Abstract: - This paper presents a comparative study of two well-known network simulators: OPNET Modeler and Ns- 2. Other studies in this area have generally been confined to just one simulator. The motivation of this paper is to provide a guide to researchers undertaking packet-level network simulations. The simulator outputs were compared to the output from a live network testbed. The experimental comparison consisted of deploying both CBR data traffic, and an FTP session, both on the network testbed and the simulators. CBR data traffic was used due to its simplicity of modeling. A custom analysis tool was employed to examine the behavior of the network in different background traffic scenarios. The same scenarios were then recreated in the simulators in order to ascertain their realism. The results show the necessity of fine-tuning the parameters within a simulator so that it closely tracks the behavior of a real network.
Keywords: network simulator, OPNET Modeler, Ns-2, simulation methodology
1 Introduction
Network simulators have grown in maturity since they first appeared as performance, management and prediction tools. Simulators are normally used as network management tools, for which packet level analysis is not commonly employed. However, more studies are needed to establish guidelines for researchers so that they may select and customise a simulator to suite fine-grained packet level analysis [1][2]. Reference [3] reports `the breach of credibility' that studies based on simulation tools need to tackle; one motivation behind this paper is to address this need. The ease and facility that simulators provide in evaluating “radical” changes to a network environment cannot be discarded. There are a considerable number of simulations tools in the market. The main characteristics that divide them are: accuracy, speed, ease of use, and monetary expense.
This paper concentrates on the accuracy of the simulation in comparison to a real network for packet level analysis. Two of the currently popular network simulators that can perform this type of analysis are Modeler from OPNET1 [4] and Ns-2 from the Virtual Internetwork Testbed project VINT [5]. These are selected because of their popularity within academia, commercial and industrial communities [6].
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Gilberto Flores Lucio, Marcos Paredes-Farrera, Emmanuel Jammeh, Martin Fleury, Martin J. Reed Electronic Systems Engineering Department University of Essex Colchester, Essex C04 3SQ United Kingdom
gflore@essex.ac.uk, http://privatewww.essex.ac.uk/~gflore/
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