Network Topology

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Network Topology
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Introduction

• Physical and Logical Topologies
• Topologies
• Bus
• Ring
• Star
• Extended Star
• Mesh
• Hybrid

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Physical vs. Logical Topology

• The actual layout of a network and its media is
  its Physical Topology
• The way in which the data access the medium and
  transmits packets is the Logical Topology
• A glance at a network is not always revealing.
  Cables emerging from a Hub does not make it
  necessarily a Star Topology it may actually be
  a bus or a ring

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Bus Topology
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Bus Topology (5)

• Advantages
• Inexpensive to install
• Easy to add stations
• Use less cable than other topologies
• Works well for small networks

• Disadvantages
• No longer recommended
• Backbone breaks, whole network down
• Limited no of devices can be attached
• Difficult to isolate problems
• Sharing same cable slows response rates

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Ring Topology
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Ring Topology (3)

• Advantages
• Data packets travel at great speed
• No collisions
• Easier to fault find
• No terminators required

• Disadvantages
• Requires more cable than a bus
• A break in the ring will bring it down
• Not as common as the bus less devices available

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Star Topology
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Star Topology (3)

• Advantages
• Easy to add devices as the network expands
• One cable failure does not bring down the entire
  network (resilience)
• Hub provides centralised management
• Easy to find device and cable problems
• Can be upgraded to faster speeds
• Lots of support as it is the most used

• Disadvantages
• A star network requires more cable than a ring or
  bus network
• Failure of the central hub can bring down the
  entire network
• Costs are higher (installation and equipment)
  than for most bus networks

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Extended Star Topology
A Star Network which has been expanded to include
an additional hub or hubs.
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Mesh Topology (Web)
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Mesh Topology (2)

• Not common on LANs
• Most often used in WANs to interconnect LANS
• Each node is connected to every other node
• Allows communication to continue in the event of
  a break in any one connection
• It is Fault Tolerant

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Mesh Topology (3)

• Disadvantages
• Expensive
• Difficult to install
• Difficult to manage
• Difficult to troubleshoot

• Advantages
• Improves Fault Tolerance

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Hybrid Topology
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Logical Bus

• Modern Ethernet networks are Star Topologies
  (physically)
• The Hub is at the centre, and defines a Star
  Topology
• The Hub itself uses a Logical Bus Topology
  internally, to transmit data to all segments

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Logical Bus

• Advantages
• A single node failure does not bring the network
  down
• Most widely implemented topology
• Network can be added to or changed without
  affecting other stations

• Disadvantages
• Collisions can occur easily
• Only one device can access the network media at a
  time

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Logical Ring

• Data in a Star Topology can transmit data in a
  Ring
• The MAU (Multistation Access Unit) looks like an
  ordinary Hub, but data is passed internally using
  a logical ring
• It is superior to a Logical Bus Hub see later
  slide

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Logical Ring (2)
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Logical Ring (3)

• Advantages
• The amount of data that can be carried in a
  single message is greater than on a logical bus
• There are no collisions

• Disadvantages
• A broken ring will stop all transmissions
• A device must wait for an empty token to be able
  to transmit

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Summary

• Bus Topology
• Ring Topology
• Star Topology
• Other Topologies
• Logical Topologies
• Questions and Answers