Provided are method and apparatus for transmitting session-related parameters required for controlling session maintenance to a multicast agent in a relayed multicast network. The session manager in the relayed multicast network generates control data containing at least one of a T_PPROBE field, an N_PPROBE field, a T_HB field, a N_HB field, a T_HSOLICIT field, an N_HSOLICIT field, a T_HANNOUNCE field, a N_HANNOUNCE field, a T_RELAY field, an N_RELAY field, and a T_LEAVE field, and transmits the generated control data to the multicast agent. Accordingly, relayed multicast service can be provided for each session by setting session-related parameters for each session in a relayed multicast network and transmitting them to a multicast agent.