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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)Advantages Improves Fault

Tolerance

Disadvantages Expensive Difficult to install Difficult to

manage Difficult to

troubleshoot

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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 BusAdvantages 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

Bibliography

Source: Web Quests

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