Network Topology

1. Network Topology

2. Introduction • Physical and Logical Topologies • Topologies • Bus • Ring • Star • Extended Star • Mesh • Hybrid

3. 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

4. Bus Topology

5. Bus Topology (5) 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 Advantages • Inexpensive to install • Easy to add stations • Use less cable than other topologies • Works well for small networks

6. Ring Topology

7. 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

8. Star Topology

9. 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

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

11. Mesh Topology (Web)

12. 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”

13. Mesh Topology (3) Disadvantages • Expensive • Difficult to install • Difficult to manage • Difficult to troubleshoot Advantages • Improves Fault Tolerance CP2073 Networking

14. Hybrid Topology

15. 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

16. 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

17. 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

18. Logical Ring (2)

19. 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

20. Summary • Bus Topology • Ring Topology • Star Topology • Other Topologies • Logical Topologies • Questions and Answers