Description
ELEC3500: OMNET++: Laboratory 2: Queuing Systems
Experiment: Characterisation of M/D/1, M/M/1 and M/M/1/K Queuing Systems in a Packet
Switched Network.
Required Reading Materials:
1. Recommend reading book pages 841-847 (2nd edition), Littleβs Formula and Basic Queuing
Models.
2. Lecture slides: Lecture_6-7.
Objective: In this simulation experiment, the behaviour of M/D/1, M/M/1 and M/M/1/K queuing
systems will be studied for different input traffic load and traffic patterns. The laboratory will also
examine the effect of buffer size selection on the traffic throughput in an M/M/1/K queue model.
Procedure:
This laboratory is designed based on queuing lectures and the FIFO model located in the ELEC3500
folder of the OMNET++ simulator. The simulation model is configurable from the omnetpp.ini file.
No model development is necessary for this laboratory – you only need to change simulation
parameters to obtain different results. To select appropriate simulation parameters you need to
calculate several basic simulation parameters. Use equations (1)-(3) below to calculate your
simulation parameters. First, you run the simulation model to obtain the delay and the queue length
data for all three queuing models. Following the first set of simulation, you need to run the model
with different parameters to obtain several simulation results with different random number seed
values to examine the effect of traffic variability. Random seed values are used in discrete event
simulations to represent different traffic and network operating conditions. Lastly, you need to
examine the effect of buffer size of a packet switch on the network traffic QoS (Quality of Service).
QoS of a traffic source is usually expressed in terms of packet delay and loss.
πΏπππ π = π/π (1)
ππππ£πππ π‘πππ π = 1/π (2)
πΌππ‘πππππππ£ππ π‘πππ π‘_πππ‘ = 1/π (3)
For all simulation models, run the simulation for 600 sec (i.e., 10 minutes) to collect data for analysis.
Use the service rate of 10,000 bits/sec and the packet size of 1000 bits. You need to collect and save
simulation results for writing your lab reports.
ELEC3500: OMNET++: Laboratory 2: Queuing Systems
M/D/1 Queuing System
First, you will use the simulation model to analyse the performance of an M/D/1 system which is
characterised by the exponential interarrival time of packets, with deterministic service time and a
single server. You can modify the omnetpp.ini file to configure the model to an M/D/1 system. You
need to collect the following results for the offered load values ο² = 0.1, 0.3, 0.5. 0.7, 0.9 and 1. To
simulate these load values, calculate the packet interarrival time.
Results to collect: Mean packet delay, mean queue length and mean queue delay. You can collect
these values from scalar files. You can export scalar and vector files to an Excel spreadsheet to further
process your results. You also need to collect the end-to-end delay and queue length plots for ο² = 0.3
and 0.9 (use the vector files).
M/M/1 Queuing System
Configure the simulation model for an M/M/1 system by changing the omnetpp.ini file. Use the
exponential distribution to represent the packet size. Collect results similar to those for the M/D/1
queue system. Also, collect similar vector files.
M/M/1/10 System
Configure the simulation model for an M/M/1/10 system by selecting the queue size to 10 packets.
Modify the omnetpp.ini file to convert your model from an infinite queue model to a finite queue
model. Collect results (scalar and vector) similar to those of the previous experiment. Using this
model, collect the packet loss statistics as well as the time-vs-packet-loss plots for ο² = 0.7 and 0.9.
Study the effect of queue size on traffic QoS:
For ο² = 0.95, increase the value of K in steps of 5 to obtain the packet loss of less than 15 packets.
Collect the packet loss and end-to-end delay for all values of K that you have used to obtain the packet
loss of less than 15 packets. Present these values in a table in your report.
Study effect of random number:
Use the M/M/1 model, set ο² = 0.6, collect the queue length plot using vector files. In this section, you
will compare the results generated by using the default seed value of the random number generator
and by using two other seed values. You can select any two seed values between 0 and 99, and run
the simulation model with these two seed values to collect the packet delay plots. Note down your
selected random number generator in the common section of the report as mentioned below.
Report Submission Instruction:
You need to submit a report with a common section and individual sections, preferably submitted
together. This section will be marked out of 40.
The common section should contain the following sub-sections:
β’ Introduction to the experiment, a single paragraph (200 words maximum) explaining the
objectives of the simulation laboratory.
ELEC3500: OMNET++: Laboratory 2: Queuing Systems
β’ Basic description of the simulation model used in the experiment (300 words maximum, 2
figures).
β’ Results: Provide following plots:
β’ It is suggested that you use five figures and one table in the following format:
1. Figure 1: Load versus M/D/1, M/M/1 and M/M/1/10 mean packet delays.
2. Figure 2: For the above queue systems: Load versus mean queue lengths.
3. Figure 3: For the above queue systems: Load versus mean queue delays.
4. Figure 4: M/M/1/10: Packet loss plots for the load values of 0.7 and 0.9.
5. Table 1: For ο²=0.95, Queue size vs packet loss.
6. Figure 5: M/M/1 packet delay for three different random numbers.
β’ Analysis: Briefly analyse the delay-vs-load graphs obtained for all three queue models to
differentiate the performance of these models.
Individual section: Answer the following questions. The answers are to be provided by each group
member separately.
1. Calculate the theoretical end-to-end delay values for M/M/1/10 and M/M/1 models, using ο² =
0.5 and 0.7. Use the same service rate as that in the simulation model.
[10]
2. Compare the theoretical values calculated in Question 1 with the simulation results obtained.
Explain why these results are the same or different? To answer this question, you also use
information from your vector plots.
[10]
3. Compare the delay and packet loss values obtained using the M/M/1 and M/D/1 models. Explain
the differences you can observe by examining the load vs delay and packet loss plots.
[10]
4. Explain the effect of using a random number for different seed values in the simulation model.
Do you see any change of the packet delay distribution? Explain any differences you have
observed using the different seed values.
[10]
5. Explain the effect(s) of buffer size selection on the QoS value of the outgoing traffic of a network
switch.
[10]
6. Consider a real communication network where you donβt have control over the traffic arrival
process. What changes can you make within a packet switched node to reduce the probability of
packet losses and high end-to-end delay?
[10]
Report submission date:
The lab report is due on Friday at 11.59pm of the following week after the lab is performed. Submit
your report via the Assessment tab of the blackboard. One of the group memberβs submission should
have the common section. Write the group members name on both reports. Please include the
university assessment cover sheet with your submission.
