Computer network design

COMPUTER NETWORK DESIGN

OBJECTIVE:

To exhibit the implementation of Switched Lan using OPNET. The simulation will make us understand different implementations in Local Area Networks using Hubs and Switches.

SUMMARY :

Hubs and Switches are the two different types of devices used in a Switched LAN setup. The most essential part of any network are the Switches. Generally the hubs transmit all the received packets to all of its ports and other hosts. A collision occurs when other host tries to send packets. The packets received by the switches are forwarded to other outputs and the destination address of the packet is read from the header in the packet. As the speed variates in the network, the switch buffers its packets and then discards the packets when the buffer space is filled. In this project we deal with Traffic Sent, Traffic Received and the Delay between the ports.

BUILDING A HUB NETWORK:

Creating a New Network:

  1. Open OPNET IT GURU EDITION and Select NEW FILE.
  2. Rename the project name as LAB1_SWITCHEDLAN and scenario as ONLY HUB.
  3. Select Create Empty Scenerio in the Initial Topology dialog box.
  4. Click Next & Choose Office from Network Scale list - Click Next - Click OK and proceed.
  5. Network Initialization:

  6. Select Topology Rapid Config Star OK.
  7. Click Select Models and from the Model List Menu select Ethernet.
  8. Set Center Node Model - Ethernet16_Hub.
  9. Set Periphery Node Model Ethernet_Station.
  10. Set Link Model - 10BaseT and No = 16.
  11. Set X = 50 Y = 50 and Radius = 42
  12. Network Configuration:

  13. Right Click on one of the nodes and Select Similar Nodes.
  14. Right Click on the Hub- Edit Attributes- Rename as Hub1.
  15. Expand Traffic Generation Parameters and Packet Generation Argument.
  16. Change ON State Time to 100.0
  17. Change OFF State Time to 0.0
  18. Change Inter Arrival Time to 0.02
  19. Change Packet Size to constant 1500- Click OK
  20. Choosing Statistics:

  21. Select Simulation Tab - Choose Individual Statistics.
  22. Expand Global Statistics - Ethernet - Delay.
  23. Expand Traffic Sink - Traffic Received.
  24. Expand Traffic Source - Traffic Sent.
  25. Expand Node Statistics - Ethernet - Collision Count.
  26. Simulation:

  27. Run the Simulation by clicking on
  28. Set Duration as 2.0 Minutes - Click OK.

BUILDING OF HUB AND SWITCH NETWORK:

A new network containing both Hub and Switch is created for better comparison of Only Hub and Hub and Switch Network.

Duplicating The Scenario:

  1. From the Scenario Menu Select - Duplicate Scenario - Rename as HubAndSwitch.
  2. Click on the Object Pallete Button .
  3. Drag and Drop Ethernet16_Hub and Ethernet16_Switch from the Object Palette on to the work station.
  4. To confirm the connection Right Click on the Work Station.
  5. Right Click on New Hub - Edit Attributes - Rename to Hub2 - Click OK.
  6. Right Click on switch - Edit Attributes - Rename to Switch - Click OK.
  7. The HubAndSwitch network must be Rearranged.
  8. Run the Simulation:

  9. Select Manage Scenarios from Scenarios Menu.
  10. Values under Results column must be changed to ⟨collect⟩ (or ⟨recollect⟩) for both scenarios.
  11. Run the Simulations.
  12. Results:

  13. From Results Menu select Compare Results.
  14. Change As Is to Time_Average.

ANALYSIS OF SWITCHED LAN:

Tests are done and compared for the following scenerios:

  1. Only Hub
  2. Hub And Switch

TRAFFIC SENT:

If the bandwidth is not used completely, it shows that traffic sent in packets/sec is low. And if traffic sent in packets/sec is high collision occurs resulting in the dropping of throughput.

Comparisons:

The curve in Fig 3 shows that both are same and no change can be seen in any networks.

TRAFFIC RECEIVED:

A 10 Base T link is used which helps in sending or receiving maximum no of packets/sec without any collision. A total of 821 packets are sent. From the graph we observe that traffic sent is more compared to the traffic received due to collision.

Comparisons:

A HubAndSwitch divides a network into two domains as seen in Fig 2 which reduces the no of collisions. Whereas in a Hub it basically results in more collisions. The above fig shows that the traffic received when the hub is used is 710packets/sec and 775packets /sec when both Hub and Switch are used.

DELAY:

The amount of time taken by a packet to reach a point is called Ethernet Delay. If a packet is idle, the host recognizes it and transmits the packets immediately. The process is put in a halt abruptly when collision occurs. Generally the host uses a CSMA/CD for transmission.

Comparisons:

Delay depends on the no of collisions by the time it reaches the final point . Delay increases ddue to more collisions in the Hub. Where as in HubandSwitch the collision domain is done separately so the delay decreases and collisions are also less. From the graph we observe that the Delay is 0.171 when OnlyHub is used and 0.011 when HubAndSwitch is used.

COLLISION COUNT IN HUB1 AND HUB2:

HUB 1:

In Fig 2 we see that the hub has 16 nodes and hubandswitch has 8 nodes each.Due to this the collisions are more on OnlyHub compared to HubandSwitch.And from Fig6 we conclude that collisions in Only Hub is 2392 per sec and in HubAndSwitch it is 902.32 per sec.

HUB 2:

We observe that the no of collisions are 907.15 per sec which is very near to the collisions found in Hub 1.

COMBINED COLLISION COUNT:

A Switch is generally used over a hub to make a network faster. And it also decreases the collision rate. So we see in the graph that the collisions in OnlyHub is 2392 per secand HubAndSwitch is 902.32 per sec.

Questions:

1. Explain why adding a switch makes the network perform better in terms of throughput and delay.

We see in the graph that adding a switch decreases the delay and increases the throughput. If two frames arrive at the same time, it causes a collision and the entire hub will create a single collision domain. All the lines entering a hub must operate at the same speed .In only hub scenario, there is only one hub and 16 hosts and for all the hosts there is one collision domain. So the number of collisions is more and therefore no. of retransmissions is higher. Addition of a switch divides the network in two collision domains of 8 hosts, with one hub in each domain. So the no. the number of collision decreases. Collision is directly related to delay. Delay is the time taken for end to end delivery of all packets. If there is less no. of collisions then there will be less no. of retransmissions and the packets will deliver early and delay will be less. Throughput is the no. of packets received, by the destination hosts, per second. This also depends on collision. If there is less no. of collisions then the no. of received packets will increase per second. The result is the increase in throughput.

2. We analyzed the collision counts of the hubs. Can you analyze the collision count of the "Switch"? Explain your answer

Hubs have single collision domain for all the hosts which are connected to it. Switches have different collision domains for all the hosts. So there is no collision in switches. Switches forward the frames to the appropriate port according to the frame's destination address. Switches buffer the frames if sender's speed is higher than its own speed and when buffer goes full it discards the frame. There is no loss of frames because of collision.

3. Create two new scenarios. The first one is the same as the Only Hub scenario but replace the hub with a switch. The second new scenario is the same as the HubAndSwitch scenario but replaces both hubs with two switches, remove the old switch, and connect the two switches you just added together with a 10BaseT link. Compare the performance of the four scenarios in terms of delay, throughput, and collision count. Analyze the results.

Note: To replace a hub with a switch, right-click on the hub and assign ethernet16_switch to its model attribute.

BUILDING OF ONLYSWITCH NETWORK:

Creating a New Network:

  1. Click NewScenario as ONLY SWITCH.
  2. Select Create Empty Scenerio in the Initial Topology dialog box.
  3. Click Next - Choose Office from Network Scale list - Click Next - Click OK and proceed.
  4. Network Initialization:

  5. Select TopologyRapid ConfigStarOK.
  6. Click Select Models and from the Model List Menu select Ethernet.
  7. Set Center Node Model - Ethernet16_Switch.
  8. Set Periphery Node Model - Ethernet_Station.
  9. Set Link Model - 10BaseT and No = 16.
  10. Set X = 50 Y = 50 and Radius = 42

Network Configuration:

  1. Right Click on one of the nodes and Select Similar Nodes.
  2. Right Click on the Hub- Edit Attributes- Rename as Switch1.
  3. Expand Traffic Generation Parameters and Packet Generation Argument.
  4. Change ON State Time to 100.0
  5. Change OFF State Time to 0.0
  6. Change Inter Arrival Time to 0.02
  7. Change Packet Size to constant 1500- Click OK
  8. Choosing Statistics:

  9. Select Simulation Tab - Choose Individual Statistics.
  10. Expand Global Statistics - Ethernet - Delay.
  11. Expand Traffic Sink - Traffic Received.
  12. Expand Traffic Source - Traffic Sent.
  13. Expand Node Statistics - Ethernet - Collision Count.
  14. Simulation:

  15. Run the Simulation by clicking on
  16. Set Duration as 2.0 Minutes - Click OK.

BUILDING OF SWITCH AND SWITCH NETWORK:

A new network containing Switch and Switch is created for better comparison of Only Switch and SwitchAndSwitch Network.

Duplicating The Scenario:

  1. From the Scenario Menu Select - Duplicate Scenario - Rename as SwitchAndSwitch.
  2. Click on the Object Pallete Button .
  3. Drag and Drop Ethernet16_Switch from the Object Palette on to the work station.
  4. To confirm the connection Right Click on the Work Station.
  5. Right Click on New Switch - Edit Attributes - Rename to Switch2 - Click OK.
  6. Right Click on switch - Edit Attributes - Rename to Switch - Click OK.
  7. The SwitchAndSwitch network must be Rearranged.

Run the Simulation:

  1. Select Manage Scenarios from Scenarios Menu.
  2. Values under Results column must be changed to ⟨collect⟩ (or ⟨recollect⟩) for both scenarios.
  3. Run the Simulations.
  4. Results:

  5. From Results Menu select Compare Results.
  6. Change As Is to Time_Average
  7. TRAFFIC SENT:

    As we observe in the graph below that traffic sent is 773packets/sec and it also shows that there is no change even if the Hub is replaced by a Switch as long as it has the same no of Nodes connected to them individually and sent at same rate in every scenario.

    TRAFFIC RECEIVED:

    We observe in the graph below that the traffic Received when OnlyHub is used is 710packets/sec and 775packets/sec when Hub and switches are used which shows that the traffic increased when switches are replaced with hubs.

    DELAY :

    The graph below shows that when OnlyHub is used the delay is 0.171sec , 0.011sec when HubAndSwitch is used, and 0.003sec when only switch is used. Here the delay gradually decreases and when Switch and switch is used there are no collisions and the delay is known as propagation delay.

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