The sensor networks raise fundamental problems for the scientific community. These problems are due to the wireless communications, the density of nodes distribution, the resources constraints (energy, processor and memory), the low nodes reliability and the strongly distributed nature of the supported application. The specific particularities of the sensor networks make it difficult the guarantee of the real-time quality of service which remains currently an important challenge. This paper presents novel protocol solutions for sensor networks in hard real-time environments. We try to get the optimisation of both constraints at the same time: real-time communication delay guarantee and the energy consumption. Our routing and medium access strategy allows the load balancing, the interferences reduction and the real-time guarantee, for being based on a dynamic generation of real-time communication trees. The simulation results show that our routing and medium access protocols help the traffic load balancing to increase the system lifetime and the guarantee of real-time traffics.