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  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
   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

       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
   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 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 4.09 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


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