Socket Domains

## 21.1 Socket Domains

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 the 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.