Internet Domain: TCP, UDP, SSL, and TLS
PHP type comparison tables
List of Supported Socket Transports
PHP Manual

## Unix Domain: Unix and UDG

unix:// and udg:// (udg:// since PHP 5).

- unix:///tmp/mysock
- udg:///tmp/mysock

unix:// provides access to a socket stream connection in the Unix domain. udg:// provides an alternate transport to a Unix domain socket using the user datagram protocol.

Unix domain sockets, unlike Internet domain sockets, do not expect a port number. In the case of fsockopen() the `portno` parameter should be set to 0.

Internet Domain: TCP, UDP, SSL, and TLS
PHP type comparison tables
List of Supported Socket Transports
PHP Manual