6100 ADCCP Programming Manual

5 Writing Applications that Use
ADCCP/X21
069225 Tandem Computers Incorporated 5–1
This section describes the application tasks and the factors you should consider when
writing applications that communicate with stations on X.21 lines.
Application Tasks For an application to communicate over an ADCCP line, the application must perform
a specific set of tasks concerned with establishing and clearing an X.21 connection.
These tasks are:
Opening the line
Setting line parameters
Preparing to receive asynchronous messages
Starting the X.21 link
Requesting or canceling optional X.21 network facilities
Making an X.21 connection (circuit -switched or leased-line)
Preparing for unexpected disconnects of the data communications equipment
(DCE)
Performing ADCCP tasks:
Define a station list
Establish ADCCP protocol relationships
Transfer data
Shut down the ADCCP link
Clearing the X.21 connection
Closing the line
Recovering from errors
Once an X.21 connection is set up, your application can transfer and receive data with
the remote station using an ADCCP protocol. See Section 4, “Writing Applications
That Use ADCCP,” for a description of the application tasks related to setting up an
ADCCP link, establishing stations, and transferring packets. These tasks are the same
for ADCCP/X21 as they are for 6100 ADCCP.
Opening the Line Any application that wants to use the line must first open it. Just as with 6100
ADCCP, you open an ADCCP/X21 line with a call to the Guardian 90 OPEN
procedure. The parameters that you specify in the OPEN call have the same
significance for ADCCP/X21 as they do for 6100 ADCCP lines. See “Opening the
Line” in Section 4 for a description of how to open a line.