IP Multicasting for Receiving Streams

Hi Friends,

In RL-ARM documentation it gives an example about multicasting as in follows;

U8 sgroup[4] = { 238, 0, 100, 1}; ..
if (igmp_join (sgroup) == __TRUE) { printf ("This Host is a member of group: %d.%d.%d.%d\n", sgroup[0],sgroup[1],sgroup[2],sgroup[3]);
}

..

However, stream in server side we define a multicast ip group and port number, such as if we use vlc player in linux environment;

vlc -vvv file.ogg –sout udp:239.0.0.1:1234 –ttl 12 –loop

In embedded system using RL_ARM how could I establish this? Do I have to open UDP port first, and join this ip group? That is;

udp_soc = udp_get_socket (0, UDP_OPT_SEND_CS | UDP_OPT_CHK_CS, udp_callback);
udp_open (udp_soc, 0);

...

igmp_join ("239.0.0.1"); // Why this api has no port number parameter????

Waiting help from experts.
Best Regards