NAME
x25 - ITU-T X.25 / ISO-8208 protocol interface. SYNOPSIS
#include
#include
x25socket = socket(AFX25, SOCKSEQPACKET, 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 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 connec‐ tion will be reset. Socket addresses The AFX25 socket address family uses the struct sockaddrx25 for rep‐
resenting network addresses as defined in ITU-T recommendation X.121. struct sockaddrx25 { safamilyt sx25family; /* must be AFX25 */ x25address sx25addr; /* X.121 Address */ };
sx25addr contains a char array x25addr[] to be interpreted as a null- terminated string. sx25addr.x25addr[] 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 SOLX25. X25QBITINCL
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 AFX25 protocol family is a new feature of Linux 2.2. BUGS Plenty, as the X.25 PLP implementation is CONFIGEXPERIMENTAL. This man page is incomplete. There is no dedicated application programmer's header file yet; you need to include the kernel header file
. CONFIGEXPERI‐ 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 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-08-05 X25(7)