Stochastic discrete event simulation methodology is becoming increasingly popular among network researchers worldwide in recent years. This popularity results from the availability of various sophisticated and powerful simulation software packages, and also because of the flexibility in model construction and validation offered by simulation. In this chapter, the authors describe their experience in using the network simulator 2 (ns-2), a discrete event simulation package, as an aid to modeling and simulation of the IEEE 802.11 Wireless Local Area Networks (WLANs). This chapter provides an overview of ns-2 focusing on simulation environment, architecture, model development and parameter setting, model validation, output data collection and processing, and simulation execution. The strengths and weaknesses of ns-2 are discussed. This chapter also emphasizes that selecting a good simulator is crucial in modeling and performance analysis of wireless networks.
TopIntroduction
The use of discrete event simulation packages as an aid to modeling and performance evaluation of WLANs has grown in recent years (Bianchi, 2000; Chen, Jian, & Lo, 2002; Das, Castaneda, & Yan, 2000; Fantacci, Pecorella, & Habib, 2004; Tickoo & Sikdar, 2003). This popularity is due to the availability of sophisticated simulation software packages and low cost powerful personal computers (PCs), but also because of the flexibility in rapid model construction and validation offered by simulation.
A detailed discussion of simulation methodology, in general, can be found in numerous literature (Carson, 2004; Law & Kelton, 2000). More specifically, Pawlikowski (1990) in a comprehensive survey of problems and solutions suited for steady-state simulation highlighted the relevance of simulation technique for modeling and performance evaluation of telecommunication networks. This view of simulation and modeling is frequently supported in the wireless communication and networking literature (Hassan & Jain, 2004; Holloway, 2003; Nicopolitidis, Obaidat, Papadimitriou, & Pomportsis, 2003; Sarkar & Pawlikowski, 2002).
A typical WLAN can easily be simulated and its performance evaluated by a network software package (i.e., simulator). It is important for researchers to choose a simulator which is easy to use; more flexible in model development, modification and validation; and incorporates appropriate analysis of simulation output data, pseudo-random number generators, and statistical accuracy of the simulation results (i.e., desired relative precision of errors and confidence interval). These aspects of credible simulation studies are recommended by leading network simulation researchers (Law & Kelton, 2000; Pawlikowski, Jeong, & Lee, 2002; Schmeiser, 2004).
While various simulators exist for building a variety of WLAN models, we briefly describe two popular network simulators namely, ns-2 (Fall & Varadhan, 2011) and OPNET Modeler (www.opnet.com). The ns-2 simulator is one of the most commonly used simulators today and is very popular with researchers, including CS and EE students worldwide. The ns-2 is open-source software and provides an environment for rapid model construction and simulation output data collection.
OPNET, developed by OPNET technologies, is another popular commercial software package commonly used by researchers and practitioners for modeling and performance evaluation of telecommunication networks. It has a robust and flexible wireless node model which consists of process models of the different layers of the network protocol stack. As ns-2, OPNET is an object-oriented simulation package. However, unlike ns-2, it is totally menu-driven with an easy-to-use Graphical User Interface (GUI) for rapid model construction, data collection and other simulation tasks. It is often of interest to study a proposed or existing wireless network to gain insight into its expected behavior. However, since experimentation with the live network is disruptive and not very cost effective, a model is required for this purpose.
This chapter emphasizes that selecting a good network simulator is crucial in modeling and performance analysis of wireless communication networks. Both the ns-2 and OPNET offer flexibility in model construction and validation, and incorporates appropriate analysis of simulation output data, pseudo-random number generators, and statistical accuracy of the simulation results. Without an underlying framework for the model, a valid, verifiable model become much more difficult to develop, particularly in the time-constrained environments found in many wireless application areas.
The remainder of this chapter is organized as follows. We first provide an overview of ns-2 simulator and then describe our experiences in using ns-2 as an aid to modeling and performance evaluation of IEEE 802.11 WLANs. The strengths and weaknesses of ns-2 are discussed, and a brief conclusion ends the chapter.