x25(7) - Man pages

x25(7) Miscellaneous Information Manual x25(7)

NAME
x25 - ITU-T X.25 / ISO/IEC 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 de-
scribed in ISO/IEC 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 repre-
senting 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 allowed.

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 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.

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_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.