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

       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 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  re-
       trieve the same chunk of	data as	output with the	corresponding write(2)
       to the peer socket.  When necessary, the	kernel takes care of  segment-
       ing  and	 reassembling long messages by means of	the X.25 M-bit.	 There
       is no hard-coded	upper limit for	the message size.   However,  reassem-
       bling 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  buf-
       fer 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  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 null byte) ASCII characters forming the X.121
       address.	 Only the decimal digit	characters from	'0'  to	 '9'  are  al-

   Socket options
       The following X.25-specific socket options can be set by	using setsock-
       opt(2) and read with getsockopt(2)  with	 the  level  argument  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	 addi-
	      tional  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_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 <>.

       This  page  is  part of release 3.74 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

Linux				  2012-08-05				X25(7)


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