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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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  • Physical and Logical Topologies

  • Topologies

    • Bus

    • Ring

    • Star

    • Extended Star

    • Mesh

    • Hybrid

CP2073 Networking

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

CP2073 Networking

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 !)

CP2073 Networking


  • Cost

  • Scalability

  • Bandwidth Capacity

  • Ease of Installation

  • Ease of fault finding and maintenance

CP2073 Networking

Bus topology
Bus Topology

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

Ring topology
Ring Topology

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

Star topology
Star Topology

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

Extended star topology
Extended Star Topology

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

CP2073 Networking

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”

CP2073 Networking

Mesh topology 3
Mesh Topology (3)


  • Expensive

  • Difficult to install

  • Difficult to manage

  • Difficult to troubleshoot


  • Improves Fault Tolerance

CP2073 Networking

Hybrid topology
Hybrid Topology

CP2073 Networking

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)

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

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

CP2073 Networking

Logical ring 2
Logical Ring (2)

CP2073 Networking

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

CP2073 Networking


  • Bus Topology

  • Ring Topology

  • Star Topology

  • Other Topologies

  • Logical Topologies

  • Questions and Answers

CP2073 Networking