VMS Help TCPIP Services, Programming Interfaces, Sockets API, socket(), Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 af
    The address family used in later references to the socket.
    Addresses specified in subsequent operations using the socket
    are interpreted according to this family. Currently, only the AF_
    INET (internet) and TCPIP$C_AUXS addresses are supported.
    For a network application server with the LISTEN flag enabled,
    you specify the TCPIP$C_AUXS address family to obtain the
    connected device socket created by the auxiliary server in
    response to incoming network traffic. For an example of this
    situation, refer to the example in <REFERENCE>(EX_TCP_ASRV_SOCK).
 type
    The socket types are:
    o  SOCK_STREAM - Provides sequenced, reliable, two-way,
       connection-based byte streams with an available out-of-band
       data transmission mechanism.
    o  SOCK_DGRAM - Supports datagrams (connectionless, unreliable
       data transmission mechanism).
    o  SOCK_RAW - Provides access to internal network interfaces.
       Available only to users with either a system UIC or the SYSPRV
       privilege.
 protocol
    The protocol to be used with the socket. Normally, only a single
    protocol exists to support a particular socket type using a given
    address format. However, if many protocols exist, a particular
    protocol must be specified with this argument. Use the protocol
    number that is specific to the communication domain in which
    communication takes place.