Patent ID: 7751395

Claim:
A method for preventing simultaneous issuance of two multicast flows, comprising: ceasing, by a digital subscriber line access multiplexer (DSLAM), a transmission of a multicast flow to an Internet protocol set-top box (IP STB) when the IP STB is switched on; automatically composing and sending an IGMP Report message, by the IP STB immediately upon being switched on, based on contents of a channel list stored in the IP STB, and joining a multicast group of a default switch-on channel; according to a received user instruction, performing switching channels, wherein the switching channels comprises: sending the IGMP Leave message to leave a current multicast group; searching a multicast IP address and a multicast port number of a channel chosen by a user in a channel list; composing the IGMP Report message based on the multicast IP address and the multicast port number found and sending the IGMP Report message to join a new multicast group; when the IP STB joining the new multicast group, if the channel chosen by the user is not the default switch-on channel, updating the multicast IP address, the multicast port number and verification information of the new multicast group with the multicast IP address, the multicast port number and verification information stored in the IP STB; and if the channel chosen by the user is the default switch-on channel, not updating the multicast IP address, the multicast port number and verification information of the new multicast group.