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

 d
    A descriptor that must refer to a socket or file currently opened
    for reading.
 buffer
    The address of a user-provided buffer in which the input data is
    placed.
 nbytes
    The maximum number of bytes allowed in the read operation.