Envoy ACP/XF Application Programming Manual

EnvoyACP/XF and the Application Task
EnvoyACP/XF Application Programming Manual–132179
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Application Tasks
Application Tasks
When communicating with stations over a bit-synchronous communications line, an
application process must perform certain line-handling tasks. The number of such tasks
and the means of performing them differ depending on whether:
•
The protocol chosen is ADCCP-ABM, HDLC, ADCCP-NRM, or SDLC
•
The line is switched or nonswitched
•
The local station is supervisory, tributary, or combined
The application process performs the following tasks:
•
Opening a line*
•
Setting line-configuration parameters (optional)
•
Establishing and controlling a data link*
•
Transferring data
•
Shutting down a data link*
•
Closing a line*
•
Recovering from errors
•
Automatic calling (using V.25 bis modems)
* Opening a line means creating an object in the line handler process that is associated with a data link and which
defines the characteristics of that data link. Establishing a link refers to the process of going across the
communication lines, bringing up the remote modem (Data Circuit Terminating Equipment or DCE). Shutting
down a link involves shutting down the remote terminal. Closing a line removes the LINE object from the line
handler process making the line inaccessible to the application.
General application information for performing these tasks is described in this section.
Protocol-specific considerations relating to these tasks are described in Sections 2
through 4.
Opening a Line
An application must open a communications line before it can send or receive
communications on that line. Your application performs this task by sending a call to the
file-system FILE_OPEN_ procedure.
A single FILE_OPEN_ call can support no more than 15 pending READ or WRITE
calls.