COMPUTER NETWORKS LAB 3

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COMPUTER NETWORKS
LAB 3: HUBS AND SWITCHES
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RAJESH KATRAGADDA
BHARATH NADELLA
SHIVANANDAN GOUD KOMMURI
SRIDHARA PRUDHVI DUTH POTLURI
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SWITCHES:
A switch is a multi-input, multi-output device
which transfers packets from an input to one
or more outputs.
 Switch is basically a star topology having
features like
a. Large
networks
can
be
built
by
interconnecting a number of switches
b. Adding new host to network by connecting it
to a switch does not necessarily reduce the
performance of the network for other hosts
already connected.

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APPROACH:
Switch makes use of header of the packet for
an identifier to trace the destination.
 Basically three approaches used are
a. Datagram or connectionless (data transfer
only)
b. Virtual
circuit
or
connection-oriented
(connection setup and data transfer)
c. Source routing
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HUBS:
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A hub joins multiple computers (or other
network devices) together to form a single
network segment. On this network segment,
all computers can communicate directly with
each other.
Hubs do not read any of the data passing
through them and are not aware of their
source or destination. It just broadcasts the
packets out to all devices on the network including the one that originally sent the
packet.
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TYPES OF HUBS:
Three different types of hubs exist
a. Passive : do not amplify the electrical signal
of incoming packets before broadcasting
them out to the network.
b. Active : amplify the electrical signal of
incoming packets before broadcasting them
out to the network.
c. Intelligent : add extra features to an active
hub that are of particular importance to
businesses.

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AIM:
This lab demonstrates the implementation of
switched local area networks.
The simulation in this lab will help us to
examine the performance of different
implementations of local area networks
connected by switches and hubs.
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Only HUB Scenario:
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Hub and Switch Scenario:
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Manage Scenarios:
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Compare Results:
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Graph for TRAFFIC SENT:
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Graphs for PACKETS RECEIVED:
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Graph for DELAY:
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Graph for COLLISION COUNT:
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POSSIBLE QUESTIONS:
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Explain why adding a switch makes the
network perform better in terms of
throughput and delay
ANS: Unlike hubs, Switches Buffer the frames
reaching it. So Switches share the bandwidth
equally among all the nodes and maintains
address tables to forward frames. Hence it
leads to better performance in terms of
throughput and delay.
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POSSIBLE QUESTIONS:

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We analyzed the collision counts of the hubs.
Can you analyze the collision count of the
switch?
ANS: As hubs don’t look at the destination
address of the frames reaching it and just
forwards them to all other nodes, there is
collision count for Hubs. But in case of
Switches, it look at the destination address
and buffer the frames and send them
according to the address table. So Switches
have no Collisions, so no Collision Count.
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Only SWITCHES Scenario:
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Graph for DELAY:
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Graph for TRAFFIC RECEIVED:
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Graph for TRAFFIC SENT:
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CONCLUSION:
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From above Graph for DELAY, its clear that
delay for Only Hub Scenario (Blue) is pretty
high and for Hub and Switch Scenario (Red) it
is significantly low compared with Only Hub
Scenario. But the Delay for Hub and Switch
Scenario and Only Switches Scenario (Green)
is not that significantly different, as in the
earlier case.
More over as Switches cost more than hubs,
Its better to use a Hub and Switch
combination in the network than only Switch
or only Hub combination.
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