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 recommenda-
       tion X.25 (X.25 DTE-DCE mode).  X25 sockets can also be used for commu-
       nication  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 connec-
       tion will be reset.

   Socket addresses
       The AF_X25 socket address family uses the struct sockaddr_x25 for  rep-
       resenting network addresses as defined in ITU-T recommendation X.121.

           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 setsock-
       opt(2) and read with getsockopt(2)  with  the  level  argument  set  to

              Controls whether the X.25 Q-bit (Qualified Data Bit) is accessi-
              ble 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  addi-
              tional  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_EXPERI-
       MENTAL 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 4.15 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)
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