X25(7)                     Linux Programmer's Manual                    X25(7)
       x25, PF_X25 - ITU-T X.25 / ISO-8208 protocol interface.

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

       x25_socket = socket(PF_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  standardised 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 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 connec-
       tion will be reset.

       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 0) ASCII characters forming the X.121 address.
       Only the decimal digit characters from '0' to '9' are allowed.

       The following X.25 specific socket options can be set by using setsock-
       opt(2)  and  read  with  getsockopt(2)  with the level parameter 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 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 indi-
              cates 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.

       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

       The PF_X25 protocol family is a new feature of Linux 2.2.

Linux Man Page                    1998-12-01                            X25(7)