Pathway/iTS TCP and Terminal Programming Guide

Designing Your Application
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
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IDS Requesters
3. After constructing an appropriate response, requesters reply to an unsolicited
message by performing a REPLY TO UNSOLICITED MESSAGE statement.
IDS Requesters
Standard SCREEN COBOL requesters are screen oriented; they send data back and
forth between the Working-Storage Section of the program and a terminal’s display
screen by using screen templates defined in the Screen Section. Standard SCREEN
COBOL requesters use SCREEN COBOL ACCEPT and DISPLAY statements in the
Procedure Division to interact with display terminals.
SCREEN COBOL requesters that employ the intelligent device support (IDS) facility
within the TCP send data back and forth between the Working-Storage Section and an
intelligent device (or a front-end process that controls the device) by using message
templates defined in the Message Section in the Data Division. IDS requesters use
SCREEN COBOL SEND MESSAGE statements and their associated REPLY clauses in
the Procedure Division to interact with the intelligent devices or front-end processes.
Although the IDS facility sends and receives data through Message Section templates
instead of Screen Section templates, the TCP still provides:
•
Link management for access to Pathway server classes
•
TMF support to ensure transaction protection and database integrity
•
Fault tolerance through process pairs
•
Multithreading and multitasking
•
Expanded I/O editing support for data streams from intelligent devices
Design Considerations
When using IDS to facilitate access to Pathway servers by intelligent devices, consider
the following:
•
IDS requester programs are written and compiled in the same way as standard
SCREEN COBOL requesters.
•
A controlling SCREEN COBOL program unit does not control the intelligent device
or front-end process or use any information about the characteristics of the device.
The programming within the device or process must start the device or process
itself, accept messages from the TCP, and determine if and when to reply to the
TCP.
•
The intelligent device supplies the presentation services (that is, screen displays)
suitable to its capabilities.
•
Terminal types not supported by the TCP can use a front-end process (such as a
GDSX process) in conjunction with IDS, as described under Requesters Using
GDSX later in this section.