Local Area Networks Interconnection

This lab is designed to demonstrate the implementation of switched local area networks. The simulation in this lab can help you examine the performance of different implementations of local area networks linked by switches and hubs.

A hub forwards the packet that arrives on some of its inputs on all the outputs whatever the destination of the packet. Hub has only 1 collision domain.

On the other hand, a switch forwards incoming packets to 1 or more outputs with respect to the destination(s) of the packets. Switches has separate collision domains for every connection.

Here we will study how the throughput and collision of packets in a switched network are damaged by the configuration of the network and the types of switching devices that are used.

Implementation of Network

The implementation involves series of steps the following

We select the network topology as star and edit all the attributes as per the lab manual.

The next step is to configure the nodes of the network for setting the traffic made by each station. The network includes 16 nodes each which is linked to a hub by way of a 10 Base-T Ethernet.

The statistics are chosen for the simulation. We choose the delay(sec), traffic sent ( packets/sec), traffic received ( packets/sec) and the collision count.

The simulation is configured for the time duration of 2 minutes.

The next step involves duplicating the scenario to be able to get two hubs linked by one switch.

Finally, the simulation is run and the email address details are compared for their performance predicated on the statistics chosen for simulation.

Lab Results:

We have attempted two scenarios i. e.

Scenario1: Only hub

Scenario2: Two hubs and a switch.

The statistics chosen for comparing the above mentioned scenarios are

Ethernet Delay (sec)

Traffic sent (packets/sec)

Traffic received (packets/sec)

Collision count.

As per the implementation steps followed, we received the next results listed below

The two figures given below compares the traffic sent/received(packets/sec) in both scenarios.

The Fig#1 indicates that the common time to send the info packets in a network with a hub or a hub & switch is the same or almost identical.

The Fig#2 indicates that the common time to get data packets or the throughput in case there is a hub & switch network is more than that of a network with only hub.

Fig1. Indicates enough time average for traffic submitted packets/sec

Fig2. Indicates enough time average for traffic received in packets/sec

The two figures listed below compares the collision count and the time delay in both scenarios.

The Fig#3 indicates that the collision count in a hub and switch network is lesser than within an only hub network.

The Fig#4 indicates that Ethernet delay in a hub and switch network is lesser than in an only hub network.

Fig3. Indicates Ethernet collision count for both scenarios

Fig 4. Indicates Ethernet delay(sec) for both scenarios.

The Fig#5, compares the collision count in both the scenarios i. e. with only Hub and in Hub&Switch networks.

It implies that the collision count for only Hub is maximum when compared with the collision count for a Hub&Switch network.

The collision count for the Hub1 and Hub2 in the office network have almost the same collision rate.

Thus, it proves that the collision rate reduces in a network with a switch compared to the network with a hub. Thus, the throughput of switched network is greater than only hub networks.

Fig 5. Indicates the collision count of the Hub in the Only Hub network and the Hub1 and Hub used in the Hub and Switch network.

Question and Answers

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

Ans: According to the collision count identified for both network with only Hub and other with a Hub & Switch, the collision count for the Hub1 and Hub 2 in a switched network is much lesser than the Hub1 in the one Hub network. This happens due to following reasons

As soon as the Hub receives the packets at its input ports, it forwards them to all outputs regardless of the destination of the packet to be sent. This increases the chances of collision in hubs.

Where as, in case there is a switched network, the switch can receive the packets at its input ports in parallel, and forwards multiple packets with their destined addresses at exactly the same time.

In the lab experiment, there exists two hubs i. e. Hub1 and Hub2 with a switch connecting the two in the middle. Both hubs receive the packets. The switch acts a a mediator between your two hubs and forwards the packets from one hub to the other with lesser collision.

Thus, the switch really helps to decrease the collision rate in comparison to that with a single hub. Hence, this boosts the network performance in conditions of throughput and delay.

Q 2 We analyzed the collision counts of the hubs. Is it possible to analyze the collision count of the "Switch? Explain your answer.

Ans: Inside the experiment, we have analyzed the collision counts of the hubs in both single and double hubs with a switch networks. Through the results from the experiment, it clears tha undeniable fact that the collision count by using a switch reduces to a larger amount compared to that with out a switch. This is because of the fact, that the switch can have the packets in parallel and buffer the same in case there is heavy incoming traffic and also forward the same in parallel with their destined address. Since, there's always a full duplex communication between the switch and the hub, thus the packets exchanged will never collide with each other. Thus, there are almost no collisions in case there is switch.

Q 3 Create two new scenarios. The first one is equivalent to 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, take away the old switch, and connect the two switches you just added as well as a 10BaseT link. Compare the performance of the four scenarios in conditions 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.


In the first scenario we have duplicated the scenario consisting of only a hub.

Thus, really the only hub shown in Fig3. 1 has been replaced by way of a switch as shown in Fig3. 2.

In the second scenario, we've duplicated the network with Hub and a switch as shown in Fig#8.

Thus, the two hubs in Fig3. 3 have been replaced by two switches and have removed the older switch as shown in Fig3. 4. Both the new switches have been linked using a 10 BaseT link.

Fig 3. 1 N/W configuration with only hub.

Fig 3. 2: N/W configuration with only switch.

Fig 3. 3 N/W configuration with two hubs and one switch

Fig3. 4 N/W configuration with two switches

Comparing the Results:

The four scenarios which have been compared are the following

(1) Network with only a hub

(2) Network with a Switch and a Hub

(3) Network with only a switch

(4) Network with two switches.

In the Fig3. 5, the graph compares the Ethernet delay in seconds for all your four scenarios. It shows, that enough time delay is maximum for a network with an individual hub and least for networks without hubs but switch(s). Thus, the graph demonstrates the time delay reduces with the number of switches added in the network

The Fig3. 6 compares the throughput i. e. the amount of packets received per seconds for all your four scenarios. According to the graph, the throughput is almost the same and maximum for the networks comprising one or two switches. Whereas, the throughput is less with only hub in the network. Thus, the no. of packets received is greater for the networks that are switched based.

Fig 3. 5 Compares the Ethernet delay in sec for four scenarios.

Fig3. 6 Compares the traffic received (Throughput) in packets/ sec for the four scenarios.

We have not compared the collision count for the four scenarios because the collision count is very less in case of switched networks.


From this lab experiment we've figured the switched networks have better throughput, delay and collisions compared to the network with Hubs. The difficulty faced while performing the experiment was the reading of collision count for the switched network with two hubs and the switch in middle. We faced issues in collecting the combined results of collision for the first two scenarios.

But towards the finish of the lab experiment, we received good practical experience on Opnet, and the features of using a switched network in comparison to hubs.

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