DEVS/NS-2 Environment: An Integrated Tool for Efficient Networks Modeling and Simulation

This paper presents a new DEVS/NS-2 modeling and simulation environment which supports both high and low levels of abstraction for network modeling and simulation. DEVS (Discrete Event System Specification) is a well-defined mathematical formalism specification for structure and behavior of dynamic systems. The NS-2 is a discrete event network simulator, whose primary use is intended to build and run various detailed network models and protocols such as TCP/IP, satellite links, and wireless networks. By combining the two powerful modeling and simulation systems, the significant benefits attained by the interoperable simulation of DEVS and NS-2 are reduction of the cost, increased high and low level modeling power, and enhanced reusability. To integrate the systems seamlessly, two major challenges are addressed. The first challenge is to synchronize the different ways of handling event schedules by the two simulation systems. This paper illustrates how the simulation time advances of DEVS and NS-2 are synchronized with each other. The latter problem is related to assigning the appropriate level of model structure and behavior within the combined system. The details of low level network with protocol and component description is modeled by NS-2 while DEVS serves as controller by modeling the high level behavior (e.g. use case scenario builder) of target network models and interaction of the associated actors. In this paper, we take two examples of wireless sensor networks. The first example is to describe our approach to the development process for modeling and simulation in DEVS/NS-2 environment, and the purpose of the second example is to show how DEVS/NS-2 environment is efficient for military system applications. This example is extended to demonstrate an effective way to make a decision on the appropriate level of sensor node's behavior. This leads to the discussion of tradeoffs between energy efficiency and effectiveness of decision making for the sensor network. The advantages and the disadvantages are discussed in the last part of this paper by comparing DEVS/NS-2 environment with its related studies such as DEVS BUS and OPNET.