The current project I am working uses RTX with TCPnet. The project uses TCP, UDP broadcast, unicast, and multicast. We bought and installed the RTL within the last 6 months. The multicast functions do not work! Here are some problems I have found: Domuntation: The udp_get_socket function is in the RL-TCPnet library. The prototype is defined in rtl.h. source http://www.keil.com/support/man/docs/rlarm/rlarm_udp_get_socket.htm The igmp_join function is in the RL-TCPnet library. The prototype is defined in rtl.h. source http://www.keil.com/support/man/docs/rlarm/rlarm_igmp_join.htm The igmp_leave function is in the RL-TCPnet library. The prototype is defined in rtl.h. source http://www.keil.com/support/man/docs/rlarm/rlarm_igmp_leave.htm None of these things are defined in the RTL.h file. Where are they, or do they exist? I am wating on KEIL to respond to my support request.