The document details a lab experiment comparing the performance of networks utilizing hubs versus switches. It concludes that switches significantly improve network performance in terms of throughput, delay, and collision counts, as they can route packets more efficiently and allocate dedicated bandwidth to each node. The analysis shows that while both scenarios send the same amount of traffic, systems with switches show higher received traffic and lower delays and collisions compared to those with only hubs.

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Opnet Lab 3 Solutions
Switched LANs
A Set of Local Area Networks Interconnected by Switches
Haider Nafaa Nseif
ID:I201521051
18/12/2017
IRAQ

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Result After successfully running the simulation for the HubOnly & HubAndSwitch
1) The buffer switching :
The buffer space at the switching nodes efficiently while giving each user a fair share of the
network bandwidth under both light traffic and heavy traffic conditions. The switch reduce
delay also has a table for all its nodes attached to it to that it's faster than the Hub. The
result of the delay in the HubOnly is greater than the delay in HubAndSwitch.
The Delay
2) Traffic Received Delay Comparing and Analyzing the Result for HubOnly and
HubAndSwitch :
The switches save bandwidth than the hubs. When a switch is first connected to the network, it doesn't know
anything about the network. Without any knowledge, it has to flood every packet it receives onto every port,
behaving in effectively the same way as a hub would. However, the switch can learn from each packet it sees, and
this means it can make better decisions and due less packet loss. To that we shows that the packets received or
delivered are more when a switched is attached in the topology than when only Hub is used.

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The Traffic Received (packet/sec)
3) Comparing and Analyzing the Result for HubOnly and HubAndSwitch Analysis:
A) Traffic Sent
The traffic sent is same in both cases they're sending the same amount of packets.
The Traffic Sent (packet/sec)

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B) The Collision count
In the OnlyHub scenario when the Hub receives a packet in one node, it will redirect
that packet to all other nodes (flood broadcast message), because the hub does not
know the destination address. This leads to increase collision count ,while adding a
Switch in the HubAndSwitch scenario will increasing the bandwidth for each of the
node and this will reduce the collision count as each node as more bandwidth in
compare to Hub. Because Switch will send the received data packet to the dedicated
line from all other nodes, this functionality of Switch helps in increasing the
throughput. Another important constraint for any network is Collision Count. All the
nodes connected to the hub share the bandwidth among them, while in switch
nodes have the full bandwidth. So by adding a Switch in a network we are increasing
the bandwidth for each of the node and this will reduce the collision count as each
node as more bandwidth.
The Collision Count Hub1
The Collision Count Hub2

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The Collision Count 2 Scenario
Question / Answer:
1) Explain why adding a switch makes the network perform better in terms of throughput
and delay.
Hub forwards the packet to all its connection without taking consideration of
addressing for packet transfer. Such it will send a packet to its all link. Apart from
this, there is no traffic inspection and it will just forward the packet. This is very
inefficient way of communication. Hub is also not self configured device. So there is
always a starting delay.
Switch is a smart network device compare to hub. It serves the several dedicated links
independent to each other. This feature improves the throughput of the network.
Switch is self configured device so network downtime is less and received packet will
be sent to its destination only on bases of its address. This characteristic of switch
reduces the delay.
So when we add a switch in our second scenario, traffic generated at any node will be
directed to its destination node. So there is no traffic propagation. Such switch makes the
network performance better in terms of throughput and delay.

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2) We analyzed the collision counts of the hubs. Can you analyze the collision count of
the “Switch”? Explain your answer.
Hubs are "shared media" and switches are not. We cannot analyze the collision count
of the Switch.
Switch will divides the network into multiple segments and maintain simultaneous
connection of multiple pairs of the computer which do not compete with other pairs of
computers for network bandwidth . When switch receives the packet it will forward the
packet to its destination using the information of destination address in a header. So in
Switch each port has its designated bandwidth. Multiple connections can be handle
separately using switch. As Switch does not share the transmission media, network do not
experience collision.
3) Create two new scenarios. The first one is the same as the OnlyHub scenario but
replace the hub with a switch. The second new scenario is the same as the
HubAndSwitch scenario but replace 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.
A) The packets sent :
Traffic Sent for all four scenarios is identical. There is no big difference among them.
The packets sent are almost the same in all the topologies because they are generated from
the nodes which have nothing to cause packet loss from the point of generation.

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Figure 9: Traffic Sent for all Four Scenarios.
B) The Packets Received:
It can be seen in Figure 10 that traffic received is high in scenarios where Switch is present.
This proves that Switch improves the throughput of the network.
Figure 10: Traffic Received in all Four Scenarios.

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C) The Delay
When we compare the delay for all four scenarios, following result came as shown in Figure
11. It can be seen that Switches reduce the delay in network as it as self configured device
and use dedicated bandwidth for each nodes. When there is only hub in a network, delay is
high compare to the network with switches.
Figure 11: Delay for all Four Scenarios.
D) The Collision Count :
Figure 12 shows the result for comparison of Collision count of all four scenarios. It can be
seen from the graph that collision count for OnlyHub scenario is higher than any other
scenario. As we add a Switch with hub, Collision count is decreased. There is no Collision
Count for scenarios where only switches are used because switch does not share the
transferring media among nodes.
Figure 12: Collision Count for all Four Scenarios

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Conclusion:
By performing this laboratory we learned that how different devices used in a network
affects the performance of the network in terms of throughput, delay and collision.
We also learned that Switch is better network device than hub as it improves the
performance of the network. We learned that use of switch in implementation of a
network will reduce the collision and delay, and increase the throughput.