X25(7)                     Linux Programmer's Manual                    X25(7)

       x25 - ITU-T X.25 / ISO-8208 protocol interface.

       #include <sys/socket.h>
       #include <linux/x25.h>

       x25_socket = socket(AF_X25, SOCK_SEQPACKET, 0);

       X25 sockets provide an interface to the X.25 packet layer protocol.
       This allows applications to communicate over a public X.25 data network
       as standardized by International Telecommunication Union's
       recommendation X.25 (X.25 DTE-DCE mode).  X25 sockets can also be used
       for communication without an intermediate X.25 network (X.25 DTE-DTE
       mode) as described in ISO-8208.

       Message boundaries are preserved — a read(2) from a socket will
       retrieve the same chunk of data as output with the corresponding
       write(2) to the peer socket.  When necessary, the kernel takes care of
       segmenting and reassembling long messages by means of the X.25 M-bit.
       There is no hard-coded upper limit for the message size.  However,
       reassembling of a long message might fail if there is a temporary lack
       of system resources or when other constraints (such as socket memory or
       buffer size limits) become effective.  If that occurs, the X.25
       connection will be reset.

   Socket addresses
       The AF_X25 socket address family uses the struct sockaddr_x25 for
       representing network addresses as defined in ITU-T recommendation

           struct sockaddr_x25 {
               sa_family_t sx25_family;    /* must be AF_X25 */
               x25_address sx25_addr;      /* X.121 Address */

       sx25_addr contains a char array x25_addr[] to be interpreted as a null-
       terminated string.  sx25_addr.x25_addr[] consists of up to 15 (not
       counting the terminating null byte) ASCII characters forming the X.121
       address.  Only the decimal digit characters from '0' to '9' are

   Socket options
       The following X.25-specific socket options can be set by using
       setsockopt(2) and read with getsockopt(2) with the level argument set
       to SOL_X25.

              Controls whether the X.25 Q-bit (Qualified Data Bit) is
              accessible by the user.  It expects an integer argument.  If set
              to 0 (default), the Q-bit is never set for outgoing packets and
              the Q-bit of incoming packets is ignored.  If set to 1, an
              additional first byte is prepended to each message read from or
              written to the socket.  For data read from the socket, a 0 first
              byte indicates that the Q-bits of the corresponding incoming
              data packets were not set.  A first byte with value 1 indicates
              that the Q-bit of the corresponding incoming data packets was
              set.  If the first byte of the data written to the socket is 1,
              the Q-bit of the corresponding outgoing data packets will be
              set.  If the first byte is 0, the Q-bit will not be set.

       The AF_X25 protocol family is a new feature of Linux 2.2.

       Plenty, as the X.25 PLP implementation is CONFIG_EXPERIMENTAL.

       This man page is incomplete.

       There is no dedicated application programmer's header file yet; you
       need to include the kernel header file <linux/x25.h>.
       CONFIG_EXPERIMENTAL might also imply that future versions of the
       interface are not binary compatible.

       X.25 N-Reset events are not propagated to the user process yet.  Thus,
       if a reset occurred, data might be lost without notice.

       socket(2), socket(7)

       Jonathan Simon Naylor: “The Re-Analysis and Re-Implementation of X.25.”
       The URL is ⟨ftp://ftp.pspt.fi/pub/ham/linux/ax25/x25doc.tgz⟩.

       This page is part of release 5.06 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2017-09-15                            X25(7)