HP X.25/9000 Programmer's Guide

124 AppendixA
X.25 Packet Formats
INTERRUPT Packet
INTERRUPT Packet
A application process sends an INTERRUPT packet to transmit
out-of-band data to the remote process.
Figure A-5 INTERRUPT packet
Access to the fields in the INTERRUPT packet is described below:
General Format
Identifier
Indicates the packet sequence count (modulo 8 or modulo 128). This field
cannot be read or written by an X.25 application.
Logical Channel
Identifier
Associates a logical channel number with the VC. This field is controlled
by the subsystem. It can be read with ioctl(X25_RD_LCI).
Packet Type
Identifier
Indicates the kind of packet. This field cannot be read or written directly,
but through system calls INTERRUPT packets can be transmitted or
detected.
To read this field on an incoming packet:
recv(MSG_OOB) returns a buffer the second byte of which ( buf[1] )
contains an indication that an INTERRUPT packet has arrived
(OOB_INTERRUPT).
To write this field on an outgoing packet:
Use the send(MSG_OOB) system call to transmit an INTERRUPT packet.
Interrupt User
Data
Contains data associated with the INTERRUPT packet.
To read this field on an incoming packet:
Logical Channel Identifier
87654321
1
2
3
Bits
Packet Type Identifier
General Format Identifier
Octets
Interrupt User Data
36960-90061.bk Page 124 Friday, November 10, 2000 3:42 PM