Network Topologies
LAN topologies
WAN topologies
Objectives
Understand the different types of
Networks available.
Understand Networks topologies
Understand categories of Networks
topologies
Understand issues related to
various topologies
What is a topology?

The topology of a network defines how
the nodes of a network are connected.
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Why topologies are important
Design Efficient Protocols
 Create Accurate Model for Simulation
 Derive Estimates for Topological
Parameters
 Study Fault Tolerance and Anti-Attack
Properties
 Solve Internetworking Problems:

◦ - routing
◦ - resource reservation
◦ - administration
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LAN topologies

There are two basic categories of
network topologies:
◦ a physical topology.
◦ a logical topology.
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LAN topologies

Physical
Describes the geometric arrangement of
components that make up the LAN
defines how the nodes of a network are
connected.

Logical
Describes the possible connections between
pairs of networked end-points that can
communicate
Define how data is transmitted between nodes
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What determines a topology?

Physical topology
capabilities of the network access devices and
media, the level of control or fault tolerance
desired, and the cost associated with cabling or
telecommunications circuits.
logical topology, in contrast, is the way that
the signals act on the network media, or the
way that the data passes through the network
from one device to the next without regard to
the physical interconnection of the devices. A
network's logical topology is not necessarily
the same as its physical topology.
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LAN Topologies(Physical)
1)
2)
3)
4)
5)
Bus
Star
Ring
Mesh
Hierarchies/Hybrid
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Bus topology
All networked nodes are interconnected,
peer to peer, using a single, open-ended
cable
 Both ends of the bus must be terminated
with a terminating resistor to prevent
signal bounce

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Bus topology
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Advantages of Bus topology
1)
2)
3)
4)
Easy to implement and extend
Well suited for temporary networks
that must be set up in a hurry
Typically the least cheapest topology to
implement
Failure of one station does not affect
others
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Disadvantages of Bus topology
1)
2)
3)
4)
5)
Difficult to administer/troubleshoot
Limited cable length and number of
stations
A cable break can disable the entire
network; no redundancy
Maintenance costs may be higher in the
long run
Performance degrades as additional
computers are added
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Ring topology
started out as a simple peer-to-peer LAN
topology
 Each networked workstation had two
connections: one to each of its nearest
neighbors
 Data was transmitted unidirectionally
around the ring
 Sending and receiving of data takes place
by the help of TOKEN

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Token Passing
Token contains a piece of information
which along with data is sent by the
source computer
 This token then passes to next node,
which checks if the signal is intended to it

If yes, it receives it and passes the empty to
into the network
otherwise passes token along with the data
to next node
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Ring topology
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Advantages of Ring topology
1)
2)
3)
4)
5)
This type of network topology is very
organized
Performance is better than that of Bus
topology
No need for network server to control the
connectivity between workstations
Additional components do not affect the
performance of network
Each computer has equal access to
resources
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Disadvantages of Ring topology
1)
2)
3)
Each packet of data must pass through
all the computers between source and
destination, slower than star topology
If one workstation or port goes down,
the entire network gets affected
Network is highly dependent on the
wire which connects different
components
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Ring topology
Can be developed fairly easily from a peerto-peer network by adding one transmission
facility and an extra port on two routers
 A ring-shaped WAN constructed with
point-to-point transmission facilities can be
used to interconnect a small number of
sites and provide route redundancy at a
potentially minimal incremental cost
 Can use dynamic routing protocols

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Ring topology
User Location A
T1
T1
User Location B
T1
T1
User Location C
User Location D
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Advantages/Disadvantages of Ring
topology

Advantages:
It provides alternative routes
It is less expensive than all but the peer-topeer WAN

Disadvantages:
Depending on the geographic dispersion of
the locations, adding an extra transmission
facility to complete the ring may be cost
prohibitive
Rings are not very scalable
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Star topology
Have connections to networked devices
that “radiate” out form a common point
 Each networked device in star topology
can access the media independently
 Have become the dominant topology type
in contemporary LANs
 Stars have made buses and rings obsolete
in LAN topologies

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Star topology
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Advantages of star topology
1)
2)
3)
4)
Compared to Bus topology it gives far
much better performance
Easy to connect new nodes or devices
Centralized management. It helps in
monitoring the network
Failure of one node or link doesn’t affect
the rest of network
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Disadvantages of star topology
1)
2)
3)
If central device fails whole network
goes down
The use of hub, a router or a switch as
central device increases the overall cost
of the network
Performance and as well number of
nodes which can be added in such
topology is depended on capacity of
central device
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Peer-to-peer
User Location A
T1
T1
User Location B
User Location C
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Advantage/Disadvantage of Peer-topeer

Advantage:
It is inexpensive relative to other options

Disadvantages:
They don’t scale very well. As additional
locations are introduced to the WAN, the
number of hops between any given pair of
locations remains highly inconsistent and has
an upward trend
An equipment or facility failure anywhere in a
peer-to-peer WAN can split the WAN
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Star network Topology
constructed by homing all locations into a
common location
 The star topology can be constructed
using almost any dedicated transmission
facility including frame relay and point-topoint private lines

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Advantages/Disadvantages of star
topology

Advantages:
More scalable than a peer-to-peer or ring
network
Improved network performance. Hop count
of three

Disadvantages:
It creates a single point of failure
There is no route redundancy
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Star topology
User Location A
T1
T1
T1
User Location C
User Location B
User Location D
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Mesh topologies

A network setup where each computer and
network device is interconnected with one
another, allowing for most transmissions to
be distributed, even if one of the
connections go down. This topology is not
commonly used for most computer
networks as it is difficult and expensive to
have redundant connection to every
computer.
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Mesh topologies

However, this topology is commonly used
for wireless networks. Below is a visual
example of a simple computer setup on a
network using a mesh topology.
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Advantages of Mesh topologies
They use dedicated links so each link can
only carry its own data load. So traffic
problem can be avoided.
 It is robust. If any one link get damaged it
cannot affect others.
 It gives privacy and security.(Message travels
along a dedicated link)
 Fault identification and fault isolation are
easy.

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Disadvantages of Mesh topologies
The amount of cabling and the number of
I/O ports required are very large. Since
every device is connected to each devices
through dedicated links.
 The sheer bulk of wiring is larger then the
available space.
 Hardware required to connected each
device is highly expensive.

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Hybrid topologies
Hybridization of multiple topologies is useful
in larger, more complex networks
 Multitiered networks, in particular, lend
themselves to hybridization. A multitiered
WAN can be hybridized by fully or partially
meshing the backbone tier of routers
 An effective hybrid topology may be
developed in a multitiered WAN by using a
fully meshed topology for the backbone
nodes only

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Hybrid topology
T3
T3
T3
Backbone tier
T1
T1
T1
User Location D
User Location B
56Kb
T1
56Kb
Concentrator tier
T1
T1
User Location C
User Tier
User Location E
User Location F
User Location G
User Location H
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Hierarchical combinations
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Considerations for choosing a
topology
Money-Bus n/w may be the least expensive
way to install a n/w.
 Length-of cable needed- the linear bus n/w
uses shorter lengths of cable.
 Future growth-with star topology, expending
a n/w is easily done by adding another
devices.
 Cable type-most common used cable in
commercial organization is twisted pair.
Which often used with star topologies.

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Case Study – Network Design
You are asked to develop plans for a new
network.
 The following parameters are associated with
this project:
◦ There are 20 users, each requiring need to
print to a common laser printer. They use
word-processing and spreadsheet
applications. They also will regularly access a
specialized database application that draws
data from a common file.
◦ The company expects to add 10 new users in
the next 12 months.

Case Study – Network Design
Required results:
◦ Provide a flexible network solution at a
reasonable cost.
◦ Choose between peer to peer and client
server network : depends on the suitability.
 Optional results:
◦ Network should be easily administered
◦ Provide security for files across the network
◦ Reliability and good performance of network
should be justified.