This Recommendation specifies the requirements and the referenced architecture of the open IPTV multicast service. In this Recommendation, two solutions are introduced for different scenarios: a dedicated open IPTV multicast service system solution and an interface solution for exposing IPTV multicast network capability. The related functional components, requirements and the reference points are also defined accordingly. With this Recommendation, IPTV service providers are able to expose their dedicated multicast network capability to the third parties so that the OTT live broadcast service deployed on the public Internet could improve its QoE by taking advantage of the dedicated multicast network. Furthermore, new "live +" service may be developed based on the open multicast service defined in this Recommendation.