Abstract: In some industry environments，there are one or more periodic real-time systems for monitoring and/or controlling purposes.Today，the attraction and penetration of the Internet are difficult to be kept out in these environments.It is worthy to study the topic of getting the best-effort services from the Internet while guaranteeing real-time traffics in a single system.Based on this，an IaI（Industry and Internet） switch is introduced and its queue scheduling is discussed in this paper.On the premise that three real-time and one best-effort queues exist in an IaI switch，four models of queues are analysed and the formulas for evaluating the maximum waiting time of real-time packets are given out.