An IP multicast broadcast device, an IP multicast receiver device, and a method of congestion control in reliable IP multicast are described that mitigate the impact of signal blockage in radio-based IP multicast networks. In one example multicast network, the IP multicast broadcast device, and the IP multicast receiver devices may be configured to support an IGMP-based multicast protocol in which a NORM protocol, a congested packet marking protocol, e.g., such as the ECN protocol described above, and a router congestion prediction protocol, e.g., such as the RED protocol, have been implemented. In addition, the implemented NORM protocol may implement a TCP congestion control algorithm that generates adjusted transmission rates based, at least in part, on a count of ECN congestion marked packets and a count of dropped packets at a selected receiver. As a result, the generated transmission rates are not unduly affected blockage of the radio-based transmission signal.