Currently, wireless sensor networks (WSNs) are not used in application scenarios that require timely reaction to sensor data for two main reasons. First, there is no exact method to dimension a wireless sensor network before deployment such that both delay and reliability are guaranteed. Second, most existing network components aim to be energy efficient while a few aim to minimize delay. However, none have considered a deterministic performance regarding both delay and reliability. Given the required message transfer delay D and reliability R, our proposed framework can dimension and then operate a WSN to satisfy these requirements.