6100 ADCCP Programming Manual

Making an X.21 Leased-Line Connection
Writing Applications that Use ADCCP/X21
5–4 069225 Tandem Computers Incorporated
Your application should separate distinct facility request signals within the block
with a comma (,) and use a hyphen (-) at the end of the entire block to separate it
from the address signal that follows. If your application includes a facility request
block, it is inserted at the beginning of the selection signal sequence, before the
address signal.
The following example is a 13-byte selection-signal sequence consisting of two facility
request signals followed by a full address signal:
61,62-120302+
The first facility request signal is “61.” This is a request for charging information. The
second facility request signal, “62,” is a request for called line identification. The
address signal is “120302.” The facility request block is separated from the address
signal by a hyphen (-), and the entire selection signal sequence is terminated by a plus
(+).
For a more formal description of the selection signal sequence, refer to Annex D of the
CCITT X.21 Recommendation.
Anticipating the Netinfo
Sequence
If you want ADCCP/X21 to deliver DCE-provided information (such as call progress
signals or the called line address) to your application during connection establishment,
the (84) CONNECT request must include a value in the Text In field that is large
enough to accommodate the anticipated string. If you specify a value for Text In that
is too small, ADCCP/X21 will truncate the Netinfo sequence to fit the buffer you have
provided.
The (84)CONNECT request is described in detail in Section 6, “Requests and
Responses.”
Making an X.21
Leased-Line
Connection
The procedures for establishing and releasing X.21 connections on leased lines are
easier to implement than the procedures for circuit-switched lines. On a leased line,
you never need to issue an (82) CONNECT request after the line has been started
because the completion of a (6) START OPERATION request indicates that a
connection is already established. Thus, as soon as your application receives an error-
free (6) START OPERATION response, ADCCP stations can be set up and frame
transfer can begin. Similarly, to release a connection on a leased line, your application
can use the (7)STOP OPERATION request.
An application written for a circuit- switched line can be transferred to a leased line
with minimal changes. If you want to transfer such an application, you need to be
aware of the following considerations:
The value of the CIRCUIT-SWITCHED parameter in any (80) SET X.21
CONFIGURATION request must be 0 for leased service. This is the default value
for this parameter.
ADCCP/X21 is in the connected state after a (6)START OPERATION request
finishes successfully. If your application then issues a (82)CONNECT request,
ADCCP/X21 immediately returns an (82)CONNECT response with status 0,
indicating successful completion.