Currently there are two available domains, unix and internet. The communication in the unix domain is limited to a single machine running under an Unix operating system, and the sockets are associated to files in this machine’s file system.
The internet domain can be used to connect any two machines which are connected through the network. It can also connect two processes on the same machine. The address of a socket is then identified by the host name and the port number. The host name is the same as obtained, e.g., with get_flag(hostname, Host). The port identifies the channel on the host which is used for the communication. This is available under both Unix and Windows operating systems.