This Recommendation specifies the functional requirements of interactive low-latency multimedia transmission system (ILMTS) over the Internet. It identifies the key functional requirements from the different aspects, such as service level, application level and management level, etc. According to those requirements, this Recommendation also introduces a reference framework of ILMTS. Some use cases are described in the Appendix at the end of this Recommendation. With this Recommendation, the service providers who provide the interactive live content delivery service with low-latency media delivery are able to design a standardized real-time multimedia service system by following the requirements defined in this Recommendation.