Cp2073 networking
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CP2073 Networking. Lecture 5. Introduction. Physical and Logical Topologies Topologies Bus Ring Star Extended Star Mesh Hybrid. Physical vs. Logical Topology. The actual layout of a network and its media is its Physical Topology

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CP2073 Networking

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Cp2073 networking

CP2073 Networking

Lecture 5



  • Physical and Logical Topologies

  • Topologies

    • Bus

    • Ring

    • Star

    • Extended Star

    • Mesh

    • Hybrid

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Physical vs logical topology

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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Physical vs logical topology 2

Physical vs. Logical Topology (2)

  • Your choice of Logical Topology will affect the Physical Topology – and vice versa

  • Design carefully – it may be difficult to change part way through the installation

  • Your choice will determine cable installation, network devices, network connections, protocols (and where you will drill holes in the building !)

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  • Cost

  • Scalability

  • Bandwidth Capacity

  • Ease of Installation

  • Ease of fault finding and maintenance

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Bus topology

Bus Topology

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Bus topology 2

Bus Topology (2)

  • Network maintained by a single cable

  • Cable segment must end with a terminator

  • Uses thin coaxial cable (backbones will be thick coaxial cable)

  • Extra stations can be added in a daisy chain manner

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Bus topology 3

Bus Topology (3)

  • Standard is IEEE 802.3

  • Thin Ethernet (10Base2) has a maximum segment length of 200m

  • Max no. of connections is 30 devices

  • Four repeaters may be used to a total cable length of 1000m

  • Max no. of nodes is 150

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Bus topology 4

Bus Topology (4)

  • Thick Ethernet (10Base5) used for backbones

  • Limited to 500m

  • Max of 100 nodes per segment

  • Total of four repeaters , 2500m, with a total of 488 nodes

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Bus topology 5

Bus Topology (5)


  • 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


  • Inexpensive to install

  • Easy to add stations

  • Use less cable than other topologies

  • Works well for small networks

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Ring topology

Ring Topology

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Ring topology 2

Ring Topology (2)

  • No beginning or end (a ring in fact !!)

  • All devices of equality of access to media

  • Single ring – data travels in one direction only, guess what a double ring allows !?

  • Each device has to wait its turn to transmit

  • Most common type is Token Ring (IEEE 802.5)

  • A token contains the data, reaches the destination, data extracted, acknowledgement of receipt sent back to transmitting device, removed, empty token passed on for another device to use

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Ring topology 3

Ring Topology (3)


  • Data packets travel at great speed

  • No collisions

  • Easier to fault find

  • No terminators required


  • 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

Star Topology

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Star topology 2

Star Topology (2)

  • Like the spokes of a wheel (without the symmetry)

  • Centre point is a Hub

  • Segments meet at the Hub

  • Each device needs its own cable to the Hub

  • Predominant type of topology

  • Easy to maintain and expand

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Star topology 3

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

Extended Star Topology

A Star Network which has been expanded to include an additional hub or hubs.

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Mesh topology web

Mesh Topology (Web)

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Mesh topology 2

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

Mesh Topology (3)


  • Expensive

  • Difficult to install

  • Difficult to manage

  • Difficult to troubleshoot


  • Improves Fault Tolerance

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Hybrid topology

Hybrid Topology

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Hybrid topology 2

Hybrid Topology (2)

  • Old networks are updated and replaced, leaving older segments (legacy)

  • Hybrid Topology – combines two or more different physical topologies

  • Commonly Star-Bus or Star-Ring

  • Star-Ring uses a MAU (Multistation Access Unit (see later slide)

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Types of logical topology

Types of Logical Topology

  • Previous slides showed Physical Topologies

  • Only two Logical Topologies (Bus or Ring)

  • Physical Bus or Ring easy to conceptualise

  • Physical Star could be either a Bus or Ring in logical terms

  • Confused ? See next slides

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Logical bus

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 bus1

Logical Bus


  • 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


  • Collisions can occur easily

  • Only one device can access the network media at a time

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Logical ring

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

Logical Ring (2)

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Logical ring 3

Logical Ring (3)


  • The amount of data that can be carried in a single message is greater than on a logical bus

  • There are no collisions


  • A broken ring will stop all transmissions

  • A device must wait for an empty token to be able to transmit

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  • Bus Topology

  • Ring Topology

  • Star Topology

  • Other Topologies

  • Logical Topologies

  • Questions and Answers

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