Each member of a group has a unique address. In JChannel, it is the IP address of the machine on which the stack is running and the port on which the stack is receiving incoming messages; it is represented by class JavaGroups.JavaStack.Address. Instances of this class are only used within the JChannel protocol stack; users of a channel see addresses (of any kind) only as objects (opaque). Since an address uniquely identifies a channel, and therefore a group member, it can be used to send messages to that group member.