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

       x25, AF_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 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 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 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.

              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 com-

       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

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2008-08-08                            X25(7)