интерфейс протокола ITU-T X.25 / ISO-8208 (ITU-T X.25 / ISO-8208 protocol interface)
Имя (Name)
x25 - ITU-T X.25 / ISO-8208 protocol interface
Синопсис (Synopsis)
#include <sys/socket.h>
#include <linux/x25.h>
x25_socket = socket(AF_X25, SOCK_SEQPACKET, 0);
Описание (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 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
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
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.
Версии (Versions)
The AF_X25 protocol family is a new feature of Linux 2.2.
Ошибки (баги) (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.
Смотри также (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⟩.
