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

 s
    A socket descriptor that is in a connected state as a result of a
    previous call to either connect() or accept().
 how
    How the socket is to be shut down. Use one of the following
    values:
    0     Do not allow further calls to recv()  on the socket.
    1     Do not allow further calls to send()  on the socket.
    2     Do not allow further calls to both send()  and recv().