HP X.25/9000 Programmer's Guide

114 AppendixA
X.25 Packet Formats
CALL REQUEST/INDICATION Packet
This field cannot be read by the application.
To write this field on an outgoing packet:
X.25 700/800 applications use the ioctl(X25_SEND_TYPE)call to set the
D bit.
Logical Channel
Identifier
Associates a logical channel number with the VC. This field is controlled
by the X.25 subsystem. It can be read with ioctl(X25_RD_LCI) after the
call has been established.
Packet Type
Identifier
Indicates the kind of packet. This field cannot be read or written directly,
but through system calls, CALL REQUEST packets can be transmitted
or detected.
To read this field on an incoming packet:
Use the listen() and accept() system calls to detect the arrival of a
CALL REQUEST packet.
To write this field on an outgoing packet:
Use the connect() system call to transmit a CALL REQUEST packet.
Calling DTE
Address (Length)
Indicates the source of the packet.
To read this field on an incoming packet:
Use the accept() system call to return an x25addrstr structure
containing the calling DTE address of the incoming CALL REQUEST
packet.
To write this field on an outgoing packet:
The subsystem computes this field. If the local machine has multiple
X.25 interfaces connected to it, the client can select which interface (each
with a unique X.121 address) to use by specifying the x25ifname field in
the x25addrstr structure. The address is the X.121 configuration packet
address, plus the subaddress specified with an
ioctl(X25_WR_CALLING_SUBADDR) call.
Called DTE
Address (Length)
Indicates the destination of the packet. This field is accessed through the
x25addrstr structure.
To read this field on an incoming packet:
After the connection has been established, this field can be read using
the getsockname() system call.
36960-90061.bk Page 114 Friday, November 10, 2000 3:42 PM