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COMPUTER NETWORKS LAB 3

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					  COMPUTER NETWORKS
LAB 3: HUBS AND SWITCHES



     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




                                                     4
HUBS:
   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.


                                                    5
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.


                                              7
Only HUB Scenario:




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Hub and Switch Scenario:




                           10
Manage Scenarios:




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Compare Results:




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Graph for TRAFFIC SENT:




                          13
Graphs for PACKETS RECEIVED:




                               14
Graph for DELAY:




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Graph for COLLISION COUNT:




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POSSIBLE QUESTIONS:
   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.


                                                   18
POSSIBLE QUESTIONS:
   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:
   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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