The digital universe is growing at significant rates in recent years. One of the main responsible for this is the Internet of Things, or IoT, which requires a middleware that should be capable to handle this increase of data volume at real-time. The article aims at presenting an IoT performance evaluation model named IOTBENCH, which offers a framework to evaluate IOT systems on both centralized and distributed architectures when varying parameters such as requesting threads, number of tags and number of RFID readers. Particularly, we are focusing our evaluation over one of the most used middlewares to enable IoT worldwide named Fosstrak. The main idea is to observe the middleware scalability under different situations, showing in detail when a single computer is enough to handle IoT demand, and when it is not.