There are strong interests of using cheap and simple Ethernet technology for industrial control networks. However, traditional Ethernet is shared network using CSMA/CD protocol, which cannot ensure data determination and real-time reliability. Given the measured total delay distribution, this paper analyses the types of real-time data transmitted in industrial control networks and illustrate a hypothetical probability density function to describe the total delay in data delivery. Finally, the point of paper is put forward on devising an efficient method to estimate the delay probability of flows, especially those with multiple competing