An address format indicates what set of rules was used in creating network addresses of a particular format. For example, in the Internet communication domain, a host address is a 32-bit value that is encoded using one of four rules based on the type of network on which the host resides. Each communication domain has different rules for valid socket names and interpretation of names. After a socket is created, it can be given a name according to the rules of the communication domain in which it was created. For example, in the UNIX communication domain, sockets are named with operating system path names.
Sockets normally exchange data only with sockets in the same communication domain.
The socket subroutine takes an address family as a parameter. Specifying an address family indicates to the system how to interpret supplied addresses. The NDD domain enables applications to run directly on top of physical networks. A socket name in the NDD domain consists of AIX NDD name and a second part that is protocol dependent. Communication domains are described by a domain data structure that is loadable.