorb" unused communications
      • Advantages
        • Inexpensive to install as it requires the least amount of cable
        • Easy to add more stations without disrupting the network but there is a limit to the number of stations
        • Easy to install as it requires just a single main run of cable
      • Disadvantages
        • Information can be transmitted in either direction and occasionally there is data collision
        • Network performance degrades under a heavy load
          • 12+ is considered a heavy load
        • Can't remove the cables or change calbles
          • Any changes will disrupt the network
        • Cable failure is difficult to isolate without the correct equipment
        • If the main cable breaks, the whole system goes down
    • "The way in which the network is constructed"

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