1 CP2073 Networking Lecture 5. CP2073 Networking 2 Introduction 8Physical and Logical Topologies...
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Transcript of 1 CP2073 Networking Lecture 5. CP2073 Networking 2 Introduction 8Physical and Logical Topologies...
1
CP2073 Networking
Lecture 5
CP2073 Networking 2
Introduction Physical and Logical Topologies Topologies
Bus Ring Star Extended Star Mesh Hybrid
CP2073 Networking 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
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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 !)
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Factors
Cost Scalability Bandwidth Capacity Ease of Installation Ease of fault finding and
maintenance
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Bus Topology
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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
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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
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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
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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 (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
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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 (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
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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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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)
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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
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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