在java中的不同网络中进行多播

I'm writing a code to work through sockets in java. I've created a multicast group to which anybody can join on the LAN. But the LAN has many different networks, operated by a router, and the multicast group created by the code would be different in different network and if a person multicast's something to the multicast group in the network A it will only be received by the people joined to the group in that network only, and not by all the people's in different networks.I'm writing a code to work through sockets in j