UDP is meant to be at the bottom of a stack. It sends messages received from its upper layer using unreliable UDP and IP multicast, and passes up messages received from the network up to the next higher layer. When started, it opens a unicast and multicast socket: the unicast socket is used to send/receive unicast messages, whereas the multicast socket sends/receives multicast messages. The channel's address will be the address and port number of the unicast socket. UDP adds a header with the group name to each outgoing message and strips incoming messages off their header. If a header's group name does not match the channel's group name, it will be discarded (many channels can use the same IP multicast address, therefore the group name has to be used as discriminator).