HP X.25/9000 Programmer's Guide

78 Chapter5

Receiving and Transmitting Out-of-band Information

Transmitting Out-of-band Events

There are three types of out-of-band events that can be sent by the X.25

application: CLEAR packets, RESET packets, and INTERRUPT packets.

These packets can be sent at any time as the program requires. While

Chapter 3 discussed the use of the close() system call for the

transmission of CLEAR packets, this chapter describes the use of the

cause and diagnostic codes, as well as the facilities and user data ﬁelds.

Clearing a Switched Virtual Circuit

An SVC can be cleared when one of the processes that use it (X.25 or the

network provider) issues a CLEAR REQUEST packet. A CLEAR

REQUEST packet can be sent by the X.25 application (with a close()

call), or it is be sent if the process terminates without executing a

close() call.

Once a CLEAR REQUEST packet is issued, data cannot be sent or

received over the connection because the connection is destroyed. The

X.25 application can control the contents of certain data ﬁelds in the

CLEAR REQUEST packet. These ﬁelds and the ioctl() calls which

control them are:

• cause code – ioctl(X25_WR_CAUSE_DIAG)

• diagnostic code – ioctl(X25_WR_CAUSE_DIAG)

• facilities – ioctl(X25_WR_FACILITIES)

• user data – ioctl(X25_WR_USER_DATA)

All of these calls must be issued prior to the close() call. The

ioctl(X25_WR_CAUSE_DIAG) and ioctl(X25_WR_USER_DATA) calls are

described below. The ioctl(X25_WR_FACILITIES) call is described in

Chapter 6 , “Extended Features.”

The ioctl(X25_WR_CAUSE_DIAG) Call

The cause code that is sent depends on the cause code speciﬁed with the

ioctl(X25_WR_CAUSE_DIAG call and the network type speciﬁed during

X.25 interface conﬁguration. The table below summarizes cause code

36960-90061.bk Page 78 Friday, November 10, 2000 3:42 PM