Switched based ethernet local area networks (LAN) are network cables which uses switches while connecting to other networks or segments. the switch acts as repeater for the case of individual network hosts. The ethernet switch allocates the device full network based on the speed of the host [1]. The switched based networks are sometimes called desktop ethernet networks.
When segments are used, hubs are substituted to switching hubs. Switch based networks are an improvement of traditional ethernets through which devices compete for one common host. the switch based local area networks are currently taking the market because of their advantages, they increase the bandwidth of the existing networks. For hub network configuration however, several devices are connected to one central point. Some devices use a switch or a router instead of a hub [8]. Figure 1 show hub network topology [6]. When a packet is received it the hub, it is broadcasted to all other devices connected to the hub thus all of them receive the package at the same time with the possibility of collision [3][4]. However, switched based ethernets may be used to prevent occurrence of any collision.
2.1 Objectives
The objectives of this experiment were as stated below
2.2 Model description
The Ethernet LAN simulation model implements a client server application, where host 0 is the server and rest of the terminals are clients. Clients will send requests in the form of Ethernet packets to obtain a reply from the server. Total traffic flow in the network will be twice the number of packets generated by all client terminals in the network. Client and server packet sizes are selectable from the omnetpp.ini file. Simulation parameters are listed in the table 1 below.
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Simulation Parameters |
Value |
|
|
Transmission rate: R |
10 Mbits/sec |
|
|
Simulation length |
300 sec |
|
|
Packet length: L |
Client: 200B, Server: 800B (Simulation 1) Client: 200B, Server: 1200B (Simulation 2) |
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|
Simulation No. |
Simulation Parameters |
Results to collect |
|
Scalar |
||
|
1 |
No of clients: 5, server: 1, (number is in *.ini file). Traffic load: 50, 75, 100, 125, 150, 175, 200 packets/sec/node. Run simulation for both Hub and Switched network models. |
Mean end-to-end client packet delay, Rx channel utilisation and Rx channel collision, Send & receive packets (mac layer) |
|
2 |
Change the server packet length to 1200B. Calculate the traffic load in packets/sec to generate same amount of load as simulation 1. For example, for 1200B packet size 35.7 packets/sec will generate same load as 50 packets/sec using 800B packet size. |
As above |
2.3 Procedure
The previously developed OMNET++ simulation models found in the ELEC3500 folder were utilized in this experiment. By selecting a model in the run window, the model was run both in the Hub and switched LAN mode. In cases of Bus configurations mode, the comments of the bus networks were made to reduce the initial start time.
Using the Hub and switched network model configurations made above, the simulation 1 and 2 below were performed. Parameters used for simulation were as shown on table 1 and 2 under the model description.
For simulation 1, scalar data was obtained from tables 1 and 2, this was needed to plot mean packet delay, channel utilisation, collision utilisation and packet delivery ratio against the traffic load for both networks. The packet delivery ratio was defined as the ratio of number of packets received from the server to the request packets to server from client. All models developed in this case ensured that every node transmitting request packet received a packet back from server.
For simulation 2, the packet length was changed and the traffic load set as that of simulation 1. This simulation was to evaluate the effects of increasing the packet length on performance of networks.
1.0 Results and discussion
The results for the above experiment were represented in graphical plots using MATLAB, the figures 3,4,5,6 represents the results.
Consider the load vs delay and load vs packet delivery ratio plots for simulation no. 1 & 2. Use plots for both Hub and Switch networks. Considering these plots identify the similarities and differences between the hub and switch networks. Explain why one of the networks introduced higher packet delay and higher packet delivery ratio.
From the plotted graphs, there is much similarities between the hub and switched ethernet LAN configuration as compared to the differences. The response is almost linear for both Hub and switched ethernet LAN.
The differences in delays of packet delivery between the hub and switch networks Can be explained by the fact that Hub always perform flooding in its broadcasting, and may exhibit both unicast and multitask networking, the switch networks performs the broadcasting first, then the unicast and multicast of packets will depend on the feedback from the client.
Consider the Rx channel utilisation plots for simulation 1 and 2 for both networks. Explain how the packet length influences the collision levels in the hub network. Explain possible reason for different results.
A packet is generally a single unit that is transferred over time. A small packet length will take a shorter time to be transmitted thus resulting to a smaller number of collisions as compared to a packet with longer length size. A larger packet also inhibits other devices from using the hub and it also requires larger memory size. Compare the packet delivery ratio values of both hub and switched networks. Explain why the packet delivery ratio values are different for two networks.
Switched networks have higher ratio of packet delivery than the hub networks.
Switched networks are intelligent, they can manage point to point packet delivery, this means no two computers can communicate concurrently, unlike in hub, where broadcasting is done blindly, which reduces packet delivery ratio.Calculate the Ethernet switched network theoretical packet delay value for 50 packets/sec?Total load
50*200*8*5+50*800*8*5=2 Mbits/sec.
Explain reasons why the switched network introduces higher end to end delay. Explain why the packet delay in a hub network increases with the load. Use the collision statistics to explain the hub network delay pattern Switched networks has to identify the address from the client, the retransmits the data to the client 1 only. The delay is brought about by the switch ethernet trying to established client 1 mac and compare to others.
Increase in load will need more time for packet delivery. More load also inhibits other devices from using the hub and it also requires larger memory size, this causes the delays.
5.0 Conclusion
Switched ethernet LAN can be used to minimize the number of collisions in the hub and thus increasing the quality of performances of hub networks. The results show that switched networks perform better than hub topology networks.
6.0 References
[1] Rahul Malhotra, Vikas Gupta, and Dr R. K. Bansal. “Simulation & Performance Analysis of Wired and Wireless Computer Networks” in Global Journal of Computer Science and Technology, Vol.11, Issue 3, March 2011.
[2] U. Black, Data communications and distributed networks. New Delhi, India: Prentice-Hall of India, 2008.
[3] P. Gonçalves, J. Oliveira and R. Aguiar, “A study of encoding overhead in network management protocols”, International Journal of Network Management, vol. 22, no. 6, pp. 435-450, 2012
[4] H. Singh, “Comparison of CSMA Based MAC Protocols of Wireless Sensor Networks”, International Journal on AdHoc Networking Systems, vol. 2, no. 2, pp. 11-20, 2012.
[5] Sameh H. Ghwanmeh, “Wireless network performance optimisation using Opnet Modeler,” Information
Technology Journal, vol.5, No 1, pp. 18-24, 2006.
[6]”Hub vs Switch – Difference and Comparison | Diffen”, Diffen.com, 2018. [Online]. Available: https://www.diffen.com/difference/Hub_vs_Switch. [Accessed: 21- Oct- 2018].
[7]”Ethernet Packet Rate and Throughput Calculations | Ciena Community”, Community.ciena.com, 2018. [Online]. Available: https://community.ciena.com/thread/1201-ethernet-packet-rate-and-throughput-calculations. [Accessed: 21- Oct- 2018].
[8] S. Alumur, B. Kara and O. Karasan, “Multimodal hub location and hub network design”, Omega, vol. 40, no. 6, pp. 927-939, 2012.
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