The network pseudodevice allows physical, logical, and virtual
    I/O functions. The physical and logical I/O functions are used
    only with the IP layer. See the following table for a list of the
    basic I/O functions and their modifiers. The sections that follow
    describe in greater detail the operation of these I/O functions.
    The following table describes the network pseudodevice driver I/O
    functions.
    Function Code and    Function
    Arguments            Modifier        Description
    IO$_ACCESS p3,p4     IO$M_ACCEPT     Opens a connection.
                         IO$M_EXTEND
                         IO$M_NOW
    IO$_ACPCONTROL p1,                   Performs an ACP (ancillary
    p2, p3, p4                           control process) operation.
    IO$_DEACCESS p4      IO$M_NOW        Aborts or closes a
                         IO$M_SHUTDOWN   connection.
    IO$_READVBLK         IO$M_EXTEND     Reads a virtual block.
    p1,p2,p3,p4,p6       IO$M_
                         INTERRUPT
                         IO$M_LOCKBUF    Controls the buffer
                         IO$M_PURGE      operations.
    IO$_SENSEMODE                        Reads the network
    p2,p3,p4,p6                          pseudodevice
                                         characteristics.
    IO$_SENSECHAR                        Reads the network
    p2,p3,p4,p6                          pseudodevice
                                         characteristics.
    IO$_SETMODE p1,p2,   IO$M_OUTBAND    Sets the network
    p3,p4,p5             IO$M_READATTN   pseudodevice characteristics
                         IO$M_WRTATTN    for subsequent operations.
    IO$_SETCHAR p1,p2,   IO$M_OUTBAND    Sets the network
    p3,p4,p5             IO$M_READATTN   pseudodevice characteristics
                         IO$M_WRTEATTN   for subsequent operations.
    IO$_WRITEVBLK        IO$M_           Writes a virtual block.
    p1,p2,p3,p4,p5       INTERRUPT