Abstract: The HLA-RTI provides a general-purpose network communication mechanism for Distributed Interactive Simulation (DIS), but it has limitations on Real-Time DIS (RT-DIS). The Internet is moving to an age of QoS, providing delay and jitter bounded services. With IP QoS and a real-time operating system, HLA makes it possible to construct a real-time architecture for RT-DIS, a critical aspect of applications in virtual medicine, distributed virtual environments, weapon simulation, aerospace simulation, and others. This paper outlines the current real-time technology at the operating system and network infrastructure level. It then summarizes the requirements and the experience of using RT-DIS. After analyzing the limitations of current HLA and RTI, a proposal of a real-time extension to HLA is presented and an architecture for real-time RTI is suggested. Similar to the growth of real-time CORBA after the mature based CORBA standard suite, Real-Time HLA is a natural extension following the standardization of HLA as IEEE 1516 in September of 2000.