Hi Daniel,
From the RTCS user's guide I can see that you will need to join a multicast group. Here is the example from the user's guide:
uint_32 sock;
struct ip_mreq group;
group.imr_multiaddr = multicast_ip_address;
group.imr_interface = local_ip_address;
error = setsockopt(sock, SOL_IGMP, RTCS_SO_IGMP_ADD_MEMBERSHIP, &group, sizeof(group));
I hope this helps.
Regards,
-Garabo