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x25(7)
X25(7) Linux Programmer's Manual X25(7)
NAME
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 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
buffer size limits) become effective. If that occurs, the X.25 connec‐
tion 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‐
lowed.
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
SOL_X25.
X25_QBITINCL
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.
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_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.
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 5.02 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
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 X25(7)