ETHERNET

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ETHERNET

• Ashish Babbar
• Ramkumar Gowrishankar

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OVERVIEW

• Introduction to Ethernet
• CSMA/CD
• Network Configuration
• Simulation Parameters
• Result
• Conclusion

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INTRODUCTION TO ETHERNET

• Ethernet is one of the most widely used network
  topologies for Local Area Network
• Popular because it is cheap, easy to set up and
  use and very fast
• Standard Ethernet operates at 10Mbps, fast
  Ethernet operates at 100 Mbps, and latest gigabit
  Ethernet operates 100 times faster than standard
  Ethernet
• Uses CSMA/CD to share a common bus among several
  users
• Network Utilization is an instantaneous
  measurement of the ratio between the number of
  bits transmitted in a given period, such as one
  second, divided by the network capacity.

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CSMA/CD

• Carrier Sense Multiple Access/Collision Detection
  is the mechanism used by Ethernet to share a
  common bus between multiple users
• Carrier sense implies that all nodes can
  distinguish between an idle and busy link
• Collision detection implies that a node keeps
  listening to the medium even when it is
  transmitting in order to detect when a frame it
  is transmitting has collided with a frame from
  another node.

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LAB OBJECTIVE

• To demonstrate the operation of the Ethernet
  Network and examine the performance of the
  ethernet under different scenarios.
• To study how the throughput of the network is
  affected by
• the network load
• Number of nodes in the network
• the size of the packets.
• Utilization of the bus

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NETWORK CONFIGURATION

• Ethernet with 30 nodes is connected via co-axial
  link in a bus topology
• Co-axial link is operating at a data rate of 10
  Mbps
• Network is set up in an office of area 200m100m
• Nodes are connected to the bus via ethernet bus
  tap

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NETWORK CONFIGURATION (contd.)

• Propagation delay is 0.05 sec/m
• A higher delay can be used as an alternative to
  generating a higher traffic which would need
  longer simulation time
• ON State time exponential(100)
• OFF State timeexponential(0)
• Packet size1024 bytes
• Inter-arrival time set in each simulation to vary
  the offered load
• Simulation time15 seconds

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SNAP SHOT OF NODE ATTRIBUTES
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NETWORK SNAPSHOT
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SIMULATIONS EXECUTED

• Relation between received (throughput) and sent
  (load) packets
• Mean inter-arrival times used are 2, 1, 0.5,
  0.25, 0.1, 0.05, 0.035, 0.03, 0.02
• Simulation run time15 seconds
• Output Throughput vs. load graph
• Average traffic received vs. time (plotted for
  different inter-arrival times)
• Mean inter-arrival times chosen are 0.1, 0.085,
  0.065, 0.05, 0.035, 0.025, 0.022, 0.02
• Simulation time 100 seconds
• Output Average network throughput, Average
  number of collisions, Bus Utilization

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SIMULATIONS EXECUTED (contd.)

• Effect of number of nodes on the number of
  collisions in the network
• Number of nodes reduced to 15 from 30 and also a
  23 node network was simulated
• Simulation time30 seconds
• Effect of packet size on the traffic received
• Packet size changed from 1024 bytes to 512 bytes
• Simulation time50 seconds
• Traffic received in bits/ sec and packets/sec
  measured and plotted

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RESULTS

• The graph is the traffic received (throughput)
  vs. traffic sent (load)
• Initially throughput increases with offered load
  and achieves an optimum value
• After the optimum load any further load only
  leads to decrease in the throughput
• Thus in order to maximize the throughput the load
  must be chosen carefully

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RESULTS (contd.)

• Legend
• Coax1a0.1 s
• Coax1b0.085 s
• Coax1c0.065 s
• Coax1d0.05 s
• Coax1e0.035 s
• Coax1g0.025 s
• Coax1h0.022 s
• Coax1i0.02 s

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RESULTS (contd.)
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RESULT (contd.)(Bus Utilization)
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RESULTS (contd.)

• Both graphs reveal that for given inter-arrival
  time average throughput and average number of
  collisions become constant, i.e., the network
  stabilizes
• The throughput graph shows that with decreasing
  inter-arrival times the throughput increases till
  a certain maximum throughput is reached and then
  decreases
• This reveals a band of acceptable inter-arrival
  times in which the throughput is not severely
  degraded
• The average number of collisions indicates that
  as long as the inter-arrival time is within a
  given limit the number of collisions are not too
  much, but once the critical threshold is reached
  the number of collisions increases dramatically

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RESULTS (contd.)

• Graph shows the number of collision for a 30
  node, 23 node and 15 node network
• Coax1f denotes the 30 node network and Coax2f
  denotes the 23 node network and Coax2f1 denotes
  the 15 node network
• It is seen that as the number of nodes in the
  network increases the number of collisions
  increases

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RESULTS (contd.)

• Time average of packets received/sec is plotted
  for packet size of 1024 bytes (Coax1f) and packet
  size of 512 bytes (Coax3f)
• The throughput for the 512 byte packet is greater
  than that for the 1024 byte packet

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RESULTS (contd.)

• Time average of bits received/sec for both packet
  sizes is shown
• The Coax3f network has higher bit throughput than
  the Coax1f network

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CONCLUSIONS

• The operation of the Ethernet network was studied
  
• Results showed that an Ethernet network has an
  optimum throughput only under certain load
  conditions
• The throughput is not optimum in the case when
  the network load is low or the case where the
  network load is too high
• It was also seen that greater the number of nodes
  in the network greater the number of collisions
• The effect of packet size on the collisions in
  the network and also the network throughput was
  studied and it was found that smaller size
  packets are better than larger size packets

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