ddp(3N)                                                   ddp(3N)



     NAME
          ddp_open, ddp_close - AppleTalk Datagram  Delivery  Protocol
          (DDP) interface

     SYNOPSIS
          #include <at/appletalk.h>
          #include <at/ddp.h>
          cc [flags] files -lat [libraries]

          int ddp_open(socket)
          at_socket *socket;

          int ddp_close(fd)
          int fd;

     DESCRIPTION
          The DDP interface provides applications with access to the
          AppleTalk DDP operations.

          The ddp_open routine opens a static or dynamic DDP socket
          and returns an AppleTalk socket file descriptor that can be
          used to read and write DDP datagrams.  The parameters are

          socket  A pointer to the DDP socket number to open. If the
                  AppleTalk socket number is 0, or if socket is NULL,
                  a DDP socket is dynamically assigned.  If socket is
                  non-NULL, the socket number is returned in socket.

                  An error condition results if there are no more
                  dynamic DDP sockets available, if the maximum number
                  of open files has been exceeded at a process or sys-
                  tem level, or if the network is offline.

                  Only the superuser can open a static DDP socket.

          fd      The AppleTalk file descriptor of the DDP socket to
                  be closed by the ddp_close routine.

          Datagrams are always read and written with the long DDP
          header format, using standard A/UX read(2) and write(2) sys-
          tem calls.  The long header DDP datagram is defined by this
          structure in <at/ddp.h>:

          typedef struct {
                  u_short     unused : 2,
                              hopcount : 4,
                              length : 10;
                  u_short     checksum;
                  at_net      dst_net;
                  at_net      src_net;
                  at_node     dst_node;
                  at_node     src_node;



     April, 1990                                                     1

     ddp(3N)                                                   ddp(3N)



                  at_socket   dst_socket;
                  at_socket   src_socket;
                  u_char      type;
                  u_char      data[DDP_DATA_SIZE];
          } at_ddp_t;

          When a datagram is written, only the fields checksum,
          dst_net, dst_node, dst_socket, type, and data need to be
          set.  The rest of the fields may be left uninitialized, be-
          cause DDP sets them.

          The length field is the DDP packet length. The checksum
          field contains the DDP checksum.  When datagrams are sent, a
          checksum is computed only if this field is nonzero.

          Datagrams can be sent and received asynchronously using
          standard A/UX facilities:  select(2N) or O_NDELAY fcntl(2).

     ERRORS
          All routines return -1 on error with detailed error code in
          errno:

          [EACCES]            A nonsuperuser attempted to open a stat-
                              ic AppleTalk socket.

          [EADDRINUSE]        The static socket is in use, or all
                              dynamic sockets are in use.

          [EINVAL]            An attempt was made to open an invalid
                              AppleTalk socket number.

          [EMSGSIZE]          A datagram is too large or too small.

          [ENETDOWN]          The network interface is down.

          [ENOBUFS]           DDP is out of buffers.

          Routines also return any additional error codes returned by
          standard A/UX open(2), close(2), read(2), and write(2) sys-
          tem calls.

     FILES
          /dev/appletalk/ddp/*

     SEE ALSO
          close(2), fcntl(2), open(2), read(2), select(2N), write(2),
          atp(3N), ddp(3N), nbp(3N), pap(3N), rmtp(3N), fcntl(5), ter-
          mio(7), Inside AppleTalk; ``AppleTalk Programming Guide,''
          in A/UX Network Applications Programming.






     2                                                     April, 1990