Modeling and simulation is one of the important tools in protocol research. By using simulation, protocol's peformance can be investigated with low cost. NS2 is a widely used network simulator in protocol research, which employs an informal modeling approach. Within the approach time and state information of models are not explicitly described, thus being hard to validate model.
The DEVS formalism is a mathematical framework for modeling a discrete event system in a hierarchical, modular manner. Basically, protocol is a kind of discrete event systems and the DEVS formalism is an ideal candidate for it. In DEVS, model's time and state information is described explicitly. By using DEVS formalism, models can easily be validated and errors in modeling stage can be reduced. However, the DEVS simulator, DEVSim++, supports a small amount of model library that are needed to build simulation models of network.
Although NS2 employs an informal modeling approach and models validation is difficult, it supports an aboundant of model library validated by experimental users. The model library of NS2 includes models of protocols, links and queuing disciplines. Thus, time to develop simulation model can be greatly reduced by reusing such a model library.
This thesis is proposed to develop protocol models in which some are DEVS models and others are NS2 models.
To Simulate DEVS models and NS2 models together requires an interoperation between DEVSim++ and NS2 simulators. The interoperation showed support the followings. First, models and simulators are compared, and then it is specified how to interoperate them. Secondly, it is specified how to synchronize simulation time and how to transfer data. Global virtual time(GVT) is used to synchronize simulation time; Shared memory is used to transfer data between DEVSim++ and NS2. To implement an interoperation environment two modules are defined: adapter and interoperation coordinator. Adapter is implemented in each simulator, which controls each simulator and provides abstracted view to interoperation coordinator. Interoperation coordinator controls each adapter so that all events in an overall model are in a causal order.
Correctness and effectiveness of the implemented interoperation environment have been shown by simulation of UDP and TCP-Reno models. We exchanged some NS2 models with the corresponding of DEVSim++ ones, then experimented on the mixed simulation models in interoperating environment. We confirmed that I/O traces of NS2 models are equivalent to those of a mix of NS2 and DEVSim++ models.
We evaluated the performance of the interoperating environment. It was shown that the performance degradation of the interoperating environment compared with the NS2 simulator was moderate.
