Computer Networks Topologies

A computer network topology is the arrangement and/or structure of the various elements of a computer network that depicts both physically and logically. In this lesson you will learn about the five basic network topologies along with their advantages and disadvantages.   Computer Network Topology
  • Physical Topology: the physical way the network is wired
    • How computers connected to each other
  • Logical Topology: the way messages are sent
    • How to send a message from machine to another
  Basic Network Topologies
  • Point-to-point
    • Connection between two machines through a dedicated media link
    • Cable link or a wireless link
  • Bus
    • Single cable functions as a shared communication media bus (Backbone)
    • Computers attach or tap with an interface connector
    • Terminators at each end of the cable
      • Connected with a Y-piece or T-piece
    • Advantages
      • Simple to design
      • Easy to install
      • Inexpensive due to using
        • Coaxial cable
        • BNC Connectors
    • Disadvantages
      • Less security
        • Allows sniffing
          • Every message passing from one machine to the other can be sniffed by any other machine on the bus
      • Slow during high traffic
        • If high traffic is introduced the speed of the whole network goes down leading to poor performance
      • Lead to collisions
  • Ring
    • Cable connects and node to another to form a ring
    • Messages travel through the ring always in the same direction
    • Data messages are transmitted in frames that circulate all the machines which allows for sniffing
    • Sent frame circulates back to source of the message to acknowledge transmission has been done and to set a frame free for another message
    • Advantages - similar to the Bus Topology
      • Simple to design
      • Easy to install
      • Inexpensive due to using
        • Coaxial cable
        • BNC Connectors
    • Disadvantages
      • The entire network fails if one machine fails
      • Expansion or reconfiguration affects operation
        • You have to break the ring in order to expand or configure
      • Slow for big number of machines
  • Star
    • Each station is connected directly to a central device
    • The connection is like a number of point-to-point links
    • Central devices is Hub or Switch
    • Switch is more recent technology and more secure device than hub
      • Switch does not allow sniffing
      • Hub allows sniffing
    • Advantages
      • Network not affected if one machine fails
      • Network expansion and reconfiguration is simple
      • Troubleshooting is easy
    • Disadvantages
      • If the central device fails all the network fails
  • Mesh
    • Connect all devices with multiple paths
      • Every device is connected to the other devices through a separate link
    • Offers a very high redundancy
      • Very high reliability
    • N=n*(n-1)/2
      • N= number of cables
      • n= number of connected nodes
      • This equation is used to calculate the number of cables used in any Mesh Topology to know the number of connected nodes
    • Advantages
      • Faults tolerant
        • Allows broken cables to exist without breaking the whole topology
      • Secure (High availability)
    • Disadvantages
      • Expensive due to redundancy
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