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

 s
    A socket descriptor created with the socket() function.
 msg
    A pointer to a buffer containing the data to be sent.
 len
    The length of the data pointed to by the msg argument.
 flags
    Can be either 0 or MSG_OOB. If it is MSG_OOB, the data is sent
    out of band. Data can be received before other pending data on
    the receiving socket if the receiver specifies MSG_OOB in its
    flag argument of its recv(), recvfrom()  or recvmsg() call.
 to
    Points to the address structure of the socket to which the data
    is to be sent.
 tolen
    The length of the address pointed to by the to argument.