- Hewlett-Packard Printer User Guide

Using the VPO Application Programming Interfaces
The VPO Interfaces
Chapter 4180
Structure of the Legacy Link Process
Figure 4-6 is a flowchart to illustrate the order in which the API
functions are used when a legacy system is fully integrated.
The legacy link process in this description is a process that runs on the
management server. This process communicates with the VPO
management server processes using three instances of the interface:
❏ One to send (write) messages to the management server,
❏ One to receive (read) action requests from the management server,
❏ One to send (write) action responses to the management server.
In addition, the legacy link process must establish a bidirectional
communication channel with the legacy system to receive input for
generating messages and action responses, and to pass on action
requests received from the management server.
As soon as the communication channel between the legacy system and
the VPO management server is established, the legacy link process waits
for incoming data from both communication partners.
When incoming data originates from the legacy system, either an action
response or a message is generated and sent to the VPO management
server. If the incoming data originates from the VPO management
server, it is an action request that is processed, then sent to the legacy
system.
Note that action responses confirm that an action has occurred, for
example, an action response might show that an action has been
completed successfully. When immediate local actions are configured, an
action response should be sent to show that an action has completed even
though an action request was not received from the VPO management
server.