x25 - phpMan

X25(4) Linux Programmer’s Manual X25(4)

NAME
x25, PF_X25 - ITU-T X.25 / ISO-8208 protocol interface.

SYNOPSIS
#include <sys/socket.h>
#include <linux/x25.h>

x25_socket = socket(PF_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 standardised 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 re-assembling long messages by
means of the X.25 M-bit. There is no hard-coded upper limit for the message size.
However, re-assembling 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 net-
work 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 0)
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 parameter 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 corre-
sponding incoming data packets was set. If the first byte of the data writ-
ten 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.

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.