Network Simulation via Hybrid System Modeling: A Time-Stepped Approach

The ever increasing complexity of networks dramatically increases the challenges faced by service providers to analyze network behavior and (re)provision resources to support multiple complex distributed applications. Accurate and scalable simulation tools are pivotal to this cause. Currently, network modeling and simulation tools are based either on packet-based discrete event models or fluid models. Both are limited in that the performance of discrete event based simulators does not scale to large networks while fluid models cannot accurately capture the behavior of all phases of a network's dynamics. The recently proposed hybrid systems model for data communication networks shows promise in achieving performance characteristics comparable to fluid models while retaining the accuracy of discrete models. Using the hybrid systems paradigm, this paper provides contributions to the modeling of TCP behavior and the analysis/simulation of data communication networks based on these models. An important distinguishing feature of our simulation framework is a faithful accounting of link propagation delays which has been ignored in previous work for the sake of simplicity. Other salient aspects of our work include a new finite state machine model for a drop-tail queue, a new model for fast recovery/fast retransmit mode, a revised sending rate model, and an embedded time-out mode transition mechanism all of which employ a time-stepped solution method to solve the hybrid system network models. Our simulation results are consistent with well-known packet based simulators such as NS-2, thus demonstrating the accuracy of our hybrid model. Our future efforts will be directed towards studying and improving the computational performance of hybrid model based simulations.