Performance Analysis of ALOHA and S-ALOHA Protocols

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MONASH UNIVERSITY
FACULTY OF ENGINEERING
ELEC3500 TELECOMMUNICATIONS NETWORKS
PERFORMANCE ANALYSIS OF ALOHA AND S-ALOHA PROTOCOLS
STUDENT’S NAME:
REGISTRATION NUMBER:
DATE:

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2. Summary
ALOHA and S-ALOHA protocols forms the basis of the random-access methods mostly used in
communication networks. This is due to their ease of applicability and simplicity nature. In this
lab, a complete model simulation of both ALOHA and S-ALOHA protocols were simulated and
explained step-by-step. The experimental work was developed based on the ALOHA model
developed for the OMNET++ package. There was no need to rebuild a new model since it was
already developed prior to the lab.
The aim of the experiment was to understand the techniques used in communication networks by
analyzing the performance of the ALOHA and S-ALOHA protocols under different loading
conditions. The simulation parameters were appropriately modified to obtain the desired
simulation results of the three sets of simulations.
The simulation results obtained were almost similar to the calculated theoretical results. It
indicted that the slots present in S-ALOHA are capable of increasing the normalized throughput
and efficiency of the system. It also reduces collision at the receiver end.
Table of Contents

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2. Summary......................................................................................................................................2
4. Introduction..................................................................................................................................2
5. Experiment...................................................................................................................................3
5.1. Objectives..............................................................................................................................3
5.2. Experimental description......................................................................................................3
5.3. Results and analysis..............................................................................................................5
5.4. Questions...............................................................................................................................9
6. Conclusion.................................................................................................................................11
References......................................................................................................................................12
Appendix........................................................................................................................................13
4. Introduction
The use of ALOHA and S-ALOHA protocols in communication networks has significantly
increased recently [6]. ALOHA is a simple computer networking system initially developed in

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the University of Hawaii hence its name (Additive Links On-line Hawaii Area). It was designed
to provide public wireless data packet [1]. Its terminals transmit the received packages without
delay [8]. It uses simple error detection code to detect errors at the receiver side. In case of an
error occurrence or collision at the receiver side, the packages are retransmitted again [2].
Therefore, it cannot utilize 100 percent of the communication channel capacity [3].
ALOHA exists in two main different versions, that is, pure ALOHA and slotted ALOHA [7]. In
pure ALOHA, whenever there is data in a station, it gets transmitted to the receiver. However, in
case more than one station transmit data packages simultaneously, a collision occurs which
damages the frame. In case of a destruction, the station has to wait for a random amount of time
so as to resend the data. Owing to the efficiency limitations of the pure ALOHA, slotted ALOHA
was devised [4]. The time in the shared channels are divided into equal slots thus minimizing the
possibility of collision. It allows the stations to send only one frame at the onset of the slot [5].
In this experiment, the performance analysis of ALOHA and S-ALOHA protocols used in
communication networks are investigated.
5. Experiment
5.1. Objectives
1. To understand the basic concepts of the random-access techniques used in
communication networks.
2. To understand the principles of ALOHA and S-ALOHA protocols.
3. To analyze the performance of ALOHA and S-ALOHA protocols for different load
conditions.
5.2. Experimental description
The lab experiment was developed based on the ALOHA model developed for the OMNET++
package. The simulation parameters were modified as given in the manual to obtain the required
results. Three sets of simulations ere run to obtain the desired experimental results.
In the case of SIMULATION 1, a pure ALOHA simulation model was used to determine the
normalized load vs throughput (S-G graph). After fixing packet size, the packet arrival rate per
host was calculated using the normalized load values. The load value was obtained by dividing
the total arrival rate by the system capacity.