Network Topology

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 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

Bus Topology

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

Ring Topology

Ring Topology (3) Advantages Disadvantages 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

Star Topology

Star Topology (3) Advantages Disadvantages 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

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

Mesh Topology (Web)

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”

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

Hybrid Topology

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

Logical Bus A single node failure does not bring the network down 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

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

Logical Ring (2)

Logical Ring (3) Advantages Disadvantages 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

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