This article addresses the problem of data delivery probability estimation for RTPS (real-time publish-subscribe), built on the top of the UDP/IP protocol using Ethernet. Ethernet in general is not deterministic due to its media access control (CSMA/CD) and its behaviour under transient overload is not sufficient for any real-time application. On the other hand, when the applications have predictable and bounded number of requests, behaviour of Ethernet is "nearly" real-time (very low probability of delayed data delivery). Ethernet is very attractive for the automation area due to its availability and low implementation cost. This article uses a simulation approach since it offers more flexibility, especially for large networks. The simulation results are compared to analytical ones.