INTERRUPT CONFIRMATION Packet

This packet is transmitted automatically by the X.25/300 subsystem when an INTERRUPT packet is received. The X.25/800 subsystem transmits this packet when the application process reads the interrupt data (issues a recv(MSG_OOB) system call).

Figure A-6 INTERRUPT CONFIRMATION Packet

The access to the fields in the INTERRUPT CONFIRMATION 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

Contains the logical channel identifier. It is controlled by the subsystem. It can be read with the ioctl(X25_RD_LCI) after the call has been estab lished.

Packet Type Identifier

Indicates the kind of packet. X.25/300 automatically transmits this packet in response to an INTERRUPT packet, and transmission cannot be controlled by the application.

To read this field on an incoming packet:In blocking mode, the send(MSG_OOB) system call blocks until confirma tion is received. In nonblocking mode, recv(MSG_OOB) returns a buffer the second byte of which (buf[1]) indicates that an INTERRUPT CONFIRMATION packet has arrived (OOB_VC_INTERRUPT_CONF).

To write this field on an outgoing packet:The X.25/800 subsystem transmits an INTERRUPT CONFIRMATION packet when the corresponding INTERRUPT packet's interrupt user data field is read with a recv(MSG_OOB) system call.