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

NAME

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

SYNOPSIS

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

       x25_socket = socket(AF_X25, SOCK_SEQPACKET, 0);

DESCRIPTION

       X25  sockets  provide an interface to the X.25 packet layer protocol.  This allows applications to communicate over a public X.25 data net-
       work 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 sys-
       tem 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 representing 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
       allowed.

   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.

       X25_QBITINCL
	      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 correspond-
	      ing outgoing data packets will be set.  If the first byte is 0, the Q-bit will not be set.

VERSIONS

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

BUGS

       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.

SEE ALSO

       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>.

COLOPHON

       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 https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15								    X25(7)