Abstract -Nowadays, systems based on Wireless Sensor Networks are intensively used in various fields. However, there are few real time applications employing WSNs. The problem resides in various limitations especially at the level of their communication capabilities. Various researches were conducted in this direction but theoretical models are still far from physical reality. The work presented in this paper aims to identify some hard-to-be-modeled aspects using practical measurements on a real time WSN. Experiments were conducted on a network using IEEE 802.15.4 compliant communication modules, including the widespread ZigBee solution.