Transcript NETWORK TOPOLOGIES

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
CP2073 Networking
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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 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
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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
Disadvantages
The amount of data A broken ring will
that can be carried
stop all
in a single message
transmissions
is greater than on a A device must wait
logical bus
for an empty token
There are no
to be able to
collisions
transmit
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Summary
Bus Topology
Ring Topology
Star Topology
Other Topologies
Logical Topologies
Questions and Answers
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Bibliography
Source: Web Quests
CP2073 Networking
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