X25AM Programming Manual

Introduction
X25AM Programming Manual—527201-001
1-2
Application Protocols
Table 1-1 lists the most important file-system procedures used in your application.
Application Protocols
The X25AM subsystem exchanges information with your application by using one of its
application protocols. You select one of these protocols by associating it with the
subdevice file. The X25AM application protocols are:
•
the Interactive Terminal Interface (ITI), the protocol for exchanging information with
terminals connected to the network with a PAD device
•
the Process To Process (PTP), the protocol for exchanging data with remote
devices.
Other X25AM Protocols
Other X25AM protocols are the Network Access Method (NAM) protocol and the
Qualified Logical-Link Control (QLLC) protocol.
•
The NAM protocol is used to link Expand nodes with X.25 circuits. This protocol
cannot be used directly with an application.
•
The QLLC protocol is a link-level protocol used as an X.25 interface for attaching
SNA devices to packet-switched data networks (SNAX).
Call Setup, Data Transfer, and Call Clearing
Call setup, data transfer, and call clearing are terms describing the events that occur
during a virtual call on a switched virtual circuit (SVC). Data transfer is the only event
that occurs on a permanent virtual circuit (PVC).
Figure 1-1 illustrates the file-system procedures and packet-level activity associated
with each phase.
Table 1-1. File-system Procedures Used in an X25AM Application
Procedure Use
OPEN Open a subdevice. Use the file number for all other file-system
procedures.
CONTROL 11 Wait to be called.
CONTROL 17 Make a call.
READ Process an incoming message.
WRITE Send a message (does not require a reply).
WRITEREAD Send a message (requires a reply).
CONTROL 12 Clear a call (for PTP) or issue an invitation to clear a call (for ITI).
CLOSE Close a file.
CANCEL Cancel an operation.