HP X.25/9000 Programmer's Guide

Appendix A 113

X.25 Packet Formats

CALL REQUEST/INDICATION Packet

A client process sends a CALL REQUEST packet to establish a VC with

a remote host. The packet is transmitted when a connect() system call

is issued. When the X.25 subsystem receives a CALL INDICATION

packet and locates a socket whose bind address matches the speciﬁed

called address, it allows the associated listen socket to unblock an

accept() system call or select “readable.”

Figure A-1 CALL REQUEST packet

Access to the ﬁelds in the CALL REQUEST/INDICATION packet is

described below:

General Format

Identiﬁer

Indicates D bit and packet sequence count. This ﬁeld cannot be read by

an X.25 application. The D bit cannot be read or written by an X.25/800

application. The packet sequence count (X.25 supports modulo 8 and

modulo 128) is set at conﬁguration time and cannot be read or written by

the application. However, the application can read the conﬁguration ﬁle

where this information can be posted.

To read this ﬁeld on an incoming packet:

Logical Channel Identifier

Called DTE Address Length

DTE Addresses

Facilities

87654321

Bits

Called DTE Address Length

Facility Length

Packet Type Identifier

General Format Identifier

Octets

Call User Data

36960-90061.bk Page 113 Friday, November 10, 2000 3:42 PM