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.
The
AF_X25 socket address family uses the
struct sockaddr_x25 for
representing 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.
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.
- X25_QBITINCL
- 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