all numeric zeros 5 a 60 the sin_family member of sock_addr is set to af_inet 5 b 00 the s_addr member of the sin_addr member of sock_addr is set to the ip multicast address of the destination multicast group 5 b 10 the sin_port member of sock_addr is set to the port number 5 b 20 the multicast transmission of data is attempted by invoking u201c sendto u201d and passing as parameters the integer status data and number of bytes in data a pointer to sock_addr and the number of bytes in sock_addr and setting the integer status to the return code of the call to sendto 5 b 30 if status is less than numeric 0 5 b 40 indicating failure on the sendto call the program is exited in an error condition 5 b 50 otherwise the program is exited in a success condition 5 b 60 fig6 a through 6b present detailed logic in a flow chart of a computer software program that receives ip multicast data using sockets in accordance with a preferred embodiment the receiver program on the multicast router is labeled 6 a 00 an ip address structure named u201c sock_addr u201d a data buffer named u201c data u201d a multicast request structure name u201c m_req u201d and an integer named u201c count u201d are instantiated 6 a 10 status is set to the return code of a call to u201c socket u201d.