X25AM Programming Manual

X25AM Programming Manual—527201-001
1-1
1 Introduction
This section describes the X25AM process. The other topics covered in this section
include:
About the X25AM Process
X25AM, an I/O process, controls a communication line to an X.25 packet-switched
network. Application programs communicate with remote devices through an X25AM
process, using Guardian file-system procedures. X25AM supports user-developed
applications and NonStop software, such as PATHWAY, that use file system
procedures to communicate with devices.
Terminals connected to the network by a packet assembler/disassembler (PAD), other
host computers, and processes running on other NonStop systems are all examples of
remote entities supported by X25AM. X3PAD, a program that interfaces to X25AM and
functions as a PAD, is included with X25AM. X3PAD connects terminals on a NonStop
system to an X.25 packet-switched network.
Subdevices
An X25AM system I/O process controls a line, which is a physical entity. A line is
configured with multiple circuits, each of which can be used for call activity. Associated
with each line (the device) are subdevices, which are logical entities. The subdevice
provides a way for your application to communicate over a circuit (which can be
switched or permanent). The X25AM process is called a subsystem. Both lines and
subdevices are X25AM subsystem objects.
Your application uses the Guardian file system to communicate with an X25AM
subsystem. Information is transferred by the file system between the file-system
buffers of your application and the X25AM process. The file-system buffers are
associated with subdevices, which are treated as files by your application.
Your application opens a subdevice file using the standard $device-
name.#subdevice-name file-system format. Your application always accesses this
file using standard file-system procedures. When your application accesses a
subdevice, the application actually communicates with the X25AM process that
controls the line associated with the subdevice.
Topic Page
Call Setup, Data Transfer, and Call Clearing
1-2
Assigning Incoming Calls 1-5
Call Setup and Call Clearing Packets 1-6
Subscription Parameters 1-13
Per Call Facilities 1-16
Other X25AM Connection Methods 1-19
The Modem Interface 1-20