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

    You can use this function only on connected sockets. To send
    data on an unconnected socket, use the sendmsg() or sendto()
    function. The send() function passes data along to its connected
    peer, which can receive the data by using the recv() or read()
    function.
    If there is no space available to buffer the data being sent
    on the receiving end of the connection, send() normally blocks
    until buffer space becomes available. If the socket is defined as
    nonblocking, however, send() fails with an errno indication of
    EWOULDBLOCK. If the message is too large to be sent in one piece,
    and the socket type requires that messages be sent atomically
    (SOCK_DGRAM), send() fails with an errno indication of EMSGSIZE.
    No indication of failure to deliver is implicit in a send(). All
    errors (except EWOULDBLOCK) are detected locally. You can use the
    select() function to determine when it is possible to send more
    data.
    Related Functions
    See also read(), recv(),  recvmsg(), recvfrom(), getsockopt(),
    and socket().