ELEC3500-Lab4 Simulation Experiment IV Solved

This laboratory has been developed based on the ALOHA model of the OMNET++ package. Find the model under the ELEC3500 folder of the OMNET++ directory. The model has been prebuilt so you don’t need to develop or change any code in the model. Make sure that you use the ALOHA project in the ELEC3500 folder. You need to modify simulation parameters in the omnetpp.ini file to obtain necessary simulation results. Use simulation parameters listed in table-1 to obtain necessary simulation results. Check the .ini file and change parameters appropriately.

Table: 1- Simulation parameters 

Simulation Parameter 
Value(s) 
Simulation length (sime-time-limit) 
900s 
No. of hosts 
12 
Aloha.host[*].radioDelay 
0ms 
Packet length 
1728 bits 
Packet size distribution  
Constant, exponential (only for second 

ALOHA simulation) 
Transmission rate 
19200 bits/sec 
S-ALOHA slot time  
100 ms 
Total offered load (normalised) 
For both ALOHA and S-ALOHA: 

 0.1, 0.25, 0.4, 0.55, 0.7, 0.85, 1, 1.25, 1.5, 

1.75, 2 
Random number seed values 
Use the default value and a second value only for the second ALOHA simulation. 
You need to run three sets of simulations to obtain necessary results for the simulation experiment.

Simulation 1:  

In this experiment you will use the ALOHA simulation model to obtain the S-G graph (normalised load vs throughput). In the first simulation you will use a fixed packet size. Calculate the packet arrival rate per hosts using the normalised load values. The normalised load value is obtained by dividing the total arrival rate by the capacity of the system.

Example: Assume an ALOHA system uses transmission rate of 100 kbits/sec and 2000 bits packet size. Calculate the arrival rate in packets/sec at a normalised load of 0.2. Also, calculate the corresponding packet interarrival time of each host, assuming the network has 5 hosts.

                                           𝑅𝑅        100×103

 System capacity 𝐶𝐶 =   =                 = 50 packets/sec

                                           𝐿𝐿            2000

Total arrival rate at 0.2 normalised load 𝜆𝜆 = 50 × 0.2 = 10 packets/sec

Number of packets/ host 𝜆𝜆𝐻𝐻 = 105 = 2 packets/sec

1

Packet interarrival time 𝑇𝑇𝑖𝑖𝑖𝑖𝑖𝑖 =  𝜆𝜆𝐻𝐻 = 0.5 𝑠𝑠𝑠𝑠𝑠𝑠 

In this simulation obtain three scalar data values which will be used to generate performance plots/table.

Scalar values to collect: Channel utilisation, number of received frames and number of collided frames. Note that channel utilisation statistics of the simulation model represents the normalised throughput. Normalised load vs the channel utilisation represents the S-G graph of a MAC protocol.

Collect these values for all simulation normalised loads from 0.1 to 2.

Simulation 2: 

In this experiment you will use the ALOHA model to obtain same results as in simulation 1. In this model change the packet length distribution using the exponential distribution, use the same packet size value as the mean value of the exponential distribution function. You need to obtain two set of results using two different random number values. Use the default random number seed value as used in simulation 1 and two different seed values. In this simulation collect the same statistics as simulation 1.

Simulation 3: 

In this experiment you will use the S-ALOHA simulation model. For this simulation, use the same parameters as simulation 1 (i.e. use the same fixed size packet). Obtain the same simulation results as simulation 1. Note that you will change the inter-arrival time value under the S-ALOHA code section in the ini file.