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



NAME
       x25, AF_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  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 re-assembling long messages by
       means of the X.25 M-bit.  There is no hard-coded upper limit for the message  size.
       However, re-assembling 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 net-
       work 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 0)
       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  corre-
              sponding incoming data packets was set.  If the first byte of the data writ-
              ten 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.

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_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.

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 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-08-08                            X25(7)

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