SNAX/APN Application Programming Manual

The SNALU Interface
SNAX/APN Application Programming Manual—420111-001
4-11
Initiating LU-LU Sessions
The PLU can send an unsolicited BIND request to the SLU, or the SLU can solicit a
BIND request by an SNA INIT-SELF request or a character-coded logon request
(the PLU still, however, formats and sends the BIND request).
This is described in detail under Initiating LU-LU Sessions
on page 4-11.
2. Data Exchange
Once an LU-LU session is established, the application on the Tandem system
communicates with the remote LU by way of WRITEREAD procedure calls. The
application uses the SNAX header in the application I/O buffer referenced by the
WRITEREAD call to control such functions as normal-flow and expedited-flow
transmission, sequence number maintenance, chaining, bracketing, pacing, and
request/response modes.
This is described in detail under Exchanging Data
on page 4-17.
3. Session Termination
There are several ways to terminate LU-LU sessions:
•
The PLU can send an unsolicited UNBIND request to the SLU. Some device
LUs also require the use of a CLEAR request before the UNBIND request.
•
The SLU can send an unsolicited UNBIND request to the PLU.
•
The SLU can send a TERM-SELF request or a character-coded logoff message
to the PLU, causing the PLU to send an UNBIND request.
•
In response to an operator command or upon detecting an irrecoverable error
condition, SNAX/APN generates two UNBIND requests (one sent to the PLU,
one sent to the SLU).
This is described in detail under Terminating LU-LU Sessions
on page 4-21.
Initiating LU-LU Sessions
The following subsections describe ways in which SNAX/APN SNALU applications
enter into LU-LU sessions with an SNA device connected to, or applications resident on,
a remote node type 2.1.
Starting the LUs
The LUs must be started. Tandem-controlled LUs are started using the SCF START
command.
Opening an LU
SNALU applications obtain access to remote LUs by issuing calls to the file-system
OPEN procedure. The general form of an OPEN call is:
CALL OPEN (filename, filenum, flags)