The number of battery-operated devices with wireless communication capabilities has increased enormously in the last years and is expected to increase even more in the future. A fundamental need in these systems is to guarantee a minimum system lifetime and timing constraints through a careful management of energy, communication, and computational resources. This paper describes WBuST, a MAC layer protocol designed to bound the maximum delay of real-time messages and guarantee the system lifetime by properly allocating a share of the available bandwidth to each node of the network. The protocol allows multi-hop wireless communication under different network topologies. The proposed approach is assessed through theoretical analysis and experimental results.