// Create the UDP channel on which all communication will take place.
// The channel is created on the default network interface and reserves the chat port for use.
errChk (CreateUDPChannel(PORT, &gUDPChannel));
// Assign a callback function to be notified when data arrives on the channel.
errChk (SetUDPAttribute(gUDPChannel, ATTR_UDP_CALLBACK, UDPChatCallback));