Industrial networks are typically used to monitor safety-related processes where high reliability and an upper bounded latency are crucial. Because of its flexibility, wireless is more and more popular, even for real-time applications. Because radio transmissions are known to be lossy, deterministic protocols have been proposed, to schedule carefully the transmissions to avoid collisions. In parallel, industrial environments now integrate mobile industrial robots to enable the Industry 4.0. Thus, the challenge consists in handling a set of mobile devices inside a static wireless network infrastructure. A mobile robot has to join the network before being able to communicate. Here, we analyze this attachment delay, comprising both the synchronization, and the negotiation of dedicated cells. In particular, since the control frames (EB and 6P) have a strong impact on the convergence, our proposed model carefully integrates the collision probability of these packets. We validate the accuracy of our model, and we analyze the impact of the different EB transmission policies on the discovery delay. Our performance evaluation demonstrates the interest of using efficiently the radio resources for beacons to handle these mobiles devices.