ns-2 vs. OPNET: a comparative study of the IEEE 802.11e technology on MANET environments P. Pablo Garrido, Manuel P. Malumbres Miguel Hernandez University Avda. Universidad, s/n - 03202 Elche, Spain {pgarrido,mels}@umh.es Carlos T. Calafate Technical University of Valencia Camino de Vera, s/n - 46022 Valencia, Spain calafate@disca.upv.es ABSTRACT In this work we present the results of a comparative study between two well-known network simulators: ns-2 and OP- NET Modeler. In particular, we focus on a performance evaluation of the IEEE 802.11e technology on Mobile Ad-hoc Networks (MANETs) in both stationary and mobile scenar- ios. The paper describes the tested scenarios in detail, and discusses simulation results obtained with OPNET Modeler, comparing them with those obtained with ns-2. The per- formance of IEEE 802.11e in the presence of legacy IEEE 802.11 stations is also analyzed. Due to the significant differ- ences between both simulators, we enumerate those changes required so as to make results obtained via both simulators comparable. The results that have been reached support the conclusion that the behavior of both simulators is quite similar in general. Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Wireless com- munication General Terms Algorithms, Measurement, Performance Keywords MANET, 802.11e, Network simulators, performance com- parative 1. INTRODUCTION A Mobile Ad-hoc Network (MANET) is composed by a group of stations that communicate wirelessly with each other to form a network without the need for any infras- tructure or centralized control. Two of the most important factors that characterize MANETs are the routing protocol and the wireless technology employed by the stations within the network. When referring to wireless technology we mean Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. SIMUTools , March 03 – 07, 2008, Marseille, France. Copyright 2008 ACM ISBN 978-963-9799-20-2 ...$5.00. the combination of the physical (PHY) and Medium Access Control (MAC) layers of the protocol stack. The IEEE 802.11 standard [1] was created to provide wire- less local area networks (WLANs) to different environments, such as public access networks, enterprise networks, or home networks. It operates in free bands such as the industrial, scientific and medical (ISM) band at 2.4 GHz or in the un- licensed 5 GHz band. The IEEE 802.11e [2] task group has finished some extensions to the IEEE 802.11 standard to provide Quality of Service (QoS) at the MAC level. The availability of a wireless technology that offers QoS support is one of the most important requirements to deploy a QoS framework in MANET environments. By enabling traffic differentiation at the MAC level it is possible to design a strategy, built on top of the IEEE 802.11e technology, that can successfully support traffic with QoS constraints. Exam- ples of QoS traffic include VoIP, videoconference, and that generated by any other real-time application. Supporting real-time video and voice traffic in MANETs is an upcoming need that results from the fusion of two techno- logical areas that have been receiving much interest in the past few years. On the one hand, the proliferation of de- vices with embedded audio/video capturing and processing capabilities has made audiovisual communications the new human communication paradigm. On the other hand, re- cent improvements in network technologies aim at support- ing mobile wireless communications through self-configuring and fully flexible networks. Therefore, one of the greatest technological challenges to be met, according to the current state-of-the-art, is providing real-time peer-to-peer video- conference systems in MANETs. To achieve this goal QoS support stands as an essential condition. Most published research works about MANETs use simu- lation tools [11], but the reliability of such simulation studies has been questioned [7, 17, 3]. Because of this, some com- parative studies have been conducted in order to validate the obtained results [12, 8]. This paper presents a compar- ative analysis of two well-known network simulators, ns-2 v2.26 [15] and OPNET Modeler v14.0 [16]. We focus on the accuracy in simulating IEEE 802.11e technology in MANET environments. For IEEE 802.11e evaluation in ns-2 we relied on the extensions from [20], while for OPNET we relied on the IEEE 802.11e model that is built-in. Results obtained with the ns-2 simulator have already been published in [5]. The motivation of this paper is to repeat all the experi- ments under the same conditions using OPNET, in order to validate the accuracy of both simulators for some particu- lar MANET scenarios. Similarly to that previous paper, all